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Predicting work status following interdisciplinary treatment for chronic pain
European Journal of Pain 8 (2004) 351–358 www.EuropeanJournalPain.com
Predicting work status following interdisciplinary treatment for chronic pain Kevin E. Vowles b
a,*
, Richard T. Gross b, John T. Sorrell
a,1
a Department of Psychology, West Virginia University, PO Box 6040, Morgantown, WV 26506-6040, USA Oasis Occupational Rehabilitation and Pain Management, PO Box 4013, Morgantown, WV 26504-4013, USA
Received 18 February 2003; accepted 28 October 2003 Available online 17 January 2004
Abstract The effectiveness of interdisciplinary treatments for chronic pain is well established. In general, these treatments decrease psychosocial distress and increase physical abilities. Further, return to work rates following interdisciplinary treatment tend to be quite high. Previous studies have highlighted a number of factors that individually influence return to work rates; however, there is a need for more comprehensive and unified models that allow an evaluation of the inter-relations among these factors. The present investigation examined how demographic and treatment outcome variables interacted to influence post-treatment return to work rates in a sample of individuals with chronic pain following interdisciplinary treatment. Results indicated that patient age, lifting ability, pain duration, depression level, and reported disability were individually related to return to work; however, when these variables were evaluated relative to one another, level of depression and patient age had the best ability to predict post-treatment work status. These results add to the literature by specifically highlighting post-treatment factors that best discriminate patients who had returned to work from those that had not. Furthermore, they provide evidence that general emotional distress is perhaps the most important predictor of work status following treatment. Ó 2003 European Federation of Chapters of the International Association for the study of Pain. Published by Elsevier Ltd. All rights reserved. Keywords: Chronic pain; Interdisciplinary treatment; Return to work
1. Introduction Available research indicates that interdisciplinary treatment programs for chronic pain are effective. Treatment completers typically report decreased pain intensity, lessened depression and pain-related anxiety, improved levels of disability and pain coping skills, decreased utilization of healthcare facilities and medications, and increased physical and work-related abilities (Flor et al., 1992; Curtis et al., 1994; Hubbard et al., 1996; Gatchel and Turk, 1999; McCracken and Gross, 1998; Morley et al., 1999; McCracken et al., 2002; *
Corresponding author. Tel.: +1-304-293-2001; fax: +1-304-2936606. E-mail address: [email protected] (K.E. Vowles). 1 Present address: VA San Diego Healthcare System, 3350 La Jolla Village Drive (116B), San Diego, CA 92161, USA.
Vowles and Gross, 2003; Wright and Gatchel, 2002). Further, a recent review by Turk (2002) suggested that interdisciplinary programs are more cost-effective than alternative pain control treatments (i.e., spinal cord stimulator implantation, implantable drug delivery systems, ‘‘conservative’’ care, and surgery) while achieving equal or greater efficacy. One of the most important indicators of ‘‘successful’’ treatment outcome is return to work (Tait, 1999), likely because of the high financial cost of chronic pain in terms of lost occupational productivity and disability payments (Gatchel and Mayer, 2000), as well as the urging of third-party payers (e.g., United States WorkmanÕs Compensation) to reduce these costs. In general, interdisciplinary treatments effectively improve patientsÕ occupational functioning, with success being documented in both rates of return to work (Flor et al., 1992; Cutler et al., 1994) and duration of actual hours worked
1090-3801/$30 Ó 2003 European Federation of Chapters of the International Association for the study of Pain. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ejpain.2003.10.009
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(Hubbard et al., 1996). Given the effectiveness of these treatments, as well as their expense, a number of investigators have attempted to isolate the factors that are associated with increased occupational functioning. Three types of variables primarily have been evaluated: physical, demographic/socioeconomic, and psychosocial. Across studies, physical factors, such as improvements in strength, endurance, or flexibility appear to have little relation to return to work rates following interdisciplinary treatment (Fishbain et al., 1993; Hildebrandt et al., 1997). These findings mirror other studies within chronic pain, which almost uniformly indicate that pre-treatment levels of physical capacity and treatment-mediated changes in physical capacity have minimal discernable effect on treatment outcomes (Burton et al., 1995; McCracken et al., 2002; Vowles and Gross, 2003). The only notable exception to this finding was reported by Matheson et al. (2002), who found that oneÕs ability to lift weight from the floor to waist level had a small, but significant, relation to return to work rates. Conversely, a number of important demographic and socioeconomic factors that are related to treatment outcome have been identified. Individuals who return to work following treatment tend to be younger males (Fishbain et al., 1993). Further, return to work rates are higher among individuals who have been off work for shorter periods of time (Fishbain et al., 1993; Hildebrandt et al., 1997) and who have higher levels of education (Fishbain et al., 1997a). Similarly, Stratton et al. (1996) reported that younger age, greater level of education, and shorter pain duration were important predictors of eventual return to work although their investigation did not include a specific treatment component. Across studies, psychosocial variables appear to have the strongest influence on return to work rates. Lower pre-treatment levels of perceived disability due to pain and lower pain intensity increase the probability that a patient will return to work, while elevated scores on Scale 3 of the Minnesota Multiphasic Personality Inventory, which generally assesses somatic complaints, are a negative influence (Gatchel et al., 1995). With regard to changes in psychosocial variables over the course of treatment that are predictive of outcome, individuals who experience greater reductions in perceived disability and depression are more likely to return to work compared to patients who experience lesser reductions (Hildebrandt et al., 1997). In sum, those who report higher psychosocial distress before treatment or who exhibit lesser changes in distress over the course of treatment tend not to return to work. Previous investigations have identified a number of important factors that individually influence return to work rates. However, given the complexity in determining these rates in individuals with chronic pain, there
is a need for the development of more comprehensive models which take into account the interaction and collective influence of these variables on return to work. Therefore, the present investigation sought to evaluate the relation of a broad range of demographic, physical, and psychosocial factors to post-treatment return to work status in individuals with chronic pain using both univariate and multivariate data analytic strategies. Furthermore, we utilized data collected at the conclusion of a treatment program in order to specifically determine how patientÕs physical and psychosocial functioning at this point in treatment was related to work status.
