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The Neck Pain Driving Index (NPDI) for chronic whiplash-associated disorders: development, reliability, and validity assessment
The Spine Journal 12 (2012) 912–920
Clinical Study
The Neck Pain Driving Index (NPDI) for chronic whiplash-associated disorders: development, reliability, and validity assessment Hiroshi Takasaki, MS*, Venerina Johnston, PhD, Julia M. Treleaven, PhD, Gwendolen A. Jull, PhD NHMRC Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, Division of Physiotherapy, School of Health and Rehabilitation Science, The University of Queensland, Brisbane, Queensland 4072, Australia Received 29 July 2011; revised 13 March 2012; accepted 25 September 2012
Abstract
BACKGROUND CONTEXT: Driving is a functional complaint of many individuals with chronic whiplash-associated disorders (WAD). Current driving scales do not include the most troublesome driving tasks for this group, which suggests that a new tool is required to assess perceived driving difficulty in this population. PURPOSE: To develop a Neck Pain Driving Index (NPDI) to assess the degree of perceived driving difficulty for individuals with chronic WAD and evaluate the reliability and validity of the NPDI. STUDY DESIGN: Descriptive/survey. PATIENT SAMPLE: An external panel of 15 researchers/clinicians and 87 participants with chronic WAD. OUTCOME MEASURES: The NPDI and a 0 to 10 numeric rating scale (NRS) of perceived driving difficulty (0, no difficulty and 10, maximum difficulty). METHODS: Phase 1 included the construction of a preliminary NPDI and content validity assessment of question items by a 15-member external panel. Comprehension was evaluated by seven participants with chronic WAD. In Phase 2, the final version of the NPDI was developed via descriptive analysis and assessment of internal consistency using responses of 87 participants with chronic WAD. Subsequently, the convergent validity was assessed using NRS scores. Test-retest reliability at 1 month was investigated in 25 of the 87 participants. Psychometric properties of the driving tasks in the final NPDI were categorized by the external panel, based on the hierarchal Michon model of driving task performance levels. An additional symptom section was developed to better understand the reasons for driving difficulties. RESULTS: The final NPDI included 12 driving tasks, which scored at least 80% on the content validity index (CVI), ensuring content validity. The NPDI demonstrated good internal consistency (a50.80), convergent validity (r50.51; p!.01), and test-retest reliability (intraclass correlation coefficient, 0.73; p!.01). As a result of the assessment of psychometric properties, driving tasks were categorized into the strategic (n53), tactical (n57), and operational (n52) levels in the Michon model. The content validity of 11 symptoms (CVI $80%) was established by the external panel. CONCLUSIONS: The NPDI was developed to assess the degree of perceived driving difficulty in the chronic whiplash population. Reliability and validity of the NPDI were ensured. The NPDI can be the entry point for discussions on driving difficulties between clinicians and patients with chronic WAD. Ó 2012 Elsevier Inc. All rights reserved.
Keywords:
Automobile driving; Neck pain; Questionnaire; Reliability and validity; Whiplash injuries
FDA device/drug status: Not applicable. Author disclosures: HT: Nothing to disclose. VJ: Nothing to disclose. JMT: Nothing to disclose. GAJ: Nothing to disclose. * Corresponding author. NHMRC Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, Division of Physiotherapy, School 1529-9430/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.spinee.2012.09.053
of Health and Rehabilitation Science, The University of Queensland, Brisbane, Queensland 4072, Australia. Tel.: (61) 7-3365-2275; fax: (61) 7-3365-1622. E-mail address: [email protected] (H. Takasaki)
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Introduction Driving is a functional task with which many people with chronic whiplash-associated disorders (WAD) report various difficulties [1–3], including a perceived reduction in their driving ability [3]. Thus, it is important to evaluate perceived driving difficulty in the chronic whiplash population to serve as a platform to understand the driving performance and safety in this group. Questionnaires have been developed to assess driving difficulty in specific populations, including those with visual impairments, stroke, advanced age, and/or dizziness [1,4– 7]. Recently, Takasaki et al. [3] found that the most troublesome driving tasks reported by individuals with chronic WAD were checking blind spots, prolonged driving, and reversing/reverse parking. However, these three driving tasks are not included in the current questionnaires. This indicates a need to develop a specific questionnaire to assess the degree of perceived driving difficulty in the chronic whiplash population and indeed those with neck pain disorders. When developing a new questionnaire, consideration should be given to the specific driving tasks causing difficulties and reasons why these are difficult. Additional information on symptoms that may adversely affect driving would offer the clinician an opportunity to open discussion on driving in the chronic whiplash population. Furthermore, the specific driving tasks that may be difficult should be considered in relation to a hierarchal model of driving tasks such as the Michon model [8,9]. This model’s hierarchy is the strategic, tactical, and operational levels. The strategic level refers to the planning of general driving such as driving time and route [8,9]. The tactical level relates to the observation/selection of signals and planning of actions depending on traffic conditions. The operational level refers to specific and automatic actions such as turning the steering wheel and changing gears. Normal driving is generally performed with a topdown influence [9,10]. For example, to drive in an environment with constantly changing traffic conditions such as city driving (strategic level) requires significant mental effort. This limits available resources for tasks such as checking mirrors (tactical level). Insufficient observation skills increase chances of unexpected situations that may require sudden braking and quick steering control (operational level). Thus, a questionnaire that can assess driving difficulty over these three levels would be useful. However, to date, there has been no questionnaire structured in this way. The purpose of this study was twofold. The primary aim was to develop a questionnaire—the Neck Pain Driving Index (NPDI)—to assess the degree of perceived driving difficulty in the chronic whiplash population. The second aim was to establish the reliability and validity of the NPDI.
Methods The NPDI was developed via a two-phase process, which included the development of a preliminary version
Context Assessment of functional limitations allows treating physicians to better understand a patient’s current status and response to treatment. In this article, the authors present a questionnaire affording such assessment regarding driving and whiplash-associated disorders (WAD). Contribution The authors provide an early attempt to establish a reliable and valid method of assessing self-perceived driving impairment. Their analysis found good test-retest reliability and apparent validity of self-reported perceived impairment in a small number of test subjects, including subjects in litigation. Implication Although testing this index against external validation remains to be performed, validated measures are vital for the assessment of outcomes. Disease/functionspecific measures, such as this one, if further developed and independently validated, may allow treating physicians to identify prognostic subgroups or interventions that might specifically address an important aspect of a patient’s problem. —The Editors
followed by the development of a final version (Figure). This study was approved by the institutional human medical ethics committee. All participants provided informed consent. Phase 1: Development of a preliminary NPDI Question items (driving tasks and symptoms) for the NPDI were generated, and the content validity of each question item was assessed by an external panel before administering a preliminary draft of the NPDI to a sample of individuals with chronic WAD for readability and comprehension. Participants For the external panel, 18 people were approached, on the basis of their research and publication record and/or clinical experience in the field of WAD, to participate in a study to establish the content validity of the preliminary draft of the NPDI. Fifteen people agreed to join an external panel and comprised 11 researchers and four clinicians. The external panel came from the following disciplines: medical doctor (1), physiotherapy (13), and chiropractic (1). The external panel had a mean (standard deviation) research/ clinical experience with whiplash of 23.3 (8.9) years.
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disorders). Seven chronic WAD patients participated in Phase 1. Their characteristics are presented in Table 1.
Figure. The development of a two-phase NPDI. 1Assessed using data from external panel. 2Assessed using data from patients with chronic WAD who were recruited from a whiplash clinic in a local university. 3Assessed using data from the chronic whiplash population in Australia. 4Included the flooring and ceiling effects. NPDI, Neck Pain Driving Index; WAD, whiplash-associated disorders.
