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A valid cross-culturally adapted simplified Chinese version of the Quebec Back Pain Disability Scale
Journal of Clinical Epidemiology 65 (2012) 1321e1328
A valid cross-culturally adapted simplified Chinese version of the Quebec Back Pain Disability Scale Xianzhao Weia,1, Honglei Yia,b,1, Bing Wua,c,1, Min Qia,1, Xiangsheng Liua, Zhi Chena, Guoyou Zhanga, Wei Zhangb, Ziqiang Chena, Zongde Yanga, Jiayu Chena, Changwei Yanga, Yushu Baia, Jingfeng Lia, Xiaodong Zhua, Ming Lia,* a
Department of Orthopaedics, Changhai Hospital, Second Military Medical University, No. 168, Changhai Road, Shanghai, 200433, People’s Republic of China b Department of Orthopaedics, 89 Central Hospital of PLA, No. 256, West Beigong Road, Weifang, Shandong, 260122, People’s Republic of China c Department of Orthopaedics, 401 Hospital of PLA, No. 22, Minjiang Road, Qingdao, Shandong, 266071, People’s Republic of China Accepted 5 June 2012; Published online 15 August 2012
Abstract Objective: To evaluate the reliability and validity of the simplified Chinese version of the Quebec Back Pain Disability Scale (SC-QDS). Study Design and Setting: The QDS was translated and cross-culturally adapted into SC following international guidelines. The SC-QDS was completed by 114 patients with low back pain (LBP) and 65 healthy controls, along with the SC Oswestry Disability Index (SC-ODI) and visual analogue scale (VAS). Psychometric evaluation included homogeneity and reproducibility by internal consistency and testeretest reliability and construct validity by calculating the Pearson’s correlation coefficients among QDS, SC-ODI, and VAS. Discriminative validity was determined by student’s t-test. Results: SC-QDS scores were well distributed, with no floor or ceiling effects. Internal consistency was excellent (Cronbach a 0.976). The items and overall SC-QDS were correlated (r 5 0.640e0.898 and P ! 0.0001). Intraclass correlation coefficient of testeretest reliability was excellent (0.987, 95% confidence interval: 0.978e0.992). Construct validity was confirmed by high correlation of SC-QDS and SC-ODI (r 5 0.901 and P ! 0.0001) and VAS (r 5 0.770 and P ! 0.0001) scores, as was discriminative validity by significantly different SC-QDS scores for patients with LBP and controls (46.3 6 19.9 vs. 14.6 6 8.5 and P ! 0.0001). Conclusions: The SC-QDS has good internal consistency, testeretest reliability, and construct and discriminative validity. The SC-QDS is appropriate for clinical and research uses with Chinese-speaking patients with LBP in mainland China. Ó 2012 Elsevier Inc. All rights reserved. Keywords: Reproducibility of results; Culture; Language; Back pain; China; Questionnaires
1. Introduction Low back pain (LBP) is a common cause of disability and has a high recurrence rate. Traditionally, LBP has been most prevalent in industrialized countries [1,2]; however, in recent years the incidence rates have risen worldwide, especially in China [3], possibly because of global urbanization and industrialization and increased awareness [4]. Gaining a detailed understanding of LBP in China may help to develop efficient preventative and treatment strategies. To this
1 Xianzhao Wei, Honglei Yi, Bing Wu, and Min Qi contributed equally to this study. * Corresponding author. Tel.: þ86-21-81873387; fax: þ86-21-81873398. E-mail address: [email protected] (M. Li).
0895-4356/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jclinepi.2012.06.007
end, a standardized assessment method for LBP diagnosis and outcome measures must first be established. Standardized, psychometrically sound, self-report instruments are widely used in clinical settings as outcome measures because of their simplicity, clinical utility, and validity in measuring health status, symptoms, and functional status [5]. Currently, the most widely used instruments for patients with LBP are the Oswestry Disability Index (ODI) [6], the Roland Morris Disability Questionnaire (RMDQ) [7], the Functional Rating Index [8], and the Quebec Back Pain Disability Scale (QDS) [9,10]. Multicenter international research requires cross-culturally adapted and translated assessment instruments and rigorous psychometric testing of the modified instrument in the target population before use [11,12]. A Chinese version of the ODI has been developed [13], but its utility is limited by the
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What is new? The Quebec Disability Scale (QDS) as a functional status questionnaire for low back pain (LBP) was translated into simplified Chinese (SC) and adapted for use in mainland China. Psychometric evaluation of the SC-QDS demonstrated good internal consistency, reproducibility, and construct validity, and discriminative validity. The SC-QDS can be used as a valid instrument for Chinese-speaking patients with LBP in linical practice and research in mainland China.
extensive time required for completion, convoluted phrasing, and culturally awkward items. Thus, a simplified Chinese (SC) questionnaire that is simple to understand, easy to administer, and culturally adapted remains a clinical need. The 20-item QDS [9,10] is widely used in clinical practice and research studies [14e16]. A six-point scale is used for equal-weighted scoring of each item, ranging from 0 (no difficulty at all to function) to 5 (unable to perform this function). The summed total score indicates disability extent, ranging from 0 (no disability) to 100 (maximal disability). The QDS has been successfully adapted for measuring LBP impairment in several different cultural and language groups, including Dutch [17], French [18], Iranian [19], Brazilian [20], Turkish [21,22], Polish [23], and Korean [24]. However, no validated SC-QDS version has been reported. Therefore, we translated and culturally adapted the QDS into SC and investigated its reliability and validity when administered to 114 Chinese-speaking patients with LBP in mainland China.
2. Materials and methods 2.1. Translation and cross-cultural adaptation The translation and cross-cultural adaptation of the QDS English version to SC was performed according to international guidelines [11,12]. Two bilingual translators, who spoke Chinese as a first language, independently performed the forward translation to SC. One translator was the author of this article (Xianzhao Wei), who was aware of the translation purpose and the concepts underlying the QDS. The other translator was an English teacher with no medical background and was blinded to the study’s purpose. An expert committee was formed, composed of two translators, two orthopedic surgeons, one physician of rehabilitation, one physical therapist, and two patients with LBP to compare the translations with each other and with the original English version; afterward, the two forward translations
were amalgamated. The few remaining discrepancies were resolved by consensus. The backward translation was performed by two independent native English speakers with Chinese as their second language, who were blinded to the study purpose. Both translators lacked medical background and were unaware of the prior translation procedures or the original document. Each English translation was compared with the original English QDS and checked for inconsistencies by the expert committee. The expert committee consolidated the original questionnaire, translations, back translations, and corresponding written reports to reach a consensus. The committee also reached agreement on the semantic, idiomatic, experiential, and conceptual equivalence between the original and the target versions. Finally, the prefinal SC-QDS was pilot tested in 35 patients with LBP. Each patient completed the SC-QDS and was subsequently interviewed about any difficulties in completing the questionnaire or understanding the purpose and meaning of each question. The expert committee discussed all the findings and then developed the final SC-QDS (Appendix), which was subjected to further psychometric testing. 2.2. Participants One hundred and fourteen patients with a diagnosis of nonspecific LBP were recruited from the outpatient orthopedic department of a major hospital in a large metropolitan city in mainland China between January and June 2011. The patient population number was based on the Quality criteria for health status questionnaires [25], which advised that 100 patients are necessary for internal consistency analysis and 50 for appropriate analyses of reliability, construct validity, and ceiling or floor effects. The inclusion criteria were as follows: age O18 years, ability to read and speak Chinese, and LBP 6 weeks. Exclusion criteria included the following: history of spinal surgery, tumors, infection, systemic rheumatologic disease, ankylosing spondylitis, or neurologic disorders and inability or unwillingness to complete questionnaires independently. Demographic and clinical characteristics of all participants were recorded. Sixty-five age-matched pain-free individuals without LBP or history of LBP were recruited as controls. The controls provided their medical history and underwent a physical examination before voluntary enrollment. None of the controls had current or previous problems with their lumbar or lower limbs. The project was approved by the Human Research Ethics Committee of the Second Military Medical University, and each patient provided written informed consent. 2.3. Acceptability The time required to answer the SC-QDS was recorded, and the patients were queried about any difficulties encountered during the process. The quality of data was measured by the amount of missing or multiple responses.