2. Materials and methods 2.1. Participants Individuals who had completed an interdisciplinary treatment for chronic pain were included in the present analyses. Potential patients for inclusion in the analyses included 183 patients who entered treatment out of 320 total patients assessed over a four-year period (i.e., 1999–2002). For an offer of admission to the treatment program, individuals must have had pain in excess of 90 days, exhibited no psychotic symptomology, and must have had an explicit goal of improving functioning and/ or returning to work. Furthermore, individuals in need of surgical interventions were not admitted to the program. Finally, insurance approval and patient consent were required. Of the patients who accepted an offer of admission into the program, 30 (16.4%) were discharged because of compliance or issues related to non-participation and an additional 15 (8.2%) discontinued treatment for other reasons (e.g., illness, death in the family). Therefore, 138 patients (41% female) completed the treatment program. Treatment completers did not differ from non-completers with regard to age, pain duration, or pre-treatment levels of depression, pain intensity, pain-related fear, pain disability, and demonstrated physical capability based on one-way Analyses of Variance. Further, v2 analyses indicated that gender and marital status classifications were proportional among completers and non-completers. Mean values were used to replace missing data; in all, 13 individuals were missing one point of data, two were missing two points, and two were missing three points. On average, participants were 40.5 years of age (SD ¼ 8:3 years) and married (67.4%; 13.0% single; 17.4% divorced/separated; and 2.2% widowed). Further, mean pain duration was 21.5 months (SD ¼ 17:7 months; range 3–115 months) with low back pain being the most common complaint (68.1%; 15.9% neck; 21.7% upper extremity; and 26.1% lower extremity). In all, 37.7% of the sample endorsed more than one area
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of pain. Since the date of initial injury, none of the participants had successfully returned to work; therefore, for the purposes of the present investigation, duration of injury and time off of work were identical. All patients had sustained work-related injuries that were contributing to their chronic pain problem and were unemployed and receiving WorkmanÕs Compensation benefits at the onset of treatment. With regard to job status, approximately one-half (53%) of the patients who were enrolled in the treatment program had a job available with their prior employer following treatment. Across patients, this availability of a job did not guarantee them a position or a job offer once treatment had concluded. Instead, they had to demonstrate the physical ability to perform the job, as well as a desire to return to it. 2.2. Treatment program Participants were enrolled in an interdisciplinary treatment program based on a sports medicine approach to rehabilitation similar to the one described by Mayer and Gatchel (1988). The program was 4–6 weeks in length; participants attended approximately 6 h/day, 5 days/week. Patients averaged 20.4 days (SD ¼ 4:2 days) in treatment; therefore, the majority of patients completed the 4-week treatment program. Each day, participants attended 3 h of psychoeducational groups and 3 h of physical and occupational therapy. Patients had daily contact with psychology, physical therapy, and occupational therapy staff members, and were seen by a rehabilitation physician at least once per week. In addition to facilitating return to work, the treatment program also sought to increase functional capacity, decrease affective distress, and educate patients about the chronic pain process. 2.3. Measures Prior to completing the treatment program (i.e., 1–2 days), patients completed a number of self-report measures and an assessment of physical capability. Variables selected for inclusion for analysis were based on prior research indicating both the relation of individual variables to return to work rates and to treatment outcome in general, as well as theoretical models of chronic pain distress and disability, as discussed below. 2.3.1. Self-report psychosocial measures 2.3.1.1. Beck Depression Inventory-II. Associations between pain and depression have been found consistently in both acute and chronic pain populations (Fishbain et al., 1997b; Rethelyi et al., 2001). Specifically, depression appears to be associated with more frequent and severe pain reports, in both chronic pain (Krause et al., 1994) and acute pain (Bengtson et al., 1996), and has a
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negative influence on return to work rates (Gatchel et al., 1995; Hildebrandt et al., 1997). The Beck Depression Inventory-II (BDI-II; Beck et al., 1979) is a 21-item self-report assessment designed to measure clinically relevant cognitive, affective, and vegetative symptoms of depression. Participants rate the degree to which they endorse different depressive symptoms on a 1–4 point Likert-type scale. The BDI-II has demonstrated good psychometric properties (Beck et al., 1988). 2.3.1.2. McGill Pain Questionnaire-Short Form. The total score of the McGill Pain Questionnaire-Short Form (MPQ-SF; Melzack, 1987) was used to assess pain intensity. The psychometric properties of the measure are well established within a chronic pain population, and it has been used widely in both research and clinical settings (Melzack and Katz, 2001). 2.3.1.3. Pain Anxiety Symptoms Scale. Over the past two decades, increasing attention has been paid to the role that pain-related anxiety plays in disability among chronic pain patients. One of the most frequently used measures of pain-related anxiety is the Pain Anxiety Symptoms Scale (PASS; McCracken et al., 1992). A total score, as well as four subscale scores, are derived from the measureÕs 40 items and research supports its psychometric properties and utility within chronic pain (McCracken et al., 1996, 1992; Burns et al., 2000; Strahl et al., 2000). In order to retain statistical power, the present analyses used only the total score of the PASS. 2.3.1.4. Pain Disability Index. The Pain Disability Index (PDI) is a 7-item measure developed to assess the perceived effect that chronic pain has on oneÕs daily functioning (Pollard, 1984). Prior research has indicated that scores on the PDI are reliable and are related to painrelated disability, pain intensity, and general psychological distress (Jerome and Gross, 1991; Tait et al., 1990; Chibnall and Tait, 1994). The amount of perceived disability arising from pain is rated for a number of activities, in areas such as occupation, recreation, social interactions, and self-care, on a 0–10 Likert-type scale, with 0 equivalent to no disability and 10 equal to complete disability. 2.3.2. Physical capacity measures Two measures of physical ability were collected as part of a larger functional capacity examination (FCE). An FCE is designed to assess an individualÕs physical ability to perform vocational activities and is used as a measure of work capability (Snook, 1978). Similar measures have been used in previous experiments and provide an index of actual physical ability (Fishbain et al., 1994; Geisser et al., 2000; McCracken et al., 2002). For the purposes of the present analyses, the amount of
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weight that each participant could lift from the floor to waist level and from waist to shoulder level at posttreatment was utilized. These measures were selected because they appear to be relatively reliable across time and assessor (Smith, 1994; Isernhagen et al., 1999; Gross and Battie, 2002) and, as noted earlier, recent research suggests that at least the floor to waist lift has a significant, albeit moderate, relation to return to work (Matheson et al., 2002). 2.3.3. Return to work For the purposes of the present study, individuals who successfully completed the treatment program were contacted 6 months after treatment completion to ascertain whether they had returned to work since concluding treatment. Patients who reported working on a part-time or full-time basis were coded as having returned to work, as were individuals in job retraining or education programs. These latter two variables were coded as return to work because they represent levels of functioning that mimic in some ways the work environment and elicit work-related behaviors in patients (i.e., patients have to go to some place on a daily basis and keep functioning at relatively consistent levels). Patients who had retired, were on permanent disability, or who were in active job search were coded as not having returned to work. Post-treatment work data could not be ascertained for 11 individuals (8.0%); therefore, additional analyses only included the data of 127 persons. Although a longer follow-up period would have allowed better longitudinal data, this short-term follow-up period was used in order to increase the probability that the actual effect of the treatment program was assessed. Work status after a longer period of time has passed likely is affected by a number of variables (e.g., economic conditions, job availability, other illnesses; Turk, 2002), which are not addressed nor controlled for by the treatment program.