Chronic WAD patients were recruited from a university whiplash clinic to provide feedback on English expression and comprehension of the preliminary draft of the NPDI. Inclusion criteria were currently driving and aged between 20 and 60 years and neck pain for at least 3 months to 5 years after whiplash injury. Patients were excluded if they had a cervical fracture or dislocation, potential head injury including loss of consciousness at the time of the whiplash injury, upper or lower limb fractures/injuries, or any comorbid medical problems that could affect driving performance (eg, neurologic, cardiovascular, respiratory, and visual
Procedure Phase 1 was completed in three steps. First, possible driving tasks and symptoms, which may be important for the assessment of perceived driving difficulty, were generated from a review of the literature and discussions between the authors. A first draft of a preliminary NPDI was then developed, which included 27 driving tasks and eight symptoms (Tables 2 and 3). Second, the content validity of each driving task and symptom was examined by the external panel. The use of both the content validity index (CVI) and multirater kappa coefficient of agreement provides more rigorous assessment of the content validity than the use of the CVI alone [11], but the use of both may be too restrictive for the developmental stage of a new questionnaire. Thus, this study used the CVI to assess the content validity in the first phase. The external panel rated the relevance of the driving tasks and symptoms to driving difficulty for individuals with chronic WAD using a four-point scale: not relevant, somewhat relevant, quite relevant, and very relevant in Draft 1 of the preliminary NPDI. The CVI, which is the proportion of driving tasks and symptoms receiving a rating of ‘‘quite relevant’’ or ‘‘very relevant,’’ was calculated. Driving tasks and symptoms with less than 80% in the CVI were rejected from the item list because of the unacceptable level of agreement [12–14]. As a result, 12 driving tasks were rejected from the item list (Tables 2 and 3). The external panel was also requested to nominate additional driving tasks and symptoms not included in Draft 1 that might be related to driving difficulty for individuals with chronic WAD. In response, a second draft of the preliminary NPDI was constructed. It included an additional six driving tasks and nine symptoms and was sent to the same external panel for reassessment of the CVI. The review of the CVI of the second draft resulted in the exclusion of one driving task and six symptoms (Tables 2 and 3). Consequently, a third draft of the preliminary NPDI was written, comprising 20 driving tasks and 12 symptoms (Tables 2 and 3). In the third step, seven chronic WAD patients reviewed Draft 3 of the preliminary NPDI and provided feedback on wording and English expression for the driving tasks
Table 1 Characteristics of the participants with chronic whiplash-associated disorders in Phases 1 and 2 Phase 2 Variables
Phase 1 (n57)
Total sample (N587)
Reliability study sample (n525)
Age, mean (SD), y Driving experience, mean (SD), y Total kilometers driven per week, mean (SD), km Time since accident, mean (SD), mo NDI, mean (SD) Female, n (%)
31.9 13.9 148.6 13.7 55.4 6
38.4 19.5 252.9 21.5 37.5 69
41.6 22.7 286.4 20.7 38.2 21
SD, standard deviation; NDI, The Neck Disability Index.
(7.3) (7.3) (132.6) (11.0) (8.0) (86)
(11.5) (11.5) (278.6) (16.7) (16.4) (80)
(12.7) (12.8) (283.1) (16.7) (18.9) (84)
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Table 2 Content validity of driving tasks as assessed by the 15-member external panel
Driving tasks Accelerating suddenly Anticipating potential risks (eg, pedestrians and cyclists)* Braking suddenly* Changing lanes* Checking blind spots* Driving alone Driving an unfamiliar car (eg, a rental car and spouse’s car) Driving in bad weather conditions (eg, rain)* Driving in unfamiliar areas Driving for less than 30 min* Driving for more than 1 h* Driving near (your) accident site* Driving on a bumpy road* Driving on a freeway Holding conversations while driving Judging distance in the rear view mirror Judging the distance in front* Merging on expressways* Navigating roundabouts Night driving* Operating CDs/radio while driving Peak/rush hour driving Reading traffic signs while driving* Reversing* Turning at intersections without traffic lights Turning right oncoming traffic Turning the steering wheel quickly* Changing gears* Controlling the steering wheel with both hands* Driving at dusk* Driving in variable light (eg, in and out of a tunnel) Driving with passengers* Visually tracking moving objects (eg, other cars)*
Initially listed U U U U U U U U U U U U U U U U U U U U U U U U U U U
Accepted by the first content validity assessment
Added after the first content validity assessment
Accepted by the second content validity assessment
U U U U U U U U U
U U U U U U
U U U U U U
U U U U U
CVI (%) 73 93 93 93 93 73 60 100 73 80 93 93 87 73 40 73 87 87 73 87 60 73 87 100 73 73 93 80 80 80 73 80 100
Retained after pilot trial U U U U U U U U U
U U U U U U U U U U U
CVI, content validity index; CD, compact disc. * Driving tasks retained for the final draft of the preliminary Neck Pain Driving Index.
and symptoms, which resulted in vertigo and dizziness being combined. The final version of the preliminary NPDI included 20 driving tasks and 11 symptoms (Tables 2 and 3). Phase 2: Development of a final version of the NPDI The driving task section of the preliminary NPDI was the focus of the Phase 2 research. Procedures included the development of a final version of the NPDI via the assessment of flooring and ceiling effects and internal consistency of the 20 driving tasks of the preliminary NPDI and examination of the construct validity in particular the convergent validity, test-retest reliability, and psychometric properties of the driving tasks retained in the final version of the NPDI. The symptom section was additional and designed to assist the understanding of possible reasons for the driving difficulty. Data on symptoms retained (CVI $80% in Phase 1) were collected for descriptive purposes.
Participants Participants with chronic WAD were recruited through advertising in the popular press and in community practices in Australia from June 2010 to June 2011 to develop the final version of the NPDI. Participant inclusion and exclusion criteria were identical to Phase 1. Eighty-seven people with chronic WAD participated in Phase 2. In addition, 25 of the 87 participants agreed to participate in the assessment of test-retest reliability of the NPDI after a 1-month interval. The characteristics of primary and subset groups are presented in Table 1. The same external panel recruited in Phase 1 assessed the psychometric property of each driving task of the final version of the NPDI for their placement within the Michon model. Procedure A package of questionnaires was forwarded electronically or in hardcopy to the 87 participants with chronic WAD to examine the flooring and ceiling effects, internal consistency,
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Table 3 Content validity of symptoms as assessed by the 15-member external panel
Symptoms Arm pain* Difficulty concentrating* Fatigue* Headache* Limited neck movement* Neck pain* Stress/anxiety* Unable to move your head quickly* Dizziness* Depression Fearfulness* Irritable mood Limited trunk movement Muscle weakness Nausea* Tinnitus Vertigo
Initially listed
Accepted by the first content validity assessment
U U U U U U U U
U U U U U U U U
Added after the first content validity assessment
U U U U U U U U U
Accepted by the second content validity assessment
U
U U
CVI (%) 100 87 87 93 100 100 100 100 93 27 93 47 73 33 93 33 93
Retained after pilot trial U U U U U U U U U U
U
CVI, content validity index. * Symptoms retained for the final Neck Pain Driving Index.
convergent validity, and test-retest reliability of NPDI. The completed questionnaires were returned electronically or in a self-enclosed envelope. The questionnaires could be completed within 15 minutes. The package included the preliminary NPDI (driving task and symptom sections), a 0 to 10 numeric rating scale (NRS) of perceived driving difficulty, and the Neck Disability Index (NDI). One month later, the 25 participants completed the preliminary NPDI (driving task section) again to obtain data for the assessment of testretest reliability of the final version of the NPDI. The preliminary NPDI The construct of the preliminary NPDI requested respondents to rate the degree of difficulty in performing each driving task during the last 3 months on a four-point Likert scale: no difficulty (Score 0), slight difficulty (Score 1), moderate difficulty (Score 2), and great difficulty (Score 3). If the respondent had not undertaken a certain driving task, the options were either because of reasons not related to my injury (not applicable [NA]) or because of my injury (Score 4). Not applicable responses were excluded for item scoring. The respondents’ scores in each task were summed and expressed as a percentage of the total possible score. A score of 0% indicated no difficulty, whereas 100% indicated maximum perceived difficulty. The total score (percentage) was calculated for the items retained in the final version of the NPDI to examine the convergent validity and test-retest reliability. In the symptom section, respondents were asked to rate how much each symptom had adversely affected their driving ability during the last 3 months on a five-point scale: NA (if a symptom has not been experienced), does not affect driving at all, adversely affects driving slightly, adversely affects driving moderately, or adversely affects driving greatly.
Numeric Rating Scale of perceived driving difficulty Participants rated their perceived driving difficulty with a single question, ‘‘Overall have you had any difficulty driving following your injury?’’ on an NRS (0, no difficulty and 10, maximum difficulty). This scale was used to investigate the convergent validity of the final version of the NPDI. Neck Disability Index The NDI is a 10-item questionnaire assessing global disability due to neck pain, and although it includes one question regarding driving, it was not designed to specifically assess disability for driving [15]. Each item has six different assertions corresponding to scores of 0 to 5. The total score is expressed in percentiles with 100% being the highest level of disability associated with neck pain. The NDI has good concurrent validity [2,16,17] and internal consistency (a50.87) in the whiplash population [17]. Hence, this scale was used to investigate correlation to the final version of the NPDI and understand the characteristics of the participants in this study. Statistical procedures Responses from the 87 participants with chronic WAD in the driving task section of the preliminary NPDI were initially analyzed descriptively. Driving tasks were excluded from the item list when more than 40% of responses were NA. All remaining responses were examined for flooring and ceiling effects. A flooring or ceiling effect was considered when more than 50% of the responses (excluding NA scores) were the minimum (Score 0) or maximum (Score 4) response [18]. Driving tasks with flooring or ceiling effects were excluded.