X. Wei et al. / Journal of Clinical Epidemiology 65 (2012) 1321e1328
2.4. Score distribution Floor and ceiling effects (defined as the percentage of participants displaying the minimum and maximum possible scores, respectively) were described and those O15% were considered significant [25]. 2.5. Reliability 2.5.1. Homogeneity Internal consistency was used to evaluate SC-QDS homogeneity. Cronbach a for the overall SC-QDS and Cronbach a if an item was deleted were calculated to assess the internal consistency coefficient. High Cronbach a indicates high correlations among items. In addition, the correlations of each item with the overall SC-QDS were calculated. Good internal consistency and high correlation between each item and the overall questionnaire ensure that all the items in the questionnaire measure the same construct. 2.5.2. Reproducibility To assess the reproducibility of the SC-QDS, 60 patients were randomly selected by a computer-generated randomized table to recomplete the questionnaire booklet. The time interval was designed to be 7 days. Two-way ANOVA random-effects intraclass correlation coefficient (ICC) was calculated to quantify the testeretest reliability. Withinsubject variation and limits of agreement were assessed by the BlandeAltman plot [26]. 2.6. Validity Construct validity was assessed by calculating the Pearson’s correlation coefficients among SC-QDS, SC-ODI, and visual analogue scale (VAS) scores. ODI is a widely used and validated instrument to evaluate the functional status of LBP, and a validated SC-ODI version exists [13]. It comprises 10 sections that are scored from 0 to 5. Doubling the sum of the section scores gives the total score, which is reported as a percentage of the patient’s perceived disability. The VAS allows patients to rate their current pain intensity along a 100-mm line with ‘‘no pain’’ at the far left and ‘‘worst pain’’ at the far right. All 114 patients completed the three Chinese language questionnaires. Discriminative validity was assessed by administering the SC-QDS only to 65 healthy pain-free subjects. The SC-QDS scores between pain-free individuals and patients with LBP selected in the retest section were compared using an independent t-test. The SC-QDS scores of patients with LBP were expected to be significantly higher than those of pain-free individuals. 2.7. Statistical analysis Data analysis was performed with SPSS 18.0 (SPSS, Chicago, IL, USA). Mean values are reported with standard deviations. Cronbach a of 0.70 was considered
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satisfactory [27]. ICC values are reported with 95% confidence intervals (CIs). An ICC value between 0.60 and 0.80 indicated good reliability and values O0.80 indicated excellent reliability [28]. Correlation values were as follows: poor: r 5 0e0.20; fair: r 5 0.21e0.40; moderate: r 5 0.41e0.60; very good: r 5 0.61e0.80; or excellent: r 5 0.81e1.0 [8]. P-values !0.05 indicated statistical significance. 3. Results 3.1. Cross-cultural adaptation For ease of understanding and cultural relevance, we modified some QDS items. The 16th item ‘‘Bend over to clean the bathtub’’ was modified to ‘‘Bend over to do some washing,’’ in accordance with the fact that a bathtub is not frequently used by Chinese people but bending over for washing is. In addition, the distance measure ‘‘block’’ is unfamiliar in China, so we defined one ‘‘block’’ as ‘‘100 meters,’’ as suggested by the authors of the original QDS. 3.2. Patient characteristics Table 1 summarizes the demographic and clinical characteristics of the test and retest patients with LBP and healthy pain-free subjects. 3.3. Acceptability All patients completed the SC-QDS with no difficulty. On average, it took 2.4 6 0.5 minutes. The completion rate was 92%, and occurrences of missing or multiple responses were rare. The response rate for section 8 of the ODI (sexual activity) was remarkably lower (73%) than that of other sections, which agreed with previously reported findings
Table 1. Demographic characteristics and the score distribution of the study population
Variables Subjects, n Sex, n (%) Female Male Age (y, mean 6 SD) Pain duration (wk, mean 6 SD) Schober (cm, mean 6 SD) VAS (mm, mean 6 SD) SC-ODI (mean 6 SD) SC-QDS (mean 6 SD) Floor effects (%) Ceiling effects (%)
Patient group (test)
Patient subgroup (retest)
Pain-free group
114
60
65
64 (56.1%) 22 (36.7%) 30 (46.2%) 50 (43.9%) 38 (63.3%) 35 (53.8%) 49.9 6 9.2 49.6 6 9.3 50.1 6 8.7 18.3 6 6.4 19.5 6 7.1 d 4.52 6 0.81 d d 60.0 6 20.6 61.1 6 19.9 d 35.7 6 15.4 36.2 6 14.2 d 44.2 6 18.9 46.3 6 19.9 14.6 6 8.5 0 0 d 0 0 d
Abbreviations: SC, simplified Chinese; QDS, Quebec Back Pain Disability Scale; ODI, Oswestry Disability Index; SD, standard deviation.
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[13,29]. Thus, the SC-QDS was simple and quick for a Chinese-speaking population with LBP.
QDS score of the patients with LBP was significantly higher than that of the pain-free group (46.3 6 19.9 vs. 14.6 6 8.5 and P ! 0.0001) (Table 1).
3.4. Score distribution The distribution of scores for SC-QDS, VAS, and SCODI are shown in Table 1. The SC-QDS scores were well distributed with no floor or ceiling effects. Fig. 1 illustrates the frequency histogram of SC-QDS scores for the test group. 3.5. Reliability 3.5.1. Homogeneity The Cronbach a was 0.976 for the overall SC-QDS. Cronbach a ranged from 0.974 to 0.977 if an item was deleted, indicating excellent internal consistency. The itemetotal score correlations were significant (P ! 0.001) with Pearson’s coefficients ranging from 0.640 (item 16) to 0.898 (item 19). The detailed results of the itemetotal correlations and Cronbach a if an item was deleted are shown in Table 2. Our data showed that the SC-QDS items have good homogeneity. 3.5.2. Reproducibility The average interval between test and retest was 7.2 days (range: 5e8 days). The ICC of testeretest reliability was excellent and reached 0.987 (95% CI 0.978e0.992). The BlandeAltman plot (Fig. 2) shows the differences between measures from the two test sessions against the mean of the two sessions for each patient. The limits of agreement ranged from 9.0 to 8.8. No systematic bias between test and retest SC-QDS total scores was found, indicating good testeretest agreement. 3.6. Validity 3.6.1. Discriminative validity The SC-QDS scores between the randomly selected 60 patients in the retest group and the 65 pain-free individuals were significantly different. As expected, the mean SC-
Fig. 1. Distribution of the SC-QDS score (test group, n 5 114).