3. Results A total of 90 individuals (70.9%) reported having returned to work within 6 months of treatment completion. Of those who had returned to work, 5.6% (N ¼ 5) reported working part-time, 5.6% (N ¼ 5) were involved in an educational program, and 1.1% (N ¼ 1) reported being involved in job retraining, while the remaining 87.7% (N ¼ 79) reported working full-time. With regard to individuals who reported not working, 45.9% (N ¼ 17) remained in job search and 10.8% (N ¼ 4) were either retired or were classified as permanently disabled by United States Social Security. The remaining 43.2% (N ¼ 16) reported having no plans to return to work in the immediate future. Descriptive data regarding demographic and outcome measures are included in Table 1. Although the efficacy of functional restoration programs was not the focus of the present analyses, it is important to note that over two-thirds of treatment completers returned to work, or were involved in some type of retraining, at the time of follow-up. This is somewhat above the return to work rates reported in the meta-analyses performed by Cutler et al. (1994) and Flor et al. (1992) and is yet another indication regarding the effectiveness of treatments that specifically target a population of individuals who have sustained workrelated injuries. As a preliminary method of investigating the relation of the dependent measures to work status, zero-order correlation coefficients first were calculated. As illustrated in Table 2, individuals reporting higher levels of depression, pain intensity, and pain-related disability at post-treatment were less likely to return to work, as were older persons and those who were able to lift lower amounts of weight from the floor to waist level at the end of treatment. These five variables were retained for a subsequent discriminant analysis. With regard to other indicated correlations, measures of pain, psychosocial
Table 1 Means (SDs) of outcome measures across groups Variable
Group Working
Not working
Combined
Age (years) Education (years) Pain duration (months) BDI-II MPQ-SF PASS PDI Floor to waist lifting (lb) Waist to shoulder lifting (lb)
39.1 11.7 21.0 12.0 16.3 67.9 25.6 58.2 52.6
42.8 11.6 22.9 18.5 20.5 78.2 33.0 51.9 44.3
40.2 11.7 21.6 13.9 17.5 70.9 27.8 56.4 50.2
(7.9) (1.3) (19.5) (8.1) (9.2) (28.1) (11.7) (28.5) (18.5)
(8.6) (0.9) (14.5) (10.3) (8.5) (33.7) (12.2) (25.2) (16.9)
(8.2) (1.2) (18.1) (9.2) (9.2) (30.1) (12.3) (27.6) (18.3)
Note. N ¼ 127. BDI-II, Beck Depression Inventory-II; MPQ-SF, McGill Pain Questionnaire-Short Form; PASS, Pain Anxiety Symptoms Scale; PDI, Pain Disability Index.
– –
Note. , p 6 0:05; , p 6 0:01; , p 6 0:001; N ¼ 127; BDI-II: Beck Depression Inventory-II; MPQ-SF: McGill Pain Questionnaire-Short Form; PASS: Pain Anxiety Symptoms Scale; PDI: Pain Disability Index.
)0.25** )0.51** )0.09 0.004 )0.23** )0.27** )0.07 )0.20* 0.67*** – )0.19* )0.46** 0.14 )0.02 )0.20* )0.27** )0.10 )0.20* – 0.002 )0.09 )0.02 – 0.13
)0.08 )0.08 –
)0.01 0.02 )0.001 )0.02 –
0.06 0.01 )0.19* 0.03 0.54*** –
)0.21* )0.02 )0.03 )0.07 0.54*** 0.43*** –
0.04 )0.14 )0.19* 0.02 0.46*** 0.42*** 0.39*** –
)0.10 )0.21*
10
0.05 )0.06
1
– 1. Work status (1, working; 2, not working) 2. Age (years) 3. Gender (1, male; 2, female) 4. Education (years) 5. Pain duration (months) 6. BDI-II 7. MPQ-SF 8. PASS 9. PDI 10. Floor to waist lifting (lb) 11. Waist to shoulder lifting (lb)
Table 2 Correlations among work status, demographic, and treatment outcome measures
5 4
)0.02
3 2
0.21
6
0.32***
7
0.21*
8
0.16
9
0.27**
11
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Table 3 Percentage of correct and incorrectly classifications for post-treatment work status Work status
Working Not working
Predicted work status from initial function n
Working
Not working
61 18
46 (75.4%) 6 (33.3%)
15 (24.6%) 12 (66.7%)
distress, and physical functioning were generally intercorrelated, as is often the case in studies in this area. The final phase of data analysis involved a stepwise discriminant analysis to evaluate the value of patientÕs age and post-treatment levels of depression, pain intensity, pain-related disability, and floor to waist lifting ability to predict participantsÕ work status. A stepwise analysis was utilized rather than a more inclusive fullmodel analysis, in order to identify those measures that were the best predictor(s) of post-treatment work status. The calculated discriminant function was statistically significant, WilksÕ k ¼ 0:72, v2 ð2Þ ¼ 24:57, p 6 0:001. Two variables entered into the equation, depression and participant age; the correlation between these measures and the discriminant function was r ¼ 0:80 and r ¼ 0:51, respectively. The canonical correlation, which measures the relation between the function and variable set, was equal to 0.53, indicating that approximately 28% of the variance in post-treatment work status was accounted for by these two variables. With regard to the actual results of the classification, 73.4% of participants were correctly classified. Table 3 lists specific classification results. In order to cross-validate the classification results, the discriminant analysis was repeated utilizing the U-method, which classifies each individual case in the dataset using a discriminant function derived using all cases other than that case. This method of analyses provides a preliminary validation of classification results that is less susceptible to the inflated accuracy that occurs when the discriminant function derived from a sample is used to classify that same sample (Tabachnick and Fidell, 2001). The cross-validated function correctly classified 72.2% of participants; this function incorrectly classified one more participant than did the original function.