H. Takasaki et al. / The Spine Journal 12 (2012) 912–920
The internal consistency for driving tasks retained was computed with Cronbach a. Driving tasks were excluded from the item list when the hypothetical value of a was higher than the total value of a. From this analysis, the NPDI (ie, final version) was developed (see Supplementary Appendix). Data from the 87 participants for the NPDI and NRS were not normally distributed (Kolmogorov-Smirnov tests). Hence, the convergent validity was evaluated by calculating Spearman r between the score of the NPDI at the first administration of the preliminary NPDI and NRS of perceived driving difficulty. Spearman r was also used to examine the correlation between the scores of the NDI and first administration of the preliminary NPDI. The data of 25 participants from the driving tasks retained in the first and second administrations of the preliminary NPDI were normally distributed (Shapiro-Wilk tests). The test-retest reliability of the NPDI (1-month interval) was determined with the intraclass correlation coefficient. Demographic data were compared between the total sample of the 87 participants and test-retest reliability sample of the 25 participants using t and chi-square tests. The psychometric properties of the driving tasks retained in the NPDI were assessed in terms of the three driving task performance levels in the Michon model (ie, strategic, tactical, and operational levels). The external panel categorized each driving task of the NPDI into one of the three driving performance levels. A primary driving task level was decided, in which the expert agreement was at least 50%.
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The responses of the 87 participants to the symptom section of the NPDI were analyzed descriptively. All statistical analyses were performed using SPSS version 19.0 (IBM Corporation, Somers, NY, USA). Significance level was set at less than .05. Results The participants with chronic WAD reported moderate levels of persisting neck pain and disability as reflected in the NDI score (Table 1). There were no significant differences in demographic data between the total sample of the 105 participants and test-retest reliability sample of the 25 participants (pO.05). Bilateral and unilateral upper limb symptoms were reported by 29% and 13% of the 87 participants, respectively. Such levels of neck pain and disability and widespread symptoms are not uncommon in those with chronic WAD [19–23]. Thus, our sample was representative of the chronic WAD population. Eight of the 20 driving tasks were excluded from the preliminary NPDI as they had more than 40% NA responses and/or flooring effects (Table 4). In the assessment of the internal consistency, no driving task was excluded. Consequently, 12 driving tasks remained in the NPDI (Table 4) with Cronbach a of 0.80, demonstrating good internal consistency [24]. The mean (standard deviation) scores from the 87 participants were 27.4% (18.0) for the 12-item NPDI and 4.9 (2.7) for the NRS of perceived driving difficulty. The NPDI scores
Table 4 Driving tasks refined in Phase 2 Descriptive analysis Driving tasks
NA (%)
Flooring effect* (%)
Anticipating potential risks (eg, pedestrians and cyclists) Braking suddenlyz Changing gears Changing lanesz Checking blind spotsz Controlling the steering wheel with both hands Driving at duskz Driving in bad weather conditions (eg, rain)z Driving for less than 30 min Driving for more than 1 hz Driving near (your) accident sitez Driving on a bumpy roadz Driving with passengers Judging the distance in front Merging on expresswaysz Night drivingz Reading traffic signs while driving Reversingz Turning the steering wheel quicklyz Visually tracking moving objects (eg, other cars)
5 7 48 0 0 1 6 1 1 3 6 5 1 3 5 3 2 0 5 2
57 47 64 22 16 69 48 29 62 24 38 40 52 56 29 46 58 24 48 53
NA, not applicable. * Ratio of people who selected Score 0 to those who selected except NA. y Ratio of people who selected Score 4 to those who selected except NA. z The 12 driving tasks that were retained for the Neck Pain Driving Index (final version).
Ceiling effecty (%) 0 1 2 0 1 3 1 1 0 1 4 4 1 1 3 1 0 3 3 0
Retained after the descriptive analysis
Retained after improvement of internal consistency
U
U
U U
U U
U U
U U
U U U
U U U
U U
U U
U U
U U
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Table 5 Distribution of the external panel opinions regarding psychometric properties of each driving task relating to the Michon model in the Neck Pain Driving Index Driving tasks Braking suddenly Changing lanes Checking blind spots Driving at dusk Driving in bad weather conditions (eg, rain) Driving for more than 1 h Driving near (your) accident site Driving on a bumpy road Merging on expressways Night driving Reversing Turning the steering wheel quickly
Strategic (%)
Tactical (%)
Operational (%)
0 13 7 73* 33
40 53* 67* 27 67*
60* 33 27 0 0
87* 33 67* 20 0 40 0
13 67* 27 80* 87* 60* 27
0 0 7 0 13 0 73*
* Primary driving task level with at least 50% agreement.
ranged from 0% to 79.5%. They demonstrated a moderate correlation [25] with the NRS of perceived driving difficulty (r50.51; p!.01) and a strong correlation [25] with the total NDI score (r50.80; p!.01). There was a significant correlation (intraclass correlation coefficient, 0.73; p!.01) between the NPDI scores gained on the two occasions. Table 5 displays the distribution of the external panel’s opinions regarding the psychometric property of each driving task in the NPDI. All 12 driving tasks could be categorized into one of the three driving task performance levels of the Michon model. Table 6 shows the distribution of responses of the driving tasks in the NPDI (first administration). The three driving tasks with the greatest proportion of scores for moderate or great difficulty were driving for more than 1 hour, checking blind spots and reversing. Table 7 displays the distribution of the 87 whiplash participants’ responses to the symptom section of the NPDI.
Headache, neck pain, stress/anxiety, and a lack of ability to move the neck quickly were reported to adversely affect driving ‘‘greatly’’ in at least 20% of cases.
Discussion This study developed the NPDI via a comprehensive process including assessments of the content validity, flooring and ceiling effects, and internal consistency. The acceptable validity and reliability of the 12-item NPDI were confirmed by evaluating the convergent validity and testretest reliability. The NPDI retained the three driving tasks that are the most troublesome for individuals with chronic WAD (ie, driving for more than 1 hour, checking blind spots, and reversing) [3], which are not included fully in other driving questionnaires. In addition, these three driving tasks had the greatest proportion of moderate or great difficulty scores. This further supports the content validity of the NPDI for the assessment of perceived driving difficulty in the chronic whiplash population and the need for a specific questionnaire for this population. The NPDI is the first questionnaire to categorize driving tasks within a hierarchical framework, the Michon model in this instance [8,9]. Such categorization is useful to analyze which conditions contribute to driving difficultly. The 12 driving tasks of the NPDI include three driving tasks at the strategic, seven at the tactical, and two at the operational levels. A top-down influence generally applies during normal driving, and a bottom-up influence applies in unexpected situations [9,10]. People with greater perceived difficulty in driving tasks at the strategic level may cope with their difficult tasks by modifying driving behaviors. For example, those who perceive difficulty driving for more than 1 hour could take regular breaks to reduce their continuous driving time. However, such strategies cannot be used for driving tasks at the operational level, which are essential
Table 6 Distribution of responses of the 87 participants with chronic whiplash-associated disorders to the driving task section of the Neck Pain Driving Index at the first administration Driving tasks*
NA (%)
No difficulty (%)
Slight difficulty (%)
Moderate difficulty (%)
Great difficulty (%)
Avoiding (%)
Driving for more than 1 h Checking blind spots Reversing Driving near (your) accident site Changing lanes Braking suddenly Driving in bad weather conditions (eg, rain) Merging on expressways Driving on a bumpy road Night driving Turning the steering wheel quickly Driving at dusk
3 0 0 6 0 7 1 5 5 3 5 6
23 16 24 36 22 44 29 28 38 45 46 45
28 41 36 25 46 25 40 38 36 32 34 36
34 29 26 16 23 20 22 21 13 10 8 9
10 13 11 14 9 3 7 7 6 8 5 3
1 1 2 3 0 7 1 2 3 1 2 1
NA, not applicable (a driving task has not been undertaken because of reasons that are different from my injury); avoiding, a driving task has not been undertaken because of my injury. * The driving tasks are listed in hierarchy from greatest to least based on the proportion of those with ‘‘moderate difficulty’’ with that task or more.