3.6.2. Construct validity The associations between SC-QDS and VAS or SC-ODI are presented in Table 3. Construct validity assessed by Pearson’s correlation coefficients between SC-QDS and SC-ODI or VAS indicated that the SC-QDS was significantly correlated with the SC-ODI (r 5 0.901 and P ! 0.0001) and VAS (r 5 0.770 and P ! 0.0001) in the test section (n 5 114). Thus, the SC-QDS had good construct validity.
4. Discussion The QDS is a back-specific, self-report outcome measure for patients with LBP, which contains 20 items in six domains (bed/rest, sitting or standing, ambulation, movement, bending/stooping, and handling large or heavy objects) to assess functional ability in daily life [9,10]. The original QDS is proven to have satisfactory psychometric properties [9,10]. When a questionnaire is considered for use in a new country, culture, or language, it must not only be well translated linguistically and appropriately adapted culturally but must maintain the original psychometric properties of the source version [30]. The QDS has been cross-culturally adapted into several different versions, with its related psychometric properties being successfully maintained (summarized in Table 4). In recent years, Chinese spinal surgeons, physicians, and other health care professionals have given more attention to heath-related quality-of-life issues that may impact their patients. As a result, the need for a method to accurately assess the Chinese-speaking patients’ perspective of the impact of LBP has risen. This study aimed to develop a simplified Chinese QDS and validate it for patients with LBP in mainland China. Psychometric testing of the resultant SC-QDS demonstrated its reliability and validity in measuring the functional status of Chinese-speaking patients with LBP. In particular, the score distribution of SC-QDS was satisfactory and there were no floor or ceiling effects. No patients experienced difficulty completing the questionnaires. Moreover, the SC-QDS had a 92% overall completion rate, whereas section 8 of the SC-ODI (sexual activity) had a low response rate. This low response rate may reflect the very private nature of sexual activity in the Chinese culture. Such missing responses can result in inaccurate assessments. Our results showed that the SC-QDS was simple to use, quickly self-completed, and had good clinical utility. According to previous reports, all different language versions of QDS possess good internal consistency with high Cronbach a range (0.92e0.96) [9,17,19e24]. The
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Table 2. Itemetotal score correlations of each item and Cronbach a if an item was deleted from the SC-QDS Itemetotal score correlation SC-QDS item Get out of bed Sleep through the night Turn over in bed Ride in a car Stand up for 20e30 min Sit in a chair for several hours Climb one flight of stairs Walk a few blocks (300e400 m) Walk several kilometers Reach up to high shelves Throw a ball Run one block (about 100 m) Take food out of the refrigerator Make your bed Put on socks (pantyhose) Bend over to clean the bathtub Move a chair Pull or push heavy doors Carry two bags of groceries Lift and carry a heavy suitcase
r
P-value
Cronbach a if an was item deleted
0.751 0.856 0.849 0.885 0.879 0.860 0.847 0.863 0.865 0.869 0.837 0.725 0.810 0.777 0.846 0.640 0.854 0.882 0.898 0.828
!0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001
0.976 0.975 0.975 0.974 0.975 0.975 0.975 0.975 0.975 0.975 0.975 0.976 0.975 0.976 0.975 0.977 0.975 0.974 0.974 0.975
SC-QDS internal consistency was excellent, with the Cronbach a reaching 0.976, higher than that of all other versions: original (0.96) [9], Dutch (0.95) [17], Iranian (0.92) [19], Brazilian (0.97) [20], Turkish (test, 0.941 and retest, 0.957) [21,22], Polish (0.95) [23], and Korean (0.92) [24]. It was noteworthy that the SC-QDS Cronbach a was limited to a very small range (0.974e0.976) if an item was deleted. The itemetotal score correlations were used to quantitate the strength of correlation between each item and the total scores [31]. Moreover, each item was significantly correlated to the overall questionnaire (Pearson’s coefficients ranging from 0.640 [item 16] to 0.898 [item 19]), indicating that each item assessed the same aspect
of the construct. The itemetotal correlations of SC-QDS were higher than those of the original [9], Dutch [17], French [18], and Turkish [22] versions. To evaluate testeretest reliability, it is generally suggested that the time period between repeated administrations should be long enough to prevent recall but short enough to ensure that clinical change has not occurred. No definitive time interval has been experimentally determined, and 1 or 2 weeks are often considered to be appropriate [25]. The time intervals used for the reliability test in other studies were 3e4 days (Brazilian) [20], 1 day (Iranian and Turkish) [19,22], 2 days (Polish) [23], 1e14 days with an average of 3.8 days (original study) [9], 1 week (Dutch)
Fig. 2. BlandeAltman plot for testeretest agreement of the SC-QDS. The differences between patients for the measures from the two test sessions were plotted against the mean of the two sessions for the SC-QDS total scores. The dashed line indicates the 95% (61.96 standard deviation) limits of agreement.
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Table 3. Pearson’s correlations between SC-QDS and SC-ODI/VAS in the test group (n 5 114)
correlation between the scores of SC-QDS and SC-ODI; the Pearson’s correlation coefficient was 0.870 (P ! 0.0001), similar to that of the Polish version (r 5 0.841 in test and r 5 0.866 in retest) [23] but higher than that of the original English (r 5 0.77) [9], the Iranian (r 5 0.76) [19], the Turkish (r 5 0.67 in test and r 5 0.68 in retest) [22], and the Korean versions (r 5 0.718 in test and r 5 0.690 in retest) [24]. Previous studies indicated that QDS is significantly correlated to patients’ pain severity, with the Pearson’s correlation coefficient between QDS and VAS ranging from 0.37 to 0.75 [18,20e22,24]. The variation in results from previous studies is not surprising given the multidimensional complexity of pain, especially in chronic form. Our study demonstrated that SC-QDS and VAS are significantly correlated; the test (r 5 0.770) and retest (r 5 0.754) were even higher than those previously reported. In addition, the high correlation between the SC-QDS and the SC-ODI/VAS indicated good construct validity for the SC-QDS. In other published studies that evaluated the different versions of QDS, the patient population size ranged from 32 [18] to 130 [20] (Table 4). Our study included 114 patients coming from different areas of mainland China; however, there may still be some potential patient selection bias. Although the number of patients in our study was relatively small, it was sufficient by statistical analysis requirements. Our study only included patients with LBP O6 weeks, and none of the patients had received surgery. The patient population included in this study was similar to those used in other studies [17e24], which might represent a common limitation shared among these studies. Considering the exceedingly large population in China, we believe that an SC-QDS study using a larger population in mainland China is still needed. Responsiveness, defined as the ability to detect clinically important changes over time, is a critical property of medical questionnaires [25]. The study by Demoulin et al. [32] demonstrated that QDS was responsive and showed
SC-QDS Test score VAS SC-ODI
r
95% CI
P-value
0.870 0.901
0.796e0.923 0.867e0.934
!0.0001 !0.0001
Abbreviation: VAS, visual analogue scale.