4. Discussion The purpose of the present study was to specifically evaluate a number of factors that have empirical or theoretical relations to return to work in a sample of injured workers experiencing long-term pain. Further, we not only hoped to identify the factor or factors that clinicians and researchers can evaluate at the conclusion of treatment to predict who will return to work and who
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will not, but also to better understand what patient variables would be most important treatment foci to help patients re-establish employment. Within our sample, five factors were significantly correlated with 6-month post-treatment work status and were tested in a subsequent discriminant analysis. Two of these measures, depression and participant age, entered into the equation and accounted for a significant amount of variance. Almost two-thirds of the individuals who completed the treatment program returned to work. Further, psychosocial factors were more strongly related to posttreatment work status than were physical capacity variables, which replicates the findings of a number of investigators (Fishbain et al., 1993; Hildebrandt et al., 1997; McCracken et al., 2002; Vowles and Gross, 2003). Perhaps the most interesting finding of the present investigation was that a general measure of depressive symptomology and psychological distress (the BDI-II) was most highly correlated with the discriminant function predicting post-treatment work status. This result diverges somewhat from previous findings, which have indicated that pain-specific measures, such as fear of pain, fear-avoidance beliefs, perceived disability, and to a lesser extent pain severity, have a greater relation with treatment outcome in individuals with chronic pain (McCracken and Gross, 1998; McCracken et al., 2002; Vowles and Gross, 2003). The present findings add to this body of literature by indicating that depression may have a greater overall impact on some aspects of functioning; in particular, post-treatment job status. This difference in findings likely is accounted for by the fact that successfully participating in gainful employment consists of a number of behaviors and can be affected by a multitude of complex factors, such as economic environment, peer relations, and job availability. Although pain-specific measures likely influence whether or not an individual will succeed at returning to work after a chronic pain treatment program, the effect of these measures may be overshadowed by the effect of depression, which can adversely affect diverse areas such as pain tolerance (Rethelyi et al., 2001; Carter et al., 2002) and physical and social functioning (Kaplan and Sadock, 1998) in the absence of chronic pain. In fact, recent evidence suggests that depression can have significant detrimental effects on work attendance and productivity in individuals without chronic pain. Specifically, Druss et al. (2001) found that workers who were depressed were twice as likely to miss work and seven times as likely to have decreased productivity at work relative to their non-depressed counterparts. Given the wide-ranging effects of depression on functioning in general, and in chronic pain in particular (Robinson and Riley, 1999), it is not surprising an interdisciplinary functional restoration treatment was not as effective with individuals experiencing elevated levels
of depressive symptomology. It is possible that the sample complaining of elevated depression may need additional intervention, or an intervention specific to depression, to achieve similar results. The relevance of age in predicting who will return to work has been indicated before (Fishbain et al., 1993). The present results regarding age serve only to replicate this finding. From a treatment perspective, however, this result is somewhat problematic. From one point of view, it could be argued that these data indicate that older individuals who have been injured at work should not undergo treatment because such interventions appear unlikely to affect this particular variable. This argument, however, is flawed because we do not yet know why older individuals are less likely to return to work and it discounts the benefits of treatment on depressive symptoms (and other psychological factors) irrespective of work status following treatment. It may be that older patients prefer to retire, have poorer access to jobs, are less likely to be hired, or are less likely to be selected by employees to be retrained. Although any of these reasons are plausible, we are unaware of any studies investigating which, if any, are empirically verifiable. In addition to patient variables and characteristics of employment, there may be treatment variables that need to be adjusted to better serve older patients in returning to work following treatment. In all, the calculated discriminant function indicated that patientÕs post-treatment level of depression and age accounted for approximately 28% of the variability in post-treatment job status. Although this amount of variance leaves over two-thirds of the variance unaccounted for, the present findings are nonetheless important because level of depression is something that can be effectively treated. The other important variables in determining post-treatment work status likely consist of many job-related and environmental factors, such as job availability, rates of unemployment, local economy, and job satisfaction, which are not addressed by interdisciplinary treatment programs. The same logic obviously applies to demographic variables (e.g., age, gender) as well. Therefore, it is important to identify those variables that affect outcomes that can be effectively addressed in treatment. Level of post-treatment depression represents one of these factors, and there are effective treatments available. Within interdisciplinary functional restoration treatments, patients engage in many new, ‘‘healthy’’ behaviors, such as increased physical activity, social contact, work readiness, and recreational activities that may be incompatible with depressive behaviors, as evidenced by literature concerning depression (Lejuez et al., 2001). Given that selfreported depression had the greatest relation with work status following treatment, increasing ‘‘healthy’’ behaviors in treatment programs for chronic pain may be of the utmost importance.