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Table 7 Distribution of responses of the 87 participants with chronic whiplash-associated disorders to the symptom section of the Neck Pain Driving Index at the first administration Symptoms*
NA (%)
Not at all (%)
Slight (%)
Moderate (%)
Great (%)
Unable to move your head quickly Neck pain Limited neck movement Headache Stress/anxiety Fearfulness Fatigue Difficulty concentrating Dizziness Arm pain Nausea
10 3 6 11 14 21 16 18 34 34 37
7 6 9 13 14 17 15 16 23 15 30
28 30 37 31 31 31 36 37 21 31 15
31 39 26 24 21 15 21 18 15 14 15
24 22 22 21 21 16 13 10 7 6 3
NA, not applicable (a symptom is not experienced); not at all, a symptom does not adversely affect driving at all; slight, a symptom adversely affects driving slightly; moderate, a symptom adversely affects driving moderately; great, a symptom adversely affects driving greatly. * Symptoms are listed in hierarchy from greatest to least based on of the proportion of those with ‘‘great difficulty.’’
to ensure road safety. Unexpected events may happen even in those who drive safely and perform driving tasks perfectly in the strategic and tactical levels. Thus, people with difficulty at the operational level may be at greater risk of subsequent accidents than those with difficulty at the strategic level. However, such associations between perceived driving difficulty and risk of a subsequent accident require further investigation. The risk of a subsequent accident can be assessed with the use of a driving simulator because on-road assessments may be too hazardous for those who may have impaired driving. Another way of assessing the risk of a subsequent accident is by using the Driving Behavior Questionnaire [26,27], which is a self-rating questionnaire of driving behaviors. It would be anticipated that those with higher levels of perceived driving difficulty would have increased frequency of driving errors, which increase the risk of a subsequent accident [26]. Therefore, it is of interest to investigate if there are significant correlations between the frequency of driving behaviors known to increase the risk of a subsequent accident [26,27], the total score of the NPDI, and scores of each hierarchical level of the NPDI. Thus, the NPDI can also be a foundation for further investigations of driving safety in the chronic whiplash population. The NPDI can also offer the clinician an opportunity to identify symptoms that may adversely affect driving. This study demonstrated that headache, neck pain, stress/anxiety, and a lack of ability to move the neck quickly were frequently nominated as symptoms adversely affecting driving in our chronic WAD group. The presence of pain and/or stress/anxiety adversely affects cognitive skills [28–31], which is one of the three factors necessary for safe driving [32]. Adequate physical functions and perception are the other two factors essential for safe driving [32]. A reduced ability to move the neck quickly would affect both these factors. Thus, driving performance and safety may be threatened in those with chronic WAD. Further studies are necessary to investigate if driving performance is impaired in individuals with chronic WAD.
The necessity for the NPDI could be questioned as there was a strong correlation between it and the NDI. This is not surprising as the construct of the NDI (ie, disability due to neck pain) is associated with that of the NPDI (ie, perceived difficulty in driving), and the NDI includes an item regarding driving. However, the correlation does not indicate that the NDI can be used as a proxy for understanding disability due to driving in those with chronic WAD. As mentioned previously, the NPDI provides not only information about the magnitude of perceived driving difficulty but also, as well, the possible implications for driving safety, which the NDI does not. It would also be unreasonable to make generalizations about driving safety using only one item from a scale not designed with a focus on driving. There are three possible limitations to this study. First, the NPDI cannot contribute to clinical decision making at this time, but rather, its development provides a foundation for further clinically relevant investigations such as the capacity of the NPDI to predict actual driving performance and its relationship to the risk of a subsequent car accident. Second, we did not question participants about their compensation or litigation status. However, we contend that their status would not influence their responses as the participants were volunteers and received no feedback or action from us in relation to their survey scores. Thus, there was no benefit to them in feigning responses. Also of note is the recent systematic review by Spearing and Connelly [33], which suggests that the case for compensation affecting health outcomes in whiplash is not strong. Third, the validity and reliability of the NPDI was confirmed in this study, but other robust methodologies could have been used. For example, a factor analysis could further examine construct validity, and a Rasch analysis could examine unidimensionality and targeting of the NPDI in the chronic whiplash population. Future research could change the weight of rating scales to investigate the NPDI’s predictable ability for risk of a subsequent accident. Such methods require larger sample sizes than those used in this study.
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Conclusion This study developed the NPDI to assess the degree of perceived driving difficulty in the chronic whiplash population. The reliability and validity of the NPDI were shown with the assessment of the content validity of all driving tasks, flooring and ceiling effects, internal consistency, convergent validity, and test-retest reliability. The NPDI is the first self-rating questionnaire to provide specific information about the level of perceived driving difficulty and information of the hierarchical model of driving, which could have implications for driving safety. The NPDI also contains a supplementary section on symptoms that may adversely affect driving and has the content validity. Thus, the NPDI can be a good tool to open discussions on driving difficulties between clinicians and people with chronic WAD and opens avenues for further research to understand the impact of perceived difficulties on driving performance. Acknowledgments The authors acknowledge all the participants for contributing their time.
Supplementary data To access the supplementary data accompanying this article, visit the online version of The Spine Journal at www.TheSpineJournalOnline.com, and at doi:10.1016/j. spinee.2012.09.053. References [1] Pereira MJ, Jull GA, Treleaven JM. Self-reported driving habits in subjects with persistent whiplash-associated disorder: relationship to sensorimotor and psychologic features. Arch Phys Med Rehabil 2008;89:1097–102. [2] Hoving JL, O’Leary EF, Niere KR, et al. Validity of the neck disability index, Northwick Park neck pain questionnaire, and problem elicitation technique for measuring disability associated with whiplash-associated disorders. Pain 2003;102:273–81. [3] Takasaki H, Johnston V, Treleaven J, et al. Driving with a chronic whiplash-associated disorder: a review of patients’ perspectives. Arch Phys Med Rehabil 2011;92:106–10. [4] Owsley C, Stalvey B, Wells J, Sloane ME. Older drivers and cataract: driving habits and crash risk. J Gerontol A Biol Sci Med Sci 1999;54: M203–11. [5] Cohen HS, Wells J, Kimball KT, Owsley C. Driving disability and dizziness. J Safety Res 2003;34:361–9. [6] George S, Clark M, Crotty M. Development of the Adelaide driving self-efficacy scale. Clin Rehabil 2007;21:56–61. [7] Van Rijn LJ, Wilhelm H, Emesz M, et al. Relation between perceived driving disability and scores of vision screening tests. Br J Ophthalmol 2002;86:1262–4. [8] Michon JA. A critical view of driver behaviour models: what do we know, what should we do. In: Evans L, Laoschwing RC, eds. Human behaviour and traffic safety. New York: Plenum Press, 1985:485–520. [9] Van Der Molen HH, Botticher AMT. A hierarchical risk model for traffic participants. Ergonomics 1988;31:537–55.
[10] Schaap TW, Van Der Horst ARA, Van Arem B, Brookhuis KA. Drivers’ reactions to sudden braking by lead car under varying workload conditions; towards a driver support system. IET INTELL TRANSP SY 2008;2:249–57. [11] Wynd CA, Schmidt B, Schaefer MA. Two quantitative approaches for estimating content validity. West J Nurs Res 2003;25:508–18. [12] Polit DF, Beck CT. The content validity index: are you sure you know what’s being reported? Critique and recommendations. Res Nurs Health 2006;29:489–97. [13] Lynn MR. Determination and quantification of content validity. Nurs Res 1986;35:382–5. [14] Davis LL. Instrument review: getting the most from a panel of experts. Appl Nurs Res 1992;5:194–7. [15] Vernon H, Mior S. The Neck Disability Index: a study of reliability and validity. J Manipulative Physiol Ther 1991;14:409–15. [16] Westaway MD, Stratford PW, Binkley JM. The patient-specific functional scale: validation of its use in persons with neck dysfunction. J Orthop Sports Phys Ther 1998;27:331–8. [17] Nieto R, Miro J, Huguet A. Disability in subacute whiplash patients: usefulness of the neck disability index. Spine 2008;33:E630–5. [18] Pinfold M, Niere KR, O’Leary EF, et al. Validity and internal consistency of a whiplash-specific disability measure. Spine 2004;29: 263–8. [19] Bunketorp L, Nordholm L, Carlsson J. A descriptive analysis of disorders in patients 17 years following motor vehicle accidents. Eur Spine J 2002;11:227–34. [20] Guez M, Hildingsson C, Nasic S, Toolanen G. Chronic low back pain in individuals with chronic neck pain of traumatic and nontraumatic origin: a population-based study. Acta Orthop 2006;77: 132–7. [21] Ihlebeak C, Odegaard A, Vikne J, et al. Subjective health complaints in patients with chronic whiplash associated disorders (WAD). Relationships with physical, psychological, and collision associated factors. Norsk Epidemiologi 2006;16:119–26. [22] Radanov BP, Sturzenegger M, Di Stefano G. Long-term outcome after whiplash injury. A 2-year follow-up considering features of injury mechanism and somatic, radiologic, and psychosocial findings. Medicine (Baltimore) 1995;74:281–97. [23] Sterling M, Kenardy J, Jull G, Vicenzino B. The development of psychological changes following whiplash injury. Pain 2003;106: 481–9. [24] George D, Mallery P. SPSS for Windows step-by-step: a simple guide and reference, 13.0 update. Boston: Allyn & Bacon, 2005. [25] Andresen EM. Criteria for assessing the tools of disability outcomes research. Arch Phys Med Rehabil 2000;81:S15–20. [26] Parker D, West R, Stradling S, Manstead AS. Behavioural characteristics and involvement in different types of traffic accident. Accid Anal Prev 1995;27:571–81. [27] de Winter JC, Dodou D. The Driver Behaviour Questionnaire as a predictor of accidents: a meta-analysis. J Safety Res 2010;41:463–70. [28] Kuhajda MC, Thorn BE, Klinger MR, Rubin NJ. The effect of headache pain on attention (encoding) and memory (recognition). Pain 2002;97:213–21. [29] Pais-Vieira M, Mendes-Pinto MM, Lima D, Galhardo V. Cognitive impairment of prefrontal-dependent decision-making in rats after the onset of chronic pain. Neuroscience 2009;161:671–9. [30] Eysenck MW, Derakshan N, Santos R, Calvo MG. Anxiety and cognitive performance: attentional control theory. Emotion 2007;7: 336–53. [31] Causer J, Holmes PS, Smith NC, Williams AM. Anxiety, movement kinematics, and visual attention in elite-level performers. Emotion 2011;11:595–602. [32] Austroads. Assessing fitness to drive. 3rd ed. Sydney, NSW: Austroads, 2003. [33] Spearing NM, Connelly LB. Is compensation ‘‘bad for health’’? A systematic meta-review. Injury 2011;42:15–24.