[17], and 2 weeks (Korean) [24]. In our study, 60 patients were randomly selected to complete the SC-QDS questionnaire twice and the time interval for the recompletion of SC-QDS was 1 week. The reasoning for this time included the belief that a 1-week interval ensured that patients who received medical treatment would not have experienced an obvious clinical change and the fact that 1 week is the time that patients are required to wait for surgery, thereby ensuring that patients arranged for surgery would not be omitted from the reliability evaluation. For the analysis of SC-QDS testeretest reliability, the high value of ICC (0.987) revealed an excellent reproducibility. Comparison with other versions showed that the SC-QDS ICC was higher than that of the original (0.92) [9], Dutch (0.90) [17], Iranian (0.86) [19], Brazilian (0.93) [20], Turkish (0.92) [22], Polish (0.93) [23], and Korean (0.91) [24] versions. To our knowledge, no previous study has tested the psychometric property of discriminative ability for the different QDS versions [9,17e24]. However, the SC-QDS was tested and found to have discriminative validity (divergent construct validity), as evidenced by higher scores for patients with LBP than for pain-free controls. ODI and RMDQ are two of the most frequently applied instruments to evaluate QDS construct validity. Previous studies showed that QDS is significantly correlated to RMDQ (Pearson’s correlation coefficient range: 0.60e0.91) [9,17,19,20]. In our study, SC-ODI was selected as the comparison measure to evaluate the construct and concurrent validity of the SC-QDS. We found a significant and strong
Table 4. Summary of evidence on reliability and validity of various versions of the QDS for LBP Reliability Testeretest QDS versions English (Canada) [9], 1995 French (Canada) [9], 1995 French (France) [18], 2002 Iranian [19], 2006 Brazilian [20], 2009 Turkish [21], 2005 Turkish [22], 2009
Validity
Internal consistency
n
ICC
n
Cronbach a
n
Tested variable
Pearson’s correlation,r
52 46 d 31 54 d 100
0.93 0.88 d 0.86 0.93 d 0.92
123 102 d 100 54 83 100
0.95 0.96 d 0.92 0.97 0.93 0.94 (test)
130 112 32 100 54 83 100
ODI ODI VAS ODI VAS VAS VAS
0.77 0.83 0.45 0.76 0.75 0.46 0.37 (test) 0.44 (retest) 0.67 (test) 0.68 (retest) 0.84 (test) 0.87 (retest) 0.718 0.647
0.96 (retest) Polish [23], 2011
85
0.93
111
Korean [24], 2011
59
0.91
80
0.95 (test) 0.95 (retest) 0.92
Abbreviations: n, Sample size; ICC, intraclass correlation coefficient.
ODI 111
ODI
80
ODI VAS
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reasonable interpretability after a multidisciplinary treatment. Wilhelm et al. [33] showed that, in a sample of chronic LBP sufferers, the QDS was more sensitive to clinical change than was the Dallas Pain Questionnaire. It was recommended that for the QDS, a 30% change (20 points) from baseline may be considered as clinically meaningful improvement when comparing before and after measures for individual patients [34]. However, in this study, we did not report the responsiveness of SC-QDS because of the short time follow-up and lack of head-to-head comparative data. Other published studies (involving the Turkish, Brazilian, French, Korean, Polish, Iranian, and Dutch versions) similarly did not report the responsiveness of QDS, which is a shared shortcoming. Comparative study of SC-QDS responsiveness with other instruments, such as SC-ODI and SC-RMDQ, is under way by our group. 5. Conclusions The English QDS was successfully translated into SC and culturally adapted for use in mainland China. The SC-QDS is easy to understand and quick to complete. The psychometric properties of the original version are maintained. The SC-QDS has good homogeneity, reproducibility, and discriminative and construct validity. We suggest that the SC-QDS can be widely used for assessing function in patients with LBP in mainland China. Acknowledgments No grants or technical or financial support were used for this study. So none needs to be acknowledged. No conflicts of interest exist for any of the study’s authors. Appendix supplementary data Supplementary data related to this article can be found online at http://dx.doi.org/10.1016/j.jclinepi.2012.06.007. References [1] Shelerud RA. Epidemiology of occupational low back pain. Clin Occup Environ Med 2006;5:501e28. [v]. [2] Merkesdal S, Mau W. Prediction of costs-of-illness in patients with low back pain undergoing orthopedic outpatient rehabilitation. Int J Rehabil Res 2005;28:119e26. [3] Jin K, Sorock GS, Courtney T, Liang Y, Yao Z, Matz S, et al. Risk factors for work-related low back pain in the People’s Republic of China. Int J Occup Environ Health 2000;6:26e33. [4] Barrero LH, Hsu YH, Terwedow H, Perry MJ, Dennerlein JT, Brain JD, et al. Prevalence and physical determinants of low back pain in a rural Chinese population. Spine 2006;31:2728e34. [5] Costa LO, Maher CG, Latimer J. Self-report outcome measures for low back pain: searching for international cross-cultural adaptations. Spine 2007;32:1028e37.
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[6] Fairbank JC, Pynsent PB. The Oswestry Disability Index. Spine 2000;25:2940e52. [7] Roland M, Morris R. A study of the natural history of back pain: I. Development of a reliable and sensitive measure of disability of low back pain. Spine 1983;8:141e4. [8] Feise JF, Menke M. Functional Rating Index: a new valid and reliable instrument to measure the magnitude of clinical change in spinal conditions. Spine 2001;26:78e87. [9] Kopec JA, Esdaile JM, Abrahamowicz M, Abenhaim L, WoodDauphinee S, Lamping DL, et al. The Quebec Back Pain Disability Scale. Measurement properties. Spine 1995;20:341e52. [10] Kopec KA, Esdaile JM, Abrahamowicz M. The Quebec Back Pain Disability Scale: conceptualization and development. J Clin Epidemiol 1996;49:151e61. [11] Guillemin F, Bombardier C, Beaton D. Cross-cultural adaptation of health-related quality of life measures: literature review and proposed guidelines. J Clin Epidemiol 1993;46:1417e32. [12] Beaton DE, Bombardier C, Guillemin F, Ferraz MB. Guidelines for the process of cross-cultural adaptation of self-report measures. Spine 2000;25:3186e91. [13] Liu H, Tao H, Luo Z. Validation of the simplified Chinese version of the Oswestry Disability Index. Spine 2009;34:1211e6. [discussion 1217]. [14] Conway J, Tomkins CC, Haig AJ. Walking assessment in people with lumbar spinal stenosis: capacity, performance, and self-report measures. Spine J 2011;11:816e23. [15] Morgalla MH, Noak N, Merkle M, Tatagiba MS. Lumbar spinal stenosis in elderly patients: is a unilateral microsurgical approach sufficient for decompression? J Neurosurg Spine 2011;14:305e12. [16] Smeets R, K€oke A, Lin CW, Ferreira M, Demoulin C. Measures of function in low back pain/disorders: Low Back Pain Rating Scale (LBPRS), Oswestry Disability Index (ODI), Progressive Isoinertial Lifting Evaluation (PILE), Quebec Back Pain Disability Scale (QBPDS), and Roland-Morris Disability Questionnaire (RDQ). Arthritis Care Res 2011;63:S158e73. [17] Schoppink LE, van Tulder MW, Koes BW, Beurskens SA, de Bie RA. Reliability and validity of the Dutch adaptation of the Quebec Back Pain Disability Scale. Phys Ther 1996;76:268e75. [18] Yvanes-Thomas M, Calmels P, Bethoux F, Richard A, Nayme P, Payre D, et al. Validity of the French language version of the Quebec back pain disability scale in low back pain patients in France. Joint Bone Spine 2002;69:397e405. [19] Mousavi SJ, Parnianpour M, Mehdian H, Montazeri A, Mobini B. The Oswestry Disability Index, the Roland Morris Disability Questionnaire, and the Quebec Back Pain Disability Scale: translation and validation studies of the Iranian versions. Spine 2006;31:E454e9. [20] Rodrigues MF, Michel-Crosato E, Cardoso JR, Traebert J. Psychometric properties and cross-cultural adaptation of the Brazilian Quebec back pain disability scale questionnaire. Spine 2009;34:E459e64. [21] Bicer A, Yazici A, Camdeviren H, Milcan A, Erdogan C. Assessment of pain and disability in patients with chronic low back pain: reliability and construct validity of the Turkish version of the Quebec Back Pain Disability Scale and Pain Disability Index. J Back Musculoskeletal Rehabil 2005;18:37e44. [22] Melikoglu MA, Kocabas H, Sezer I, Bilgilisoy M, Tuncer T. Validation of the Turkish version of the Quebec back pain disability scale for patients with low back pain. Spine 2009;34:E219e24. [23] Misterska E, Jankowski R, Glowacki M. Quebec Back Pain Disability Scale, Low Back Outcome Score and Revised Oswestry Low Back Pain Disability Scale for patients with low back pain due to degenerative disc disease: evaluation of Polish versions. Spine 2011;36:E1722e9. [24] Suh KT, Kim JI, Lim JM, Goh TS, Lee JS. Validation of the Korean Version of the Quebec Back Pain Disability Scale. J Spinal Disord Tech 2011. [Epub ahead of print]. [25] Terwee CB, Bot SD, de Boer MR, van der Windt DA, Knol DL, Dekker J, et al. Quality criteria were proposed for measurement properties of health status questionnaires. J Clin Epidemiol 2007;60:34e42.