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With regard to limitations, the relatively small number of participants included in the present study leads to a reduction in the power of the analyses and decreases the possibility of generalization to other individuals in treatment for chronic pain. The collection of data from a larger pool of participants would allow these issues to be addressed. Second, despite the initial inclusion of overt measures, only self-report measures were included in the final discriminant analysis leading to the possibility of many types of well-documented errors associated with this type of data. Perhaps further investigations could include additional measures of physical capacity, or other overt measures of behavior, to determine the utility of such variables. We also did not collect data regarding the types of jobs that patients return to following the program, nor the physical demand of those jobs. This does not allow us to assess for differences with regard to the physical demand of the post-treatment job. Finally, the results are limited by the statistical methods used. The model of post-treatment functioning for individuals with chronic pain is complex; therefore, the use of more sophisticated data analytic techniques, which allow the evaluation of multidirectional models (e.g., path analysis and structural equation modeling), may be of significant utility in elucidating the exact mediators of chronic pain treatment outcome. A few additional comments regarding the present study are necessary. First, these data generally support the efficacy of this type of treatment as a means of improving the probability of return to work. This sample, however, was selected based on their desire to improve functional ability; therefore, these data do not necessarily generalize to individuals with chronic pain who do not espouse such goals, nor to individuals who did not complete treatment. Nonetheless, given the accumulating literature supporting such interventions (see Turk, 2002 for a review), it is reasonable to conclude that these types of treatment are effective for a sizable proportion of individuals with chronic pain. The second issue pertains to the nature of the WorkmanÕs Compensation system in the United States. Within this system, there are definite contingencies on patients to return to work, which include the fact that they receive only a percentage of their previous wage and have to continue to provide documentation of their disability over time in order to continue to receive benefits. It is likely these contingencies, which are inherent in the system, aided the outcome of the present study. It is not possible to determine the extent to which they helped and it should be noted that this was a treatment refractory sample who were, on average, almost 2 years post-injury and who had not returned to work on their own or as a result of previous interventions. Therefore, it can be argued that the treatment program acted as a catalyst, or at very least helped
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motivate patients, to return to work. In other socioeconomic systems, there may be no contingencies for patients to return to work or alternative contingencies that exert stronger influence on patientÕs behavior to do other things (e.g., remain on disability). From a behavioral perspective, the lack of contingencies and/or stronger, more influential contingencies decreases the probability that patients will return to work. We have analyses that are currently underway from a similar treatment program in the United Kingdom which may allow some of these issues to be addressed. In sum, the findings of the present investigation add to the emerging complex model of treatment outcome for individuals with chronic pain. As indicated in previous studies, psychosocial measures were more predictive of treatment outcome than physical capacity measures. Furthermore, although previous investigations have found that pain-specific variables such as pain-related anxiety and fear-avoidance beliefs significantly predict other measures of distress and disability (e.g., pain severity, depression, and physical capacity), the current study extends these results to show that general distress, as measured by the BDI-II, significantly predicts post-treatment work status. That this general measure of distress was most associated with posttreatment work status underscores the effects that depression can have on oneÕs functioning and the clinical importance of addressing this area in treatment programs for chronic pain.
Acknowledgements The authors thank the entire staff at PSIMED and Oasis Occupational Rehabilitation and Pain Management for their support and assistance in the collection of data for this project. Thanks also to Stanley Cohen, Ph.D., for comments on an earlier draft of this manuscript.
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Predicting work status following interdisciplinary treatment for chronic pain Kevin E. Vowles b
a,*
, Richard T. Gross b, John T. Sorrell
a,1
a Department of Psychology, West Virginia University, PO Box 6040, Morgantown, WV 26506-6040, USA Oasis Occupational Rehabilitation and Pain Management, PO Box 4013, Morgantown, WV 26504-4013, USA
Received 18 February 2003; accepted 28 October 2003 Available online 17 January 2004
Abstract The effectiveness of interdisciplinary treatments for chronic pain is well established. In general, these treatments decrease psychosocial distress and increase physical abilities. Further, return to work rates following interdisciplinary treatment tend to be quite high. Previous studies have highlighted a number of factors that individually influence return to work rates; however, there is a need for more comprehensive and unified models that allow an evaluation of the inter-relations among these factors. The present investigation examined how demographic and treatment outcome variables interacted to influence post-treatment return to work rates in a sample of individuals with chronic pain following interdisciplinary treatment. Results indicated that patient age, lifting ability, pain duration, depression level, and reported disability were individually related to return to work; however, when these variables were evaluated relative to one another, level of depression and patient age had the best ability to predict post-treatment work status. These results add to the literature by specifically highlighting post-treatment factors that best discriminate patients who had returned to work from those that had not. Furthermore, they provide evidence that general emotional distress is perhaps the most important predictor of work status following treatment. Ó 2003 European Federation of Chapters of the International Association for the study of Pain. Published by Elsevier Ltd. All rights reserved. Keywords: Chronic pain; Interdisciplinary treatment; Return to work
1. Introduction Available research indicates that interdisciplinary treatment programs for chronic pain are effective. Treatment completers typically report decreased pain intensity, lessened depression and pain-related anxiety, improved levels of disability and pain coping skills, decreased utilization of healthcare facilities and medications, and increased physical and work-related abilities (Flor et al., 1992; Curtis et al., 1994; Hubbard et al., 1996; Gatchel and Turk, 1999; McCracken and Gross, 1998; Morley et al., 1999; McCracken et al., 2002; *
Corresponding author. Tel.: +1-304-293-2001; fax: +1-304-2936606. E-mail address: [email protected] (K.E. Vowles). 1 Present address: VA San Diego Healthcare System, 3350 La Jolla Village Drive (116B), San Diego, CA 92161, USA.