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Supplementary Appendix Neck Pain Driving Index (NPDI) The purpose of this questionnaire is to better understand the degree of your perceived difficulty in driving. I. Driving task section During the past 3 months, have you experienced the following driving tasks? If yes: rate the difficulty with (U) in the box below. If no: (U) in the box below the reason for not doing so. This may be because of problems relevant to your injury or for reasons not related to your injury. No Strategic level
Not because of my injury
Yes Because of my injury
No difficulty
Slight difficulty
Moderate difficulty
Great difficulty
Slight difficulty
Moderate difficulty
Great difficulty
Slight difficulty
Moderate difficulty
Great difficulty
Driving at dusk Driving for more than 1 hour Driving on a bumpy road No Tactical level
Not because of my injury
Yes Because of my injury
No difficulty
Changing lanes Checking blind spots Driving in bad weather conditions (eg, rain) Driving near (your) accident site Merging on expressways Night driving Reversing No Operational level
Not because of my injury
Yes Because of my injury
No difficulty
Braking suddenly Turning the steering wheel quickly Note: Not because of my injury (not applicable; NA), no difficulty (Score 0), slight difficulty (Score 1), moderate difficulty (Score 2), great difficulty (Score 3), because of my injury (Score 4). Excluding the NA tasks, the score is summed and expressed as a percentage of the total score. A score of 100% indicates the greatest perceived driving difficulty while 0% indicates no perceived driving difficulty.
II. Symptom section During the past 3 months, have you experienced the following symptoms? If yes: rate to what extent the following symptoms have adversely affected your driving ability with (U) in the box below. If no: (U) in the box below. How have they adversely affected your driving? Symptoms Arm pain Difficulty concentrating Dizziness Fatigue Fearfulness Headache Limited neck movement Nausea Neck pain Stress/anxiety Unable to move your head quickly
No
Not at all
Slightly
Moderately
Greatly
Clinical Study
The Neck Pain Driving Index (NPDI) for chronic whiplash-associated disorders: development, reliability, and validity assessment Hiroshi Takasaki, MS*, Venerina Johnston, PhD, Julia M. Treleaven, PhD, Gwendolen A. Jull, PhD NHMRC Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, Division of Physiotherapy, School of Health and Rehabilitation Science, The University of Queensland, Brisbane, Queensland 4072, Australia Received 29 July 2011; revised 13 March 2012; accepted 25 September 2012
Abstract
BACKGROUND CONTEXT: Driving is a functional complaint of many individuals with chronic whiplash-associated disorders (WAD). Current driving scales do not include the most troublesome driving tasks for this group, which suggests that a new tool is required to assess perceived driving difficulty in this population. PURPOSE: To develop a Neck Pain Driving Index (NPDI) to assess the degree of perceived driving difficulty for individuals with chronic WAD and evaluate the reliability and validity of the NPDI. STUDY DESIGN: Descriptive/survey. PATIENT SAMPLE: An external panel of 15 researchers/clinicians and 87 participants with chronic WAD. OUTCOME MEASURES: The NPDI and a 0 to 10 numeric rating scale (NRS) of perceived driving difficulty (0, no difficulty and 10, maximum difficulty). METHODS: Phase 1 included the construction of a preliminary NPDI and content validity assessment of question items by a 15-member external panel. Comprehension was evaluated by seven participants with chronic WAD. In Phase 2, the final version of the NPDI was developed via descriptive analysis and assessment of internal consistency using responses of 87 participants with chronic WAD. Subsequently, the convergent validity was assessed using NRS scores. Test-retest reliability at 1 month was investigated in 25 of the 87 participants. Psychometric properties of the driving tasks in the final NPDI were categorized by the external panel, based on the hierarchal Michon model of driving task performance levels. An additional symptom section was developed to better understand the reasons for driving difficulties. RESULTS: The final NPDI included 12 driving tasks, which scored at least 80% on the content validity index (CVI), ensuring content validity. The NPDI demonstrated good internal consistency (a50.80), convergent validity (r50.51; p!.01), and test-retest reliability (intraclass correlation coefficient, 0.73; p!.01). As a result of the assessment of psychometric properties, driving tasks were categorized into the strategic (n53), tactical (n57), and operational (n52) levels in the Michon model. The content validity of 11 symptoms (CVI $80%) was established by the external panel. CONCLUSIONS: The NPDI was developed to assess the degree of perceived driving difficulty in the chronic whiplash population. Reliability and validity of the NPDI were ensured. The NPDI can be the entry point for discussions on driving difficulties between clinicians and patients with chronic WAD. Ó 2012 Elsevier Inc. All rights reserved.
Keywords:
Automobile driving; Neck pain; Questionnaire; Reliability and validity; Whiplash injuries
FDA device/drug status: Not applicable. Author disclosures: HT: Nothing to disclose. VJ: Nothing to disclose. JMT: Nothing to disclose. GAJ: Nothing to disclose. * Corresponding author. NHMRC Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, Division of Physiotherapy, School 1529-9430/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.spinee.2012.09.053
of Health and Rehabilitation Science, The University of Queensland, Brisbane, Queensland 4072, Australia. Tel.: (61) 7-3365-2275; fax: (61) 7-3365-1622. E-mail address: [email protected] (H. Takasaki)
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Introduction Driving is a functional task with which many people with chronic whiplash-associated disorders (WAD) report various difficulties [1–3], including a perceived reduction in their driving ability [3]. Thus, it is important to evaluate perceived driving difficulty in the chronic whiplash population to serve as a platform to understand the driving performance and safety in this group. Questionnaires have been developed to assess driving difficulty in specific populations, including those with visual impairments, stroke, advanced age, and/or dizziness [1,4– 7]. Recently, Takasaki et al. [3] found that the most troublesome driving tasks reported by individuals with chronic WAD were checking blind spots, prolonged driving, and reversing/reverse parking. However, these three driving tasks are not included in the current questionnaires. This indicates a need to develop a specific questionnaire to assess the degree of perceived driving difficulty in the chronic whiplash population and indeed those with neck pain disorders. When developing a new questionnaire, consideration should be given to the specific driving tasks causing difficulties and reasons why these are difficult. Additional information on symptoms that may adversely affect driving would offer the clinician an opportunity to open discussion on driving in the chronic whiplash population. Furthermore, the specific driving tasks that may be difficult should be considered in relation to a hierarchal model of driving tasks such as the Michon model [8,9]. This model’s hierarchy is the strategic, tactical, and operational levels. The strategic level refers to the planning of general driving such as driving time and route [8,9]. The tactical level relates to the observation/selection of signals and planning of actions depending on traffic conditions. The operational level refers to specific and automatic actions such as turning the steering wheel and changing gears. Normal driving is generally performed with a topdown influence [9,10]. For example, to drive in an environment with constantly changing traffic conditions such as city driving (strategic level) requires significant mental effort. This limits available resources for tasks such as checking mirrors (tactical level). Insufficient observation skills increase chances of unexpected situations that may require sudden braking and quick steering control (operational level). Thus, a questionnaire that can assess driving difficulty over these three levels would be useful. However, to date, there has been no questionnaire structured in this way. The purpose of this study was twofold. The primary aim was to develop a questionnaire—the Neck Pain Driving Index (NPDI)—to assess the degree of perceived driving difficulty in the chronic whiplash population. The second aim was to establish the reliability and validity of the NPDI.