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[26] Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986; 1:307e10. [27] Cronbach LJ. Coefficient alpha and the internal structure of tests. Psychometrika 1951;16:297e334. [28] Shrout PE, Fleiss J. Intraclass correlations: uses in assessing rater reliability. Psychol Bull 1979;86:420e8. [29] Wei X, Chen Z, Bai Y, et al. Validation of the Simplified Chinese Version of the Functional Rating Index (FRI) for patients with low back pain. Spine 2012;37:1602e8. [30] Bullinger M, Alonso J, Apolone G, Leplege A, Sullivan M, WoodDauphinee S, et al. Translating health status questionnaires and evaluating their quality: the IQOLA Project approach. International Quality of Life Assessment. J Clin Epidemiol 1998;51:913e23.
[31] Fermanian J. Evaluating correctly the validity of a rating scale: the numerous pitfalls to avoid. Rev Epidemiol Sante Publique 1996;44:278e86. [32] Demoulin C, Ostelo R, Knottnerus JA, Smeets RJ. Quebec Back Pain Disability Scale was responsive and showed reasonable interpretability after a multidisciplinary treatment. J Clin Epidemiol 2010;63:1249e55. [33] Wilhelm F, Fayolle-Minon I, Phaner V, Le-Quang B, Rimaud D, Bethoux F, et al. Sensitivity to change of the Quebec Back Pain Disability Scale and the Dallas Pain Questionnaire. Ann Phys Rehabil Med 2010;53:15e23. [34] Ostelo RW, Deyo RA, Stratford P, Waddell G, Croft P, Von Korff M, et al. Interpreting change scores for pain and functional status in low back pain: towards international consensus regarding minimal important change. Spine 2008;33:90e4.
A valid cross-culturally adapted simplified Chinese version of the Quebec Back Pain Disability Scale Xianzhao Weia,1, Honglei Yia,b,1, Bing Wua,c,1, Min Qia,1, Xiangsheng Liua, Zhi Chena, Guoyou Zhanga, Wei Zhangb, Ziqiang Chena, Zongde Yanga, Jiayu Chena, Changwei Yanga, Yushu Baia, Jingfeng Lia, Xiaodong Zhua, Ming Lia,* a
Department of Orthopaedics, Changhai Hospital, Second Military Medical University, No. 168, Changhai Road, Shanghai, 200433, People’s Republic of China b Department of Orthopaedics, 89 Central Hospital of PLA, No. 256, West Beigong Road, Weifang, Shandong, 260122, People’s Republic of China c Department of Orthopaedics, 401 Hospital of PLA, No. 22, Minjiang Road, Qingdao, Shandong, 266071, People’s Republic of China Accepted 5 June 2012; Published online 15 August 2012
Abstract Objective: To evaluate the reliability and validity of the simplified Chinese version of the Quebec Back Pain Disability Scale (SC-QDS). Study Design and Setting: The QDS was translated and cross-culturally adapted into SC following international guidelines. The SC-QDS was completed by 114 patients with low back pain (LBP) and 65 healthy controls, along with the SC Oswestry Disability Index (SC-ODI) and visual analogue scale (VAS). Psychometric evaluation included homogeneity and reproducibility by internal consistency and testeretest reliability and construct validity by calculating the Pearson’s correlation coefficients among QDS, SC-ODI, and VAS. Discriminative validity was determined by student’s t-test. Results: SC-QDS scores were well distributed, with no floor or ceiling effects. Internal consistency was excellent (Cronbach a 0.976). The items and overall SC-QDS were correlated (r 5 0.640e0.898 and P ! 0.0001). Intraclass correlation coefficient of testeretest reliability was excellent (0.987, 95% confidence interval: 0.978e0.992). Construct validity was confirmed by high correlation of SC-QDS and SC-ODI (r 5 0.901 and P ! 0.0001) and VAS (r 5 0.770 and P ! 0.0001) scores, as was discriminative validity by significantly different SC-QDS scores for patients with LBP and controls (46.3 6 19.9 vs. 14.6 6 8.5 and P ! 0.0001). Conclusions: The SC-QDS has good internal consistency, testeretest reliability, and construct and discriminative validity. The SC-QDS is appropriate for clinical and research uses with Chinese-speaking patients with LBP in mainland China. Ó 2012 Elsevier Inc. All rights reserved. Keywords: Reproducibility of results; Culture; Language; Back pain; China; Questionnaires
1. Introduction Low back pain (LBP) is a common cause of disability and has a high recurrence rate. Traditionally, LBP has been most prevalent in industrialized countries [1,2]; however, in recent years the incidence rates have risen worldwide, especially in China [3], possibly because of global urbanization and industrialization and increased awareness [4]. Gaining a detailed understanding of LBP in China may help to develop efficient preventative and treatment strategies. To this
1 Xianzhao Wei, Honglei Yi, Bing Wu, and Min Qi contributed equally to this study. * Corresponding author. Tel.: þ86-21-81873387; fax: þ86-21-81873398. E-mail address: [email protected] (M. Li).