Vowles and Gross, 2003; Wright and Gatchel, 2002). Further, a recent review by Turk (2002) suggested that interdisciplinary programs are more cost-effective than alternative pain control treatments (i.e., spinal cord stimulator implantation, implantable drug delivery systems, ‘‘conservative’’ care, and surgery) while achieving equal or greater efficacy. One of the most important indicators of ‘‘successful’’ treatment outcome is return to work (Tait, 1999), likely because of the high financial cost of chronic pain in terms of lost occupational productivity and disability payments (Gatchel and Mayer, 2000), as well as the urging of third-party payers (e.g., United States WorkmanÕs Compensation) to reduce these costs. In general, interdisciplinary treatments effectively improve patientsÕ occupational functioning, with success being documented in both rates of return to work (Flor et al., 1992; Cutler et al., 1994) and duration of actual hours worked
1090-3801/$30 Ó 2003 European Federation of Chapters of the International Association for the study of Pain. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ejpain.2003.10.009
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(Hubbard et al., 1996). Given the effectiveness of these treatments, as well as their expense, a number of investigators have attempted to isolate the factors that are associated with increased occupational functioning. Three types of variables primarily have been evaluated: physical, demographic/socioeconomic, and psychosocial. Across studies, physical factors, such as improvements in strength, endurance, or flexibility appear to have little relation to return to work rates following interdisciplinary treatment (Fishbain et al., 1993; Hildebrandt et al., 1997). These findings mirror other studies within chronic pain, which almost uniformly indicate that pre-treatment levels of physical capacity and treatment-mediated changes in physical capacity have minimal discernable effect on treatment outcomes (Burton et al., 1995; McCracken et al., 2002; Vowles and Gross, 2003). The only notable exception to this finding was reported by Matheson et al. (2002), who found that oneÕs ability to lift weight from the floor to waist level had a small, but significant, relation to return to work rates. Conversely, a number of important demographic and socioeconomic factors that are related to treatment outcome have been identified. Individuals who return to work following treatment tend to be younger males (Fishbain et al., 1993). Further, return to work rates are higher among individuals who have been off work for shorter periods of time (Fishbain et al., 1993; Hildebrandt et al., 1997) and who have higher levels of education (Fishbain et al., 1997a). Similarly, Stratton et al. (1996) reported that younger age, greater level of education, and shorter pain duration were important predictors of eventual return to work although their investigation did not include a specific treatment component. Across studies, psychosocial variables appear to have the strongest influence on return to work rates. Lower pre-treatment levels of perceived disability due to pain and lower pain intensity increase the probability that a patient will return to work, while elevated scores on Scale 3 of the Minnesota Multiphasic Personality Inventory, which generally assesses somatic complaints, are a negative influence (Gatchel et al., 1995). With regard to changes in psychosocial variables over the course of treatment that are predictive of outcome, individuals who experience greater reductions in perceived disability and depression are more likely to return to work compared to patients who experience lesser reductions (Hildebrandt et al., 1997). In sum, those who report higher psychosocial distress before treatment or who exhibit lesser changes in distress over the course of treatment tend not to return to work. Previous investigations have identified a number of important factors that individually influence return to work rates. However, given the complexity in determining these rates in individuals with chronic pain, there
is a need for the development of more comprehensive models which take into account the interaction and collective influence of these variables on return to work. Therefore, the present investigation sought to evaluate the relation of a broad range of demographic, physical, and psychosocial factors to post-treatment return to work status in individuals with chronic pain using both univariate and multivariate data analytic strategies. Furthermore, we utilized data collected at the conclusion of a treatment program in order to specifically determine how patientÕs physical and psychosocial functioning at this point in treatment was related to work status.
2. Materials and methods 2.1. Participants Individuals who had completed an interdisciplinary treatment for chronic pain were included in the present analyses. Potential patients for inclusion in the analyses included 183 patients who entered treatment out of 320 total patients assessed over a four-year period (i.e., 1999–2002). For an offer of admission to the treatment program, individuals must have had pain in excess of 90 days, exhibited no psychotic symptomology, and must have had an explicit goal of improving functioning and/ or returning to work. Furthermore, individuals in need of surgical interventions were not admitted to the program. Finally, insurance approval and patient consent were required. Of the patients who accepted an offer of admission into the program, 30 (16.4%) were discharged because of compliance or issues related to non-participation and an additional 15 (8.2%) discontinued treatment for other reasons (e.g., illness, death in the family). Therefore, 138 patients (41% female) completed the treatment program. Treatment completers did not differ from non-completers with regard to age, pain duration, or pre-treatment levels of depression, pain intensity, pain-related fear, pain disability, and demonstrated physical capability based on one-way Analyses of Variance. Further, v2 analyses indicated that gender and marital status classifications were proportional among completers and non-completers. Mean values were used to replace missing data; in all, 13 individuals were missing one point of data, two were missing two points, and two were missing three points. On average, participants were 40.5 years of age (SD ¼ 8:3 years) and married (67.4%; 13.0% single; 17.4% divorced/separated; and 2.2% widowed). Further, mean pain duration was 21.5 months (SD ¼ 17:7 months; range 3–115 months) with low back pain being the most common complaint (68.1%; 15.9% neck; 21.7% upper extremity; and 26.1% lower extremity). In all, 37.7% of the sample endorsed more than one area
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of pain. Since the date of initial injury, none of the participants had successfully returned to work; therefore, for the purposes of the present investigation, duration of injury and time off of work were identical. All patients had sustained work-related injuries that were contributing to their chronic pain problem and were unemployed and receiving WorkmanÕs Compensation benefits at the onset of treatment. With regard to job status, approximately one-half (53%) of the patients who were enrolled in the treatment program had a job available with their prior employer following treatment. Across patients, this availability of a job did not guarantee them a position or a job offer once treatment had concluded. Instead, they had to demonstrate the physical ability to perform the job, as well as a desire to return to it. 2.2. Treatment program Participants were enrolled in an interdisciplinary treatment program based on a sports medicine approach to rehabilitation similar to the one described by Mayer and Gatchel (1988). The program was 4–6 weeks in length; participants attended approximately 6 h/day, 5 days/week. Patients averaged 20.4 days (SD ¼ 4:2 days) in treatment; therefore, the majority of patients completed the 4-week treatment program. Each day, participants attended 3 h of psychoeducational groups and 3 h of physical and occupational therapy. Patients had daily contact with psychology, physical therapy, and occupational therapy staff members, and were seen by a rehabilitation physician at least once per week. In addition to facilitating return to work, the treatment program also sought to increase functional capacity, decrease affective distress, and educate patients about the chronic pain process. 2.3. Measures Prior to completing the treatment program (i.e., 1–2 days), patients completed a number of self-report measures and an assessment of physical capability. Variables selected for inclusion for analysis were based on prior research indicating both the relation of individual variables to return to work rates and to treatment outcome in general, as well as theoretical models of chronic pain distress and disability, as discussed below. 2.3.1. Self-report psychosocial measures 2.3.1.1. Beck Depression Inventory-II. Associations between pain and depression have been found consistently in both acute and chronic pain populations (Fishbain et al., 1997b; Rethelyi et al., 2001). Specifically, depression appears to be associated with more frequent and severe pain reports, in both chronic pain (Krause et al., 1994) and acute pain (Bengtson et al., 1996), and has a