Methods The NPDI was developed via a two-phase process, which included the development of a preliminary version
Context Assessment of functional limitations allows treating physicians to better understand a patient’s current status and response to treatment. In this article, the authors present a questionnaire affording such assessment regarding driving and whiplash-associated disorders (WAD). Contribution The authors provide an early attempt to establish a reliable and valid method of assessing self-perceived driving impairment. Their analysis found good test-retest reliability and apparent validity of self-reported perceived impairment in a small number of test subjects, including subjects in litigation. Implication Although testing this index against external validation remains to be performed, validated measures are vital for the assessment of outcomes. Disease/functionspecific measures, such as this one, if further developed and independently validated, may allow treating physicians to identify prognostic subgroups or interventions that might specifically address an important aspect of a patient’s problem. —The Editors
followed by the development of a final version (Figure). This study was approved by the institutional human medical ethics committee. All participants provided informed consent. Phase 1: Development of a preliminary NPDI Question items (driving tasks and symptoms) for the NPDI were generated, and the content validity of each question item was assessed by an external panel before administering a preliminary draft of the NPDI to a sample of individuals with chronic WAD for readability and comprehension. Participants For the external panel, 18 people were approached, on the basis of their research and publication record and/or clinical experience in the field of WAD, to participate in a study to establish the content validity of the preliminary draft of the NPDI. Fifteen people agreed to join an external panel and comprised 11 researchers and four clinicians. The external panel came from the following disciplines: medical doctor (1), physiotherapy (13), and chiropractic (1). The external panel had a mean (standard deviation) research/ clinical experience with whiplash of 23.3 (8.9) years.
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disorders). Seven chronic WAD patients participated in Phase 1. Their characteristics are presented in Table 1.
Figure. The development of a two-phase NPDI. 1Assessed using data from external panel. 2Assessed using data from patients with chronic WAD who were recruited from a whiplash clinic in a local university. 3Assessed using data from the chronic whiplash population in Australia. 4Included the flooring and ceiling effects. NPDI, Neck Pain Driving Index; WAD, whiplash-associated disorders.
Chronic WAD patients were recruited from a university whiplash clinic to provide feedback on English expression and comprehension of the preliminary draft of the NPDI. Inclusion criteria were currently driving and aged between 20 and 60 years and neck pain for at least 3 months to 5 years after whiplash injury. Patients were excluded if they had a cervical fracture or dislocation, potential head injury including loss of consciousness at the time of the whiplash injury, upper or lower limb fractures/injuries, or any comorbid medical problems that could affect driving performance (eg, neurologic, cardiovascular, respiratory, and visual
Procedure Phase 1 was completed in three steps. First, possible driving tasks and symptoms, which may be important for the assessment of perceived driving difficulty, were generated from a review of the literature and discussions between the authors. A first draft of a preliminary NPDI was then developed, which included 27 driving tasks and eight symptoms (Tables 2 and 3). Second, the content validity of each driving task and symptom was examined by the external panel. The use of both the content validity index (CVI) and multirater kappa coefficient of agreement provides more rigorous assessment of the content validity than the use of the CVI alone [11], but the use of both may be too restrictive for the developmental stage of a new questionnaire. Thus, this study used the CVI to assess the content validity in the first phase. The external panel rated the relevance of the driving tasks and symptoms to driving difficulty for individuals with chronic WAD using a four-point scale: not relevant, somewhat relevant, quite relevant, and very relevant in Draft 1 of the preliminary NPDI. The CVI, which is the proportion of driving tasks and symptoms receiving a rating of ‘‘quite relevant’’ or ‘‘very relevant,’’ was calculated. Driving tasks and symptoms with less than 80% in the CVI were rejected from the item list because of the unacceptable level of agreement [12–14]. As a result, 12 driving tasks were rejected from the item list (Tables 2 and 3). The external panel was also requested to nominate additional driving tasks and symptoms not included in Draft 1 that might be related to driving difficulty for individuals with chronic WAD. In response, a second draft of the preliminary NPDI was constructed. It included an additional six driving tasks and nine symptoms and was sent to the same external panel for reassessment of the CVI. The review of the CVI of the second draft resulted in the exclusion of one driving task and six symptoms (Tables 2 and 3). Consequently, a third draft of the preliminary NPDI was written, comprising 20 driving tasks and 12 symptoms (Tables 2 and 3). In the third step, seven chronic WAD patients reviewed Draft 3 of the preliminary NPDI and provided feedback on wording and English expression for the driving tasks
Table 1 Characteristics of the participants with chronic whiplash-associated disorders in Phases 1 and 2 Phase 2 Variables
Phase 1 (n57)
Total sample (N587)
Reliability study sample (n525)
Age, mean (SD), y Driving experience, mean (SD), y Total kilometers driven per week, mean (SD), km Time since accident, mean (SD), mo NDI, mean (SD) Female, n (%)
31.9 13.9 148.6 13.7 55.4 6
38.4 19.5 252.9 21.5 37.5 69
41.6 22.7 286.4 20.7 38.2 21
SD, standard deviation; NDI, The Neck Disability Index.
(7.3) (7.3) (132.6) (11.0) (8.0) (86)
(11.5) (11.5) (278.6) (16.7) (16.4) (80)
(12.7) (12.8) (283.1) (16.7) (18.9) (84)
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Table 2 Content validity of driving tasks as assessed by the 15-member external panel
Driving tasks Accelerating suddenly Anticipating potential risks (eg, pedestrians and cyclists)* Braking suddenly* Changing lanes* Checking blind spots* Driving alone Driving an unfamiliar car (eg, a rental car and spouse’s car) Driving in bad weather conditions (eg, rain)* Driving in unfamiliar areas Driving for less than 30 min* Driving for more than 1 h* Driving near (your) accident site* Driving on a bumpy road* Driving on a freeway Holding conversations while driving Judging distance in the rear view mirror Judging the distance in front* Merging on expressways* Navigating roundabouts Night driving* Operating CDs/radio while driving Peak/rush hour driving Reading traffic signs while driving* Reversing* Turning at intersections without traffic lights Turning right oncoming traffic Turning the steering wheel quickly* Changing gears* Controlling the steering wheel with both hands* Driving at dusk* Driving in variable light (eg, in and out of a tunnel) Driving with passengers* Visually tracking moving objects (eg, other cars)*
Initially listed U U U U U U U U U U U U U U U U U U U U U U U U U U U
Accepted by the first content validity assessment
Added after the first content validity assessment
Accepted by the second content validity assessment
U U U U U U U U U
U U U U U U
U U U U U U
U U U U U
CVI (%) 73 93 93 93 93 73 60 100 73 80 93 93 87 73 40 73 87 87 73 87 60 73 87 100 73 73 93 80 80 80 73 80 100
Retained after pilot trial U U U U U U U U U
U U U U U U U U U U U
CVI, content validity index; CD, compact disc. * Driving tasks retained for the final draft of the preliminary Neck Pain Driving Index.
and symptoms, which resulted in vertigo and dizziness being combined. The final version of the preliminary NPDI included 20 driving tasks and 11 symptoms (Tables 2 and 3). Phase 2: Development of a final version of the NPDI The driving task section of the preliminary NPDI was the focus of the Phase 2 research. Procedures included the development of a final version of the NPDI via the assessment of flooring and ceiling effects and internal consistency of the 20 driving tasks of the preliminary NPDI and examination of the construct validity in particular the convergent validity, test-retest reliability, and psychometric properties of the driving tasks retained in the final version of the NPDI. The symptom section was additional and designed to assist the understanding of possible reasons for the driving difficulty. Data on symptoms retained (CVI $80% in Phase 1) were collected for descriptive purposes.
Participants Participants with chronic WAD were recruited through advertising in the popular press and in community practices in Australia from June 2010 to June 2011 to develop the final version of the NPDI. Participant inclusion and exclusion criteria were identical to Phase 1. Eighty-seven people with chronic WAD participated in Phase 2. In addition, 25 of the 87 participants agreed to participate in the assessment of test-retest reliability of the NPDI after a 1-month interval. The characteristics of primary and subset groups are presented in Table 1. The same external panel recruited in Phase 1 assessed the psychometric property of each driving task of the final version of the NPDI for their placement within the Michon model. Procedure A package of questionnaires was forwarded electronically or in hardcopy to the 87 participants with chronic WAD to examine the flooring and ceiling effects, internal consistency,
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Table 3 Content validity of symptoms as assessed by the 15-member external panel
Symptoms Arm pain* Difficulty concentrating* Fatigue* Headache* Limited neck movement* Neck pain* Stress/anxiety* Unable to move your head quickly* Dizziness* Depression Fearfulness* Irritable mood Limited trunk movement Muscle weakness Nausea* Tinnitus Vertigo
Initially listed
Accepted by the first content validity assessment
U U U U U U U U
U U U U U U U U
Added after the first content validity assessment
U U U U U U U U U
Accepted by the second content validity assessment
U
U U
CVI (%) 100 87 87 93 100 100 100 100 93 27 93 47 73 33 93 33 93
Retained after pilot trial U U U U U U U U U U
U
CVI, content validity index. * Symptoms retained for the final Neck Pain Driving Index.