0895-4356/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jclinepi.2012.06.007
end, a standardized assessment method for LBP diagnosis and outcome measures must first be established. Standardized, psychometrically sound, self-report instruments are widely used in clinical settings as outcome measures because of their simplicity, clinical utility, and validity in measuring health status, symptoms, and functional status [5]. Currently, the most widely used instruments for patients with LBP are the Oswestry Disability Index (ODI) [6], the Roland Morris Disability Questionnaire (RMDQ) [7], the Functional Rating Index [8], and the Quebec Back Pain Disability Scale (QDS) [9,10]. Multicenter international research requires cross-culturally adapted and translated assessment instruments and rigorous psychometric testing of the modified instrument in the target population before use [11,12]. A Chinese version of the ODI has been developed [13], but its utility is limited by the
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What is new? The Quebec Disability Scale (QDS) as a functional status questionnaire for low back pain (LBP) was translated into simplified Chinese (SC) and adapted for use in mainland China. Psychometric evaluation of the SC-QDS demonstrated good internal consistency, reproducibility, and construct validity, and discriminative validity. The SC-QDS can be used as a valid instrument for Chinese-speaking patients with LBP in linical practice and research in mainland China.
extensive time required for completion, convoluted phrasing, and culturally awkward items. Thus, a simplified Chinese (SC) questionnaire that is simple to understand, easy to administer, and culturally adapted remains a clinical need. The 20-item QDS [9,10] is widely used in clinical practice and research studies [14e16]. A six-point scale is used for equal-weighted scoring of each item, ranging from 0 (no difficulty at all to function) to 5 (unable to perform this function). The summed total score indicates disability extent, ranging from 0 (no disability) to 100 (maximal disability). The QDS has been successfully adapted for measuring LBP impairment in several different cultural and language groups, including Dutch [17], French [18], Iranian [19], Brazilian [20], Turkish [21,22], Polish [23], and Korean [24]. However, no validated SC-QDS version has been reported. Therefore, we translated and culturally adapted the QDS into SC and investigated its reliability and validity when administered to 114 Chinese-speaking patients with LBP in mainland China.
2. Materials and methods 2.1. Translation and cross-cultural adaptation The translation and cross-cultural adaptation of the QDS English version to SC was performed according to international guidelines [11,12]. Two bilingual translators, who spoke Chinese as a first language, independently performed the forward translation to SC. One translator was the author of this article (Xianzhao Wei), who was aware of the translation purpose and the concepts underlying the QDS. The other translator was an English teacher with no medical background and was blinded to the study’s purpose. An expert committee was formed, composed of two translators, two orthopedic surgeons, one physician of rehabilitation, one physical therapist, and two patients with LBP to compare the translations with each other and with the original English version; afterward, the two forward translations
were amalgamated. The few remaining discrepancies were resolved by consensus. The backward translation was performed by two independent native English speakers with Chinese as their second language, who were blinded to the study purpose. Both translators lacked medical background and were unaware of the prior translation procedures or the original document. Each English translation was compared with the original English QDS and checked for inconsistencies by the expert committee. The expert committee consolidated the original questionnaire, translations, back translations, and corresponding written reports to reach a consensus. The committee also reached agreement on the semantic, idiomatic, experiential, and conceptual equivalence between the original and the target versions. Finally, the prefinal SC-QDS was pilot tested in 35 patients with LBP. Each patient completed the SC-QDS and was subsequently interviewed about any difficulties in completing the questionnaire or understanding the purpose and meaning of each question. The expert committee discussed all the findings and then developed the final SC-QDS (Appendix), which was subjected to further psychometric testing. 2.2. Participants One hundred and fourteen patients with a diagnosis of nonspecific LBP were recruited from the outpatient orthopedic department of a major hospital in a large metropolitan city in mainland China between January and June 2011. The patient population number was based on the Quality criteria for health status questionnaires [25], which advised that 100 patients are necessary for internal consistency analysis and 50 for appropriate analyses of reliability, construct validity, and ceiling or floor effects. The inclusion criteria were as follows: age O18 years, ability to read and speak Chinese, and LBP 6 weeks. Exclusion criteria included the following: history of spinal surgery, tumors, infection, systemic rheumatologic disease, ankylosing spondylitis, or neurologic disorders and inability or unwillingness to complete questionnaires independently. Demographic and clinical characteristics of all participants were recorded. Sixty-five age-matched pain-free individuals without LBP or history of LBP were recruited as controls. The controls provided their medical history and underwent a physical examination before voluntary enrollment. None of the controls had current or previous problems with their lumbar or lower limbs. The project was approved by the Human Research Ethics Committee of the Second Military Medical University, and each patient provided written informed consent. 2.3. Acceptability The time required to answer the SC-QDS was recorded, and the patients were queried about any difficulties encountered during the process. The quality of data was measured by the amount of missing or multiple responses.
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2.4. Score distribution Floor and ceiling effects (defined as the percentage of participants displaying the minimum and maximum possible scores, respectively) were described and those O15% were considered significant [25]. 2.5. Reliability 2.5.1. Homogeneity Internal consistency was used to evaluate SC-QDS homogeneity. Cronbach a for the overall SC-QDS and Cronbach a if an item was deleted were calculated to assess the internal consistency coefficient. High Cronbach a indicates high correlations among items. In addition, the correlations of each item with the overall SC-QDS were calculated. Good internal consistency and high correlation between each item and the overall questionnaire ensure that all the items in the questionnaire measure the same construct. 2.5.2. Reproducibility To assess the reproducibility of the SC-QDS, 60 patients were randomly selected by a computer-generated randomized table to recomplete the questionnaire booklet. The time interval was designed to be 7 days. Two-way ANOVA random-effects intraclass correlation coefficient (ICC) was calculated to quantify the testeretest reliability. Withinsubject variation and limits of agreement were assessed by the BlandeAltman plot [26]. 2.6. Validity Construct validity was assessed by calculating the Pearson’s correlation coefficients among SC-QDS, SC-ODI, and visual analogue scale (VAS) scores. ODI is a widely used and validated instrument to evaluate the functional status of LBP, and a validated SC-ODI version exists [13]. It comprises 10 sections that are scored from 0 to 5. Doubling the sum of the section scores gives the total score, which is reported as a percentage of the patient’s perceived disability. The VAS allows patients to rate their current pain intensity along a 100-mm line with ‘‘no pain’’ at the far left and ‘‘worst pain’’ at the far right. All 114 patients completed the three Chinese language questionnaires. Discriminative validity was assessed by administering the SC-QDS only to 65 healthy pain-free subjects. The SC-QDS scores between pain-free individuals and patients with LBP selected in the retest section were compared using an independent t-test. The SC-QDS scores of patients with LBP were expected to be significantly higher than those of pain-free individuals. 2.7. Statistical analysis Data analysis was performed with SPSS 18.0 (SPSS, Chicago, IL, USA). Mean values are reported with standard deviations. Cronbach a of 0.70 was considered
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satisfactory [27]. ICC values are reported with 95% confidence intervals (CIs). An ICC value between 0.60 and 0.80 indicated good reliability and values O0.80 indicated excellent reliability [28]. Correlation values were as follows: poor: r 5 0e0.20; fair: r 5 0.21e0.40; moderate: r 5 0.41e0.60; very good: r 5 0.61e0.80; or excellent: r 5 0.81e1.0 [8]. P-values !0.05 indicated statistical significance. 3. Results 3.1. Cross-cultural adaptation For ease of understanding and cultural relevance, we modified some QDS items. The 16th item ‘‘Bend over to clean the bathtub’’ was modified to ‘‘Bend over to do some washing,’’ in accordance with the fact that a bathtub is not frequently used by Chinese people but bending over for washing is. In addition, the distance measure ‘‘block’’ is unfamiliar in China, so we defined one ‘‘block’’ as ‘‘100 meters,’’ as suggested by the authors of the original QDS. 3.2. Patient characteristics Table 1 summarizes the demographic and clinical characteristics of the test and retest patients with LBP and healthy pain-free subjects. 3.3. Acceptability All patients completed the SC-QDS with no difficulty. On average, it took 2.4 6 0.5 minutes. The completion rate was 92%, and occurrences of missing or multiple responses were rare. The response rate for section 8 of the ODI (sexual activity) was remarkably lower (73%) than that of other sections, which agreed with previously reported findings
Table 1. Demographic characteristics and the score distribution of the study population
Variables Subjects, n Sex, n (%) Female Male Age (y, mean 6 SD) Pain duration (wk, mean 6 SD) Schober (cm, mean 6 SD) VAS (mm, mean 6 SD) SC-ODI (mean 6 SD) SC-QDS (mean 6 SD) Floor effects (%) Ceiling effects (%)
Patient group (test)
Patient subgroup (retest)
Pain-free group
114
60
65
64 (56.1%) 22 (36.7%) 30 (46.2%) 50 (43.9%) 38 (63.3%) 35 (53.8%) 49.9 6 9.2 49.6 6 9.3 50.1 6 8.7 18.3 6 6.4 19.5 6 7.1 d 4.52 6 0.81 d d 60.0 6 20.6 61.1 6 19.9 d 35.7 6 15.4 36.2 6 14.2 d 44.2 6 18.9 46.3 6 19.9 14.6 6 8.5 0 0 d 0 0 d
Abbreviations: SC, simplified Chinese; QDS, Quebec Back Pain Disability Scale; ODI, Oswestry Disability Index; SD, standard deviation.