353
negative influence on return to work rates (Gatchel et al., 1995; Hildebrandt et al., 1997). The Beck Depression Inventory-II (BDI-II; Beck et al., 1979) is a 21-item self-report assessment designed to measure clinically relevant cognitive, affective, and vegetative symptoms of depression. Participants rate the degree to which they endorse different depressive symptoms on a 1–4 point Likert-type scale. The BDI-II has demonstrated good psychometric properties (Beck et al., 1988). 2.3.1.2. McGill Pain Questionnaire-Short Form. The total score of the McGill Pain Questionnaire-Short Form (MPQ-SF; Melzack, 1987) was used to assess pain intensity. The psychometric properties of the measure are well established within a chronic pain population, and it has been used widely in both research and clinical settings (Melzack and Katz, 2001). 2.3.1.3. Pain Anxiety Symptoms Scale. Over the past two decades, increasing attention has been paid to the role that pain-related anxiety plays in disability among chronic pain patients. One of the most frequently used measures of pain-related anxiety is the Pain Anxiety Symptoms Scale (PASS; McCracken et al., 1992). A total score, as well as four subscale scores, are derived from the measureÕs 40 items and research supports its psychometric properties and utility within chronic pain (McCracken et al., 1996, 1992; Burns et al., 2000; Strahl et al., 2000). In order to retain statistical power, the present analyses used only the total score of the PASS. 2.3.1.4. Pain Disability Index. The Pain Disability Index (PDI) is a 7-item measure developed to assess the perceived effect that chronic pain has on oneÕs daily functioning (Pollard, 1984). Prior research has indicated that scores on the PDI are reliable and are related to painrelated disability, pain intensity, and general psychological distress (Jerome and Gross, 1991; Tait et al., 1990; Chibnall and Tait, 1994). The amount of perceived disability arising from pain is rated for a number of activities, in areas such as occupation, recreation, social interactions, and self-care, on a 0–10 Likert-type scale, with 0 equivalent to no disability and 10 equal to complete disability. 2.3.2. Physical capacity measures Two measures of physical ability were collected as part of a larger functional capacity examination (FCE). An FCE is designed to assess an individualÕs physical ability to perform vocational activities and is used as a measure of work capability (Snook, 1978). Similar measures have been used in previous experiments and provide an index of actual physical ability (Fishbain et al., 1994; Geisser et al., 2000; McCracken et al., 2002). For the purposes of the present analyses, the amount of
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weight that each participant could lift from the floor to waist level and from waist to shoulder level at posttreatment was utilized. These measures were selected because they appear to be relatively reliable across time and assessor (Smith, 1994; Isernhagen et al., 1999; Gross and Battie, 2002) and, as noted earlier, recent research suggests that at least the floor to waist lift has a significant, albeit moderate, relation to return to work (Matheson et al., 2002). 2.3.3. Return to work For the purposes of the present study, individuals who successfully completed the treatment program were contacted 6 months after treatment completion to ascertain whether they had returned to work since concluding treatment. Patients who reported working on a part-time or full-time basis were coded as having returned to work, as were individuals in job retraining or education programs. These latter two variables were coded as return to work because they represent levels of functioning that mimic in some ways the work environment and elicit work-related behaviors in patients (i.e., patients have to go to some place on a daily basis and keep functioning at relatively consistent levels). Patients who had retired, were on permanent disability, or who were in active job search were coded as not having returned to work. Post-treatment work data could not be ascertained for 11 individuals (8.0%); therefore, additional analyses only included the data of 127 persons. Although a longer follow-up period would have allowed better longitudinal data, this short-term follow-up period was used in order to increase the probability that the actual effect of the treatment program was assessed. Work status after a longer period of time has passed likely is affected by a number of variables (e.g., economic conditions, job availability, other illnesses; Turk, 2002), which are not addressed nor controlled for by the treatment program.
3. Results A total of 90 individuals (70.9%) reported having returned to work within 6 months of treatment completion. Of those who had returned to work, 5.6% (N ¼ 5) reported working part-time, 5.6% (N ¼ 5) were involved in an educational program, and 1.1% (N ¼ 1) reported being involved in job retraining, while the remaining 87.7% (N ¼ 79) reported working full-time. With regard to individuals who reported not working, 45.9% (N ¼ 17) remained in job search and 10.8% (N ¼ 4) were either retired or were classified as permanently disabled by United States Social Security. The remaining 43.2% (N ¼ 16) reported having no plans to return to work in the immediate future. Descriptive data regarding demographic and outcome measures are included in Table 1. Although the efficacy of functional restoration programs was not the focus of the present analyses, it is important to note that over two-thirds of treatment completers returned to work, or were involved in some type of retraining, at the time of follow-up. This is somewhat above the return to work rates reported in the meta-analyses performed by Cutler et al. (1994) and Flor et al. (1992) and is yet another indication regarding the effectiveness of treatments that specifically target a population of individuals who have sustained workrelated injuries. As a preliminary method of investigating the relation of the dependent measures to work status, zero-order correlation coefficients first were calculated. As illustrated in Table 2, individuals reporting higher levels of depression, pain intensity, and pain-related disability at post-treatment were less likely to return to work, as were older persons and those who were able to lift lower amounts of weight from the floor to waist level at the end of treatment. These five variables were retained for a subsequent discriminant analysis. With regard to other indicated correlations, measures of pain, psychosocial
Table 1 Means (SDs) of outcome measures across groups Variable
Group Working
Not working
Combined
Age (years) Education (years) Pain duration (months) BDI-II MPQ-SF PASS PDI Floor to waist lifting (lb) Waist to shoulder lifting (lb)
39.1 11.7 21.0 12.0 16.3 67.9 25.6 58.2 52.6
42.8 11.6 22.9 18.5 20.5 78.2 33.0 51.9 44.3
40.2 11.7 21.6 13.9 17.5 70.9 27.8 56.4 50.2
(7.9) (1.3) (19.5) (8.1) (9.2) (28.1) (11.7) (28.5) (18.5)
(8.6) (0.9) (14.5) (10.3) (8.5) (33.7) (12.2) (25.2) (16.9)
(8.2) (1.2) (18.1) (9.2) (9.2) (30.1) (12.3) (27.6) (18.3)
Note. N ¼ 127. BDI-II, Beck Depression Inventory-II; MPQ-SF, McGill Pain Questionnaire-Short Form; PASS, Pain Anxiety Symptoms Scale; PDI, Pain Disability Index.