convergent validity, and test-retest reliability of NPDI. The completed questionnaires were returned electronically or in a self-enclosed envelope. The questionnaires could be completed within 15 minutes. The package included the preliminary NPDI (driving task and symptom sections), a 0 to 10 numeric rating scale (NRS) of perceived driving difficulty, and the Neck Disability Index (NDI). One month later, the 25 participants completed the preliminary NPDI (driving task section) again to obtain data for the assessment of testretest reliability of the final version of the NPDI. The preliminary NPDI The construct of the preliminary NPDI requested respondents to rate the degree of difficulty in performing each driving task during the last 3 months on a four-point Likert scale: no difficulty (Score 0), slight difficulty (Score 1), moderate difficulty (Score 2), and great difficulty (Score 3). If the respondent had not undertaken a certain driving task, the options were either because of reasons not related to my injury (not applicable [NA]) or because of my injury (Score 4). Not applicable responses were excluded for item scoring. The respondents’ scores in each task were summed and expressed as a percentage of the total possible score. A score of 0% indicated no difficulty, whereas 100% indicated maximum perceived difficulty. The total score (percentage) was calculated for the items retained in the final version of the NPDI to examine the convergent validity and test-retest reliability. In the symptom section, respondents were asked to rate how much each symptom had adversely affected their driving ability during the last 3 months on a five-point scale: NA (if a symptom has not been experienced), does not affect driving at all, adversely affects driving slightly, adversely affects driving moderately, or adversely affects driving greatly.
Numeric Rating Scale of perceived driving difficulty Participants rated their perceived driving difficulty with a single question, ‘‘Overall have you had any difficulty driving following your injury?’’ on an NRS (0, no difficulty and 10, maximum difficulty). This scale was used to investigate the convergent validity of the final version of the NPDI. Neck Disability Index The NDI is a 10-item questionnaire assessing global disability due to neck pain, and although it includes one question regarding driving, it was not designed to specifically assess disability for driving [15]. Each item has six different assertions corresponding to scores of 0 to 5. The total score is expressed in percentiles with 100% being the highest level of disability associated with neck pain. The NDI has good concurrent validity [2,16,17] and internal consistency (a50.87) in the whiplash population [17]. Hence, this scale was used to investigate correlation to the final version of the NPDI and understand the characteristics of the participants in this study. Statistical procedures Responses from the 87 participants with chronic WAD in the driving task section of the preliminary NPDI were initially analyzed descriptively. Driving tasks were excluded from the item list when more than 40% of responses were NA. All remaining responses were examined for flooring and ceiling effects. A flooring or ceiling effect was considered when more than 50% of the responses (excluding NA scores) were the minimum (Score 0) or maximum (Score 4) response [18]. Driving tasks with flooring or ceiling effects were excluded.
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The internal consistency for driving tasks retained was computed with Cronbach a. Driving tasks were excluded from the item list when the hypothetical value of a was higher than the total value of a. From this analysis, the NPDI (ie, final version) was developed (see Supplementary Appendix). Data from the 87 participants for the NPDI and NRS were not normally distributed (Kolmogorov-Smirnov tests). Hence, the convergent validity was evaluated by calculating Spearman r between the score of the NPDI at the first administration of the preliminary NPDI and NRS of perceived driving difficulty. Spearman r was also used to examine the correlation between the scores of the NDI and first administration of the preliminary NPDI. The data of 25 participants from the driving tasks retained in the first and second administrations of the preliminary NPDI were normally distributed (Shapiro-Wilk tests). The test-retest reliability of the NPDI (1-month interval) was determined with the intraclass correlation coefficient. Demographic data were compared between the total sample of the 87 participants and test-retest reliability sample of the 25 participants using t and chi-square tests. The psychometric properties of the driving tasks retained in the NPDI were assessed in terms of the three driving task performance levels in the Michon model (ie, strategic, tactical, and operational levels). The external panel categorized each driving task of the NPDI into one of the three driving performance levels. A primary driving task level was decided, in which the expert agreement was at least 50%.
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The responses of the 87 participants to the symptom section of the NPDI were analyzed descriptively. All statistical analyses were performed using SPSS version 19.0 (IBM Corporation, Somers, NY, USA). Significance level was set at less than .05. Results The participants with chronic WAD reported moderate levels of persisting neck pain and disability as reflected in the NDI score (Table 1). There were no significant differences in demographic data between the total sample of the 105 participants and test-retest reliability sample of the 25 participants (pO.05). Bilateral and unilateral upper limb symptoms were reported by 29% and 13% of the 87 participants, respectively. Such levels of neck pain and disability and widespread symptoms are not uncommon in those with chronic WAD [19–23]. Thus, our sample was representative of the chronic WAD population. Eight of the 20 driving tasks were excluded from the preliminary NPDI as they had more than 40% NA responses and/or flooring effects (Table 4). In the assessment of the internal consistency, no driving task was excluded. Consequently, 12 driving tasks remained in the NPDI (Table 4) with Cronbach a of 0.80, demonstrating good internal consistency [24]. The mean (standard deviation) scores from the 87 participants were 27.4% (18.0) for the 12-item NPDI and 4.9 (2.7) for the NRS of perceived driving difficulty. The NPDI scores
Table 4 Driving tasks refined in Phase 2 Descriptive analysis Driving tasks
NA (%)
Flooring effect* (%)
Anticipating potential risks (eg, pedestrians and cyclists) Braking suddenlyz Changing gears Changing lanesz Checking blind spotsz Controlling the steering wheel with both hands Driving at duskz Driving in bad weather conditions (eg, rain)z Driving for less than 30 min Driving for more than 1 hz Driving near (your) accident sitez Driving on a bumpy roadz Driving with passengers Judging the distance in front Merging on expresswaysz Night drivingz Reading traffic signs while driving Reversingz Turning the steering wheel quicklyz Visually tracking moving objects (eg, other cars)
5 7 48 0 0 1 6 1 1 3 6 5 1 3 5 3 2 0 5 2
57 47 64 22 16 69 48 29 62 24 38 40 52 56 29 46 58 24 48 53
NA, not applicable. * Ratio of people who selected Score 0 to those who selected except NA. y Ratio of people who selected Score 4 to those who selected except NA. z The 12 driving tasks that were retained for the Neck Pain Driving Index (final version).
Ceiling effecty (%) 0 1 2 0 1 3 1 1 0 1 4 4 1 1 3 1 0 3 3 0
Retained after the descriptive analysis
Retained after improvement of internal consistency
U
U
U U
U U
U U
U U
U U U
U U U
U U
U U
U U
U U
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Table 5 Distribution of the external panel opinions regarding psychometric properties of each driving task relating to the Michon model in the Neck Pain Driving Index Driving tasks Braking suddenly Changing lanes Checking blind spots Driving at dusk Driving in bad weather conditions (eg, rain) Driving for more than 1 h Driving near (your) accident site Driving on a bumpy road Merging on expressways Night driving Reversing Turning the steering wheel quickly
Strategic (%)
Tactical (%)
Operational (%)
0 13 7 73* 33
40 53* 67* 27 67*
60* 33 27 0 0
87* 33 67* 20 0 40 0
13 67* 27 80* 87* 60* 27
0 0 7 0 13 0 73*
* Primary driving task level with at least 50% agreement.
ranged from 0% to 79.5%. They demonstrated a moderate correlation [25] with the NRS of perceived driving difficulty (r50.51; p!.01) and a strong correlation [25] with the total NDI score (r50.80; p!.01). There was a significant correlation (intraclass correlation coefficient, 0.73; p!.01) between the NPDI scores gained on the two occasions. Table 5 displays the distribution of the external panel’s opinions regarding the psychometric property of each driving task in the NPDI. All 12 driving tasks could be categorized into one of the three driving task performance levels of the Michon model. Table 6 shows the distribution of responses of the driving tasks in the NPDI (first administration). The three driving tasks with the greatest proportion of scores for moderate or great difficulty were driving for more than 1 hour, checking blind spots and reversing. Table 7 displays the distribution of the 87 whiplash participants’ responses to the symptom section of the NPDI.
Headache, neck pain, stress/anxiety, and a lack of ability to move the neck quickly were reported to adversely affect driving ‘‘greatly’’ in at least 20% of cases.