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[13,29]. Thus, the SC-QDS was simple and quick for a Chinese-speaking population with LBP.
QDS score of the patients with LBP was significantly higher than that of the pain-free group (46.3 6 19.9 vs. 14.6 6 8.5 and P ! 0.0001) (Table 1).
3.4. Score distribution The distribution of scores for SC-QDS, VAS, and SCODI are shown in Table 1. The SC-QDS scores were well distributed with no floor or ceiling effects. Fig. 1 illustrates the frequency histogram of SC-QDS scores for the test group. 3.5. Reliability 3.5.1. Homogeneity The Cronbach a was 0.976 for the overall SC-QDS. Cronbach a ranged from 0.974 to 0.977 if an item was deleted, indicating excellent internal consistency. The itemetotal score correlations were significant (P ! 0.001) with Pearson’s coefficients ranging from 0.640 (item 16) to 0.898 (item 19). The detailed results of the itemetotal correlations and Cronbach a if an item was deleted are shown in Table 2. Our data showed that the SC-QDS items have good homogeneity. 3.5.2. Reproducibility The average interval between test and retest was 7.2 days (range: 5e8 days). The ICC of testeretest reliability was excellent and reached 0.987 (95% CI 0.978e0.992). The BlandeAltman plot (Fig. 2) shows the differences between measures from the two test sessions against the mean of the two sessions for each patient. The limits of agreement ranged from 9.0 to 8.8. No systematic bias between test and retest SC-QDS total scores was found, indicating good testeretest agreement. 3.6. Validity 3.6.1. Discriminative validity The SC-QDS scores between the randomly selected 60 patients in the retest group and the 65 pain-free individuals were significantly different. As expected, the mean SC-
Fig. 1. Distribution of the SC-QDS score (test group, n 5 114).
3.6.2. Construct validity The associations between SC-QDS and VAS or SC-ODI are presented in Table 3. Construct validity assessed by Pearson’s correlation coefficients between SC-QDS and SC-ODI or VAS indicated that the SC-QDS was significantly correlated with the SC-ODI (r 5 0.901 and P ! 0.0001) and VAS (r 5 0.770 and P ! 0.0001) in the test section (n 5 114). Thus, the SC-QDS had good construct validity.
4. Discussion The QDS is a back-specific, self-report outcome measure for patients with LBP, which contains 20 items in six domains (bed/rest, sitting or standing, ambulation, movement, bending/stooping, and handling large or heavy objects) to assess functional ability in daily life [9,10]. The original QDS is proven to have satisfactory psychometric properties [9,10]. When a questionnaire is considered for use in a new country, culture, or language, it must not only be well translated linguistically and appropriately adapted culturally but must maintain the original psychometric properties of the source version [30]. The QDS has been cross-culturally adapted into several different versions, with its related psychometric properties being successfully maintained (summarized in Table 4). In recent years, Chinese spinal surgeons, physicians, and other health care professionals have given more attention to heath-related quality-of-life issues that may impact their patients. As a result, the need for a method to accurately assess the Chinese-speaking patients’ perspective of the impact of LBP has risen. This study aimed to develop a simplified Chinese QDS and validate it for patients with LBP in mainland China. Psychometric testing of the resultant SC-QDS demonstrated its reliability and validity in measuring the functional status of Chinese-speaking patients with LBP. In particular, the score distribution of SC-QDS was satisfactory and there were no floor or ceiling effects. No patients experienced difficulty completing the questionnaires. Moreover, the SC-QDS had a 92% overall completion rate, whereas section 8 of the SC-ODI (sexual activity) had a low response rate. This low response rate may reflect the very private nature of sexual activity in the Chinese culture. Such missing responses can result in inaccurate assessments. Our results showed that the SC-QDS was simple to use, quickly self-completed, and had good clinical utility. According to previous reports, all different language versions of QDS possess good internal consistency with high Cronbach a range (0.92e0.96) [9,17,19e24]. The
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Table 2. Itemetotal score correlations of each item and Cronbach a if an item was deleted from the SC-QDS Itemetotal score correlation SC-QDS item Get out of bed Sleep through the night Turn over in bed Ride in a car Stand up for 20e30 min Sit in a chair for several hours Climb one flight of stairs Walk a few blocks (300e400 m) Walk several kilometers Reach up to high shelves Throw a ball Run one block (about 100 m) Take food out of the refrigerator Make your bed Put on socks (pantyhose) Bend over to clean the bathtub Move a chair Pull or push heavy doors Carry two bags of groceries Lift and carry a heavy suitcase
r
P-value
Cronbach a if an was item deleted
0.751 0.856 0.849 0.885 0.879 0.860 0.847 0.863 0.865 0.869 0.837 0.725 0.810 0.777 0.846 0.640 0.854 0.882 0.898 0.828
!0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001 !0.0001
0.976 0.975 0.975 0.974 0.975 0.975 0.975 0.975 0.975 0.975 0.975 0.976 0.975 0.976 0.975 0.977 0.975 0.974 0.974 0.975
SC-QDS internal consistency was excellent, with the Cronbach a reaching 0.976, higher than that of all other versions: original (0.96) [9], Dutch (0.95) [17], Iranian (0.92) [19], Brazilian (0.97) [20], Turkish (test, 0.941 and retest, 0.957) [21,22], Polish (0.95) [23], and Korean (0.92) [24]. It was noteworthy that the SC-QDS Cronbach a was limited to a very small range (0.974e0.976) if an item was deleted. The itemetotal score correlations were used to quantitate the strength of correlation between each item and the total scores [31]. Moreover, each item was significantly correlated to the overall questionnaire (Pearson’s coefficients ranging from 0.640 [item 16] to 0.898 [item 19]), indicating that each item assessed the same aspect
of the construct. The itemetotal correlations of SC-QDS were higher than those of the original [9], Dutch [17], French [18], and Turkish [22] versions. To evaluate testeretest reliability, it is generally suggested that the time period between repeated administrations should be long enough to prevent recall but short enough to ensure that clinical change has not occurred. No definitive time interval has been experimentally determined, and 1 or 2 weeks are often considered to be appropriate [25]. The time intervals used for the reliability test in other studies were 3e4 days (Brazilian) [20], 1 day (Iranian and Turkish) [19,22], 2 days (Polish) [23], 1e14 days with an average of 3.8 days (original study) [9], 1 week (Dutch)
Fig. 2. BlandeAltman plot for testeretest agreement of the SC-QDS. The differences between patients for the measures from the two test sessions were plotted against the mean of the two sessions for the SC-QDS total scores. The dashed line indicates the 95% (61.96 standard deviation) limits of agreement.
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Table 3. Pearson’s correlations between SC-QDS and SC-ODI/VAS in the test group (n 5 114)
correlation between the scores of SC-QDS and SC-ODI; the Pearson’s correlation coefficient was 0.870 (P ! 0.0001), similar to that of the Polish version (r 5 0.841 in test and r 5 0.866 in retest) [23] but higher than that of the original English (r 5 0.77) [9], the Iranian (r 5 0.76) [19], the Turkish (r 5 0.67 in test and r 5 0.68 in retest) [22], and the Korean versions (r 5 0.718 in test and r 5 0.690 in retest) [24]. Previous studies indicated that QDS is significantly correlated to patients’ pain severity, with the Pearson’s correlation coefficient between QDS and VAS ranging from 0.37 to 0.75 [18,20e22,24]. The variation in results from previous studies is not surprising given the multidimensional complexity of pain, especially in chronic form. Our study demonstrated that SC-QDS and VAS are significantly correlated; the test (r 5 0.770) and retest (r 5 0.754) were even higher than those previously reported. In addition, the high correlation between the SC-QDS and the SC-ODI/VAS indicated good construct validity for the SC-QDS. In other published studies that evaluated the different versions of QDS, the patient population size ranged from 32 [18] to 130 [20] (Table 4). Our study included 114 patients coming from different areas of mainland China; however, there may still be some potential patient selection bias. Although the number of patients in our study was relatively small, it was sufficient by statistical analysis requirements. Our study only included patients with LBP O6 weeks, and none of the patients had received surgery. The patient population included in this study was similar to those used in other studies [17e24], which might represent a common limitation shared among these studies. Considering the exceedingly large population in China, we believe that an SC-QDS study using a larger population in mainland China is still needed. Responsiveness, defined as the ability to detect clinically important changes over time, is a critical property of medical questionnaires [25]. The study by Demoulin et al. [32] demonstrated that QDS was responsive and showed
SC-QDS Test score VAS SC-ODI
r
95% CI
P-value
0.870 0.901
0.796e0.923 0.867e0.934
!0.0001 !0.0001
Abbreviation: VAS, visual analogue scale.
[17], and 2 weeks (Korean) [24]. In our study, 60 patients were randomly selected to complete the SC-QDS questionnaire twice and the time interval for the recompletion of SC-QDS was 1 week. The reasoning for this time included the belief that a 1-week interval ensured that patients who received medical treatment would not have experienced an obvious clinical change and the fact that 1 week is the time that patients are required to wait for surgery, thereby ensuring that patients arranged for surgery would not be omitted from the reliability evaluation. For the analysis of SC-QDS testeretest reliability, the high value of ICC (0.987) revealed an excellent reproducibility. Comparison with other versions showed that the SC-QDS ICC was higher than that of the original (0.92) [9], Dutch (0.90) [17], Iranian (0.86) [19], Brazilian (0.93) [20], Turkish (0.92) [22], Polish (0.93) [23], and Korean (0.91) [24] versions. To our knowledge, no previous study has tested the psychometric property of discriminative ability for the different QDS versions [9,17e24]. However, the SC-QDS was tested and found to have discriminative validity (divergent construct validity), as evidenced by higher scores for patients with LBP than for pain-free controls. ODI and RMDQ are two of the most frequently applied instruments to evaluate QDS construct validity. Previous studies showed that QDS is significantly correlated to RMDQ (Pearson’s correlation coefficient range: 0.60e0.91) [9,17,19,20]. In our study, SC-ODI was selected as the comparison measure to evaluate the construct and concurrent validity of the SC-QDS. We found a significant and strong
Table 4. Summary of evidence on reliability and validity of various versions of the QDS for LBP Reliability Testeretest QDS versions English (Canada) [9], 1995 French (Canada) [9], 1995 French (France) [18], 2002 Iranian [19], 2006 Brazilian [20], 2009 Turkish [21], 2005 Turkish [22], 2009
Validity
Internal consistency
n
ICC
n
Cronbach a
n
Tested variable
Pearson’s correlation,r
52 46 d 31 54 d 100
0.93 0.88 d 0.86 0.93 d 0.92
123 102 d 100 54 83 100
0.95 0.96 d 0.92 0.97 0.93 0.94 (test)
130 112 32 100 54 83 100
ODI ODI VAS ODI VAS VAS VAS
0.77 0.83 0.45 0.76 0.75 0.46 0.37 (test) 0.44 (retest) 0.67 (test) 0.68 (retest) 0.84 (test) 0.87 (retest) 0.718 0.647
0.96 (retest) Polish [23], 2011
85
0.93
111
Korean [24], 2011
59
0.91
80
0.95 (test) 0.95 (retest) 0.92
Abbreviations: n, Sample size; ICC, intraclass correlation coefficient.
ODI 111
ODI
80
ODI VAS
X. Wei et al. / Journal of Clinical Epidemiology 65 (2012) 1321e1328
reasonable interpretability after a multidisciplinary treatment. Wilhelm et al. [33] showed that, in a sample of chronic LBP sufferers, the QDS was more sensitive to clinical change than was the Dallas Pain Questionnaire. It was recommended that for the QDS, a 30% change (20 points) from baseline may be considered as clinically meaningful improvement when comparing before and after measures for individual patients [34]. However, in this study, we did not report the responsiveness of SC-QDS because of the short time follow-up and lack of head-to-head comparative data. Other published studies (involving the Turkish, Brazilian, French, Korean, Polish, Iranian, and Dutch versions) similarly did not report the responsiveness of QDS, which is a shared shortcoming. Comparative study of SC-QDS responsiveness with other instruments, such as SC-ODI and SC-RMDQ, is under way by our group. 5. Conclusions The English QDS was successfully translated into SC and culturally adapted for use in mainland China. The SC-QDS is easy to understand and quick to complete. The psychometric properties of the original version are maintained. The SC-QDS has good homogeneity, reproducibility, and discriminative and construct validity. We suggest that the SC-QDS can be widely used for assessing function in patients with LBP in mainland China. Acknowledgments No grants or technical or financial support were used for this study. So none needs to be acknowledged. No conflicts of interest exist for any of the study’s authors. Appendix supplementary data Supplementary data related to this article can be found online at http://dx.doi.org/10.1016/j.jclinepi.2012.06.007. References [1] Shelerud RA. Epidemiology of occupational low back pain. Clin Occup Environ Med 2006;5:501e28. [v]. [2] Merkesdal S, Mau W. Prediction of costs-of-illness in patients with low back pain undergoing orthopedic outpatient rehabilitation. Int J Rehabil Res 2005;28:119e26. [3] Jin K, Sorock GS, Courtney T, Liang Y, Yao Z, Matz S, et al. Risk factors for work-related low back pain in the People’s Republic of China. Int J Occup Environ Health 2000;6:26e33. [4] Barrero LH, Hsu YH, Terwedow H, Perry MJ, Dennerlein JT, Brain JD, et al. Prevalence and physical determinants of low back pain in a rural Chinese population. Spine 2006;31:2728e34. [5] Costa LO, Maher CG, Latimer J. Self-report outcome measures for low back pain: searching for international cross-cultural adaptations. Spine 2007;32:1028e37.
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