Discussion This study developed the NPDI via a comprehensive process including assessments of the content validity, flooring and ceiling effects, and internal consistency. The acceptable validity and reliability of the 12-item NPDI were confirmed by evaluating the convergent validity and testretest reliability. The NPDI retained the three driving tasks that are the most troublesome for individuals with chronic WAD (ie, driving for more than 1 hour, checking blind spots, and reversing) [3], which are not included fully in other driving questionnaires. In addition, these three driving tasks had the greatest proportion of moderate or great difficulty scores. This further supports the content validity of the NPDI for the assessment of perceived driving difficulty in the chronic whiplash population and the need for a specific questionnaire for this population. The NPDI is the first questionnaire to categorize driving tasks within a hierarchical framework, the Michon model in this instance [8,9]. Such categorization is useful to analyze which conditions contribute to driving difficultly. The 12 driving tasks of the NPDI include three driving tasks at the strategic, seven at the tactical, and two at the operational levels. A top-down influence generally applies during normal driving, and a bottom-up influence applies in unexpected situations [9,10]. People with greater perceived difficulty in driving tasks at the strategic level may cope with their difficult tasks by modifying driving behaviors. For example, those who perceive difficulty driving for more than 1 hour could take regular breaks to reduce their continuous driving time. However, such strategies cannot be used for driving tasks at the operational level, which are essential
Table 6 Distribution of responses of the 87 participants with chronic whiplash-associated disorders to the driving task section of the Neck Pain Driving Index at the first administration Driving tasks*
NA (%)
No difficulty (%)
Slight difficulty (%)
Moderate difficulty (%)
Great difficulty (%)
Avoiding (%)
Driving for more than 1 h Checking blind spots Reversing Driving near (your) accident site Changing lanes Braking suddenly Driving in bad weather conditions (eg, rain) Merging on expressways Driving on a bumpy road Night driving Turning the steering wheel quickly Driving at dusk
3 0 0 6 0 7 1 5 5 3 5 6
23 16 24 36 22 44 29 28 38 45 46 45
28 41 36 25 46 25 40 38 36 32 34 36
34 29 26 16 23 20 22 21 13 10 8 9
10 13 11 14 9 3 7 7 6 8 5 3
1 1 2 3 0 7 1 2 3 1 2 1
NA, not applicable (a driving task has not been undertaken because of reasons that are different from my injury); avoiding, a driving task has not been undertaken because of my injury. * The driving tasks are listed in hierarchy from greatest to least based on the proportion of those with ‘‘moderate difficulty’’ with that task or more.
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Table 7 Distribution of responses of the 87 participants with chronic whiplash-associated disorders to the symptom section of the Neck Pain Driving Index at the first administration Symptoms*
NA (%)
Not at all (%)
Slight (%)
Moderate (%)
Great (%)
Unable to move your head quickly Neck pain Limited neck movement Headache Stress/anxiety Fearfulness Fatigue Difficulty concentrating Dizziness Arm pain Nausea
10 3 6 11 14 21 16 18 34 34 37
7 6 9 13 14 17 15 16 23 15 30
28 30 37 31 31 31 36 37 21 31 15
31 39 26 24 21 15 21 18 15 14 15
24 22 22 21 21 16 13 10 7 6 3
NA, not applicable (a symptom is not experienced); not at all, a symptom does not adversely affect driving at all; slight, a symptom adversely affects driving slightly; moderate, a symptom adversely affects driving moderately; great, a symptom adversely affects driving greatly. * Symptoms are listed in hierarchy from greatest to least based on of the proportion of those with ‘‘great difficulty.’’
to ensure road safety. Unexpected events may happen even in those who drive safely and perform driving tasks perfectly in the strategic and tactical levels. Thus, people with difficulty at the operational level may be at greater risk of subsequent accidents than those with difficulty at the strategic level. However, such associations between perceived driving difficulty and risk of a subsequent accident require further investigation. The risk of a subsequent accident can be assessed with the use of a driving simulator because on-road assessments may be too hazardous for those who may have impaired driving. Another way of assessing the risk of a subsequent accident is by using the Driving Behavior Questionnaire [26,27], which is a self-rating questionnaire of driving behaviors. It would be anticipated that those with higher levels of perceived driving difficulty would have increased frequency of driving errors, which increase the risk of a subsequent accident [26]. Therefore, it is of interest to investigate if there are significant correlations between the frequency of driving behaviors known to increase the risk of a subsequent accident [26,27], the total score of the NPDI, and scores of each hierarchical level of the NPDI. Thus, the NPDI can also be a foundation for further investigations of driving safety in the chronic whiplash population. The NPDI can also offer the clinician an opportunity to identify symptoms that may adversely affect driving. This study demonstrated that headache, neck pain, stress/anxiety, and a lack of ability to move the neck quickly were frequently nominated as symptoms adversely affecting driving in our chronic WAD group. The presence of pain and/or stress/anxiety adversely affects cognitive skills [28–31], which is one of the three factors necessary for safe driving [32]. Adequate physical functions and perception are the other two factors essential for safe driving [32]. A reduced ability to move the neck quickly would affect both these factors. Thus, driving performance and safety may be threatened in those with chronic WAD. Further studies are necessary to investigate if driving performance is impaired in individuals with chronic WAD.
The necessity for the NPDI could be questioned as there was a strong correlation between it and the NDI. This is not surprising as the construct of the NDI (ie, disability due to neck pain) is associated with that of the NPDI (ie, perceived difficulty in driving), and the NDI includes an item regarding driving. However, the correlation does not indicate that the NDI can be used as a proxy for understanding disability due to driving in those with chronic WAD. As mentioned previously, the NPDI provides not only information about the magnitude of perceived driving difficulty but also, as well, the possible implications for driving safety, which the NDI does not. It would also be unreasonable to make generalizations about driving safety using only one item from a scale not designed with a focus on driving. There are three possible limitations to this study. First, the NPDI cannot contribute to clinical decision making at this time, but rather, its development provides a foundation for further clinically relevant investigations such as the capacity of the NPDI to predict actual driving performance and its relationship to the risk of a subsequent car accident. Second, we did not question participants about their compensation or litigation status. However, we contend that their status would not influence their responses as the participants were volunteers and received no feedback or action from us in relation to their survey scores. Thus, there was no benefit to them in feigning responses. Also of note is the recent systematic review by Spearing and Connelly [33], which suggests that the case for compensation affecting health outcomes in whiplash is not strong. Third, the validity and reliability of the NPDI was confirmed in this study, but other robust methodologies could have been used. For example, a factor analysis could further examine construct validity, and a Rasch analysis could examine unidimensionality and targeting of the NPDI in the chronic whiplash population. Future research could change the weight of rating scales to investigate the NPDI’s predictable ability for risk of a subsequent accident. Such methods require larger sample sizes than those used in this study.
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Conclusion This study developed the NPDI to assess the degree of perceived driving difficulty in the chronic whiplash population. The reliability and validity of the NPDI were shown with the assessment of the content validity of all driving tasks, flooring and ceiling effects, internal consistency, convergent validity, and test-retest reliability. The NPDI is the first self-rating questionnaire to provide specific information about the level of perceived driving difficulty and information of the hierarchical model of driving, which could have implications for driving safety. The NPDI also contains a supplementary section on symptoms that may adversely affect driving and has the content validity. Thus, the NPDI can be a good tool to open discussions on driving difficulties between clinicians and people with chronic WAD and opens avenues for further research to understand the impact of perceived difficulties on driving performance. Acknowledgments The authors acknowledge all the participants for contributing their time.
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Supplementary Appendix Neck Pain Driving Index (NPDI) The purpose of this questionnaire is to better understand the degree of your perceived difficulty in driving. I. Driving task section During the past 3 months, have you experienced the following driving tasks? If yes: rate the difficulty with (U) in the box below. If no: (U) in the box below the reason for not doing so. This may be because of problems relevant to your injury or for reasons not related to your injury. No Strategic level
Not because of my injury
Yes Because of my injury
No difficulty
Slight difficulty
Moderate difficulty
Great difficulty
Slight difficulty
Moderate difficulty
Great difficulty
Slight difficulty
Moderate difficulty
Great difficulty
Driving at dusk Driving for more than 1 hour Driving on a bumpy road No Tactical level
Not because of my injury
Yes Because of my injury
No difficulty
Changing lanes Checking blind spots Driving in bad weather conditions (eg, rain) Driving near (your) accident site Merging on expressways Night driving Reversing No Operational level
Not because of my injury
Yes Because of my injury
No difficulty
Braking suddenly Turning the steering wheel quickly Note: Not because of my injury (not applicable; NA), no difficulty (Score 0), slight difficulty (Score 1), moderate difficulty (Score 2), great difficulty (Score 3), because of my injury (Score 4). Excluding the NA tasks, the score is summed and expressed as a percentage of the total score. A score of 100% indicates the greatest perceived driving difficulty while 0% indicates no perceived driving difficulty.
II. Symptom section During the past 3 months, have you experienced the following symptoms? If yes: rate to what extent the following symptoms have adversely affected your driving ability with (U) in the box below. If no: (U) in the box below. How have they adversely affected your driving? Symptoms Arm pain Difficulty concentrating Dizziness Fatigue Fearfulness Headache Limited neck movement Nausea Neck pain Stress/anxiety Unable to move your head quickly
No
Not at all
Slightly
Moderately
Greatly