– –
Note. , p 6 0:05; , p 6 0:01; , p 6 0:001; N ¼ 127; BDI-II: Beck Depression Inventory-II; MPQ-SF: McGill Pain Questionnaire-Short Form; PASS: Pain Anxiety Symptoms Scale; PDI: Pain Disability Index.
)0.25** )0.51** )0.09 0.004 )0.23** )0.27** )0.07 )0.20* 0.67*** – )0.19* )0.46** 0.14 )0.02 )0.20* )0.27** )0.10 )0.20* – 0.002 )0.09 )0.02 – 0.13
)0.08 )0.08 –
)0.01 0.02 )0.001 )0.02 –
0.06 0.01 )0.19* 0.03 0.54*** –
)0.21* )0.02 )0.03 )0.07 0.54*** 0.43*** –
0.04 )0.14 )0.19* 0.02 0.46*** 0.42*** 0.39*** –
)0.10 )0.21*
10
0.05 )0.06
1
– 1. Work status (1, working; 2, not working) 2. Age (years) 3. Gender (1, male; 2, female) 4. Education (years) 5. Pain duration (months) 6. BDI-II 7. MPQ-SF 8. PASS 9. PDI 10. Floor to waist lifting (lb) 11. Waist to shoulder lifting (lb)
Table 2 Correlations among work status, demographic, and treatment outcome measures
5 4
)0.02
3 2
0.21
6
0.32***
7
0.21*
8
0.16
9
0.27**
11
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355
Table 3 Percentage of correct and incorrectly classifications for post-treatment work status Work status
Working Not working
Predicted work status from initial function n
Working
Not working
61 18
46 (75.4%) 6 (33.3%)
15 (24.6%) 12 (66.7%)
distress, and physical functioning were generally intercorrelated, as is often the case in studies in this area. The final phase of data analysis involved a stepwise discriminant analysis to evaluate the value of patientÕs age and post-treatment levels of depression, pain intensity, pain-related disability, and floor to waist lifting ability to predict participantsÕ work status. A stepwise analysis was utilized rather than a more inclusive fullmodel analysis, in order to identify those measures that were the best predictor(s) of post-treatment work status. The calculated discriminant function was statistically significant, WilksÕ k ¼ 0:72, v2 ð2Þ ¼ 24:57, p 6 0:001. Two variables entered into the equation, depression and participant age; the correlation between these measures and the discriminant function was r ¼ 0:80 and r ¼ 0:51, respectively. The canonical correlation, which measures the relation between the function and variable set, was equal to 0.53, indicating that approximately 28% of the variance in post-treatment work status was accounted for by these two variables. With regard to the actual results of the classification, 73.4% of participants were correctly classified. Table 3 lists specific classification results. In order to cross-validate the classification results, the discriminant analysis was repeated utilizing the U-method, which classifies each individual case in the dataset using a discriminant function derived using all cases other than that case. This method of analyses provides a preliminary validation of classification results that is less susceptible to the inflated accuracy that occurs when the discriminant function derived from a sample is used to classify that same sample (Tabachnick and Fidell, 2001). The cross-validated function correctly classified 72.2% of participants; this function incorrectly classified one more participant than did the original function.
4. Discussion The purpose of the present study was to specifically evaluate a number of factors that have empirical or theoretical relations to return to work in a sample of injured workers experiencing long-term pain. Further, we not only hoped to identify the factor or factors that clinicians and researchers can evaluate at the conclusion of treatment to predict who will return to work and who
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will not, but also to better understand what patient variables would be most important treatment foci to help patients re-establish employment. Within our sample, five factors were significantly correlated with 6-month post-treatment work status and were tested in a subsequent discriminant analysis. Two of these measures, depression and participant age, entered into the equation and accounted for a significant amount of variance. Almost two-thirds of the individuals who completed the treatment program returned to work. Further, psychosocial factors were more strongly related to posttreatment work status than were physical capacity variables, which replicates the findings of a number of investigators (Fishbain et al., 1993; Hildebrandt et al., 1997; McCracken et al., 2002; Vowles and Gross, 2003). Perhaps the most interesting finding of the present investigation was that a general measure of depressive symptomology and psychological distress (the BDI-II) was most highly correlated with the discriminant function predicting post-treatment work status. This result diverges somewhat from previous findings, which have indicated that pain-specific measures, such as fear of pain, fear-avoidance beliefs, perceived disability, and to a lesser extent pain severity, have a greater relation with treatment outcome in individuals with chronic pain (McCracken and Gross, 1998; McCracken et al., 2002; Vowles and Gross, 2003). The present findings add to this body of literature by indicating that depression may have a greater overall impact on some aspects of functioning; in particular, post-treatment job status. This difference in findings likely is accounted for by the fact that successfully participating in gainful employment consists of a number of behaviors and can be affected by a multitude of complex factors, such as economic environment, peer relations, and job availability. Although pain-specific measures likely influence whether or not an individual will succeed at returning to work after a chronic pain treatment program, the effect of these measures may be overshadowed by the effect of depression, which can adversely affect diverse areas such as pain tolerance (Rethelyi et al., 2001; Carter et al., 2002) and physical and social functioning (Kaplan and Sadock, 1998) in the absence of chronic pain. In fact, recent evidence suggests that depression can have significant detrimental effects on work attendance and productivity in individuals without chronic pain. Specifically, Druss et al. (2001) found that workers who were depressed were twice as likely to miss work and seven times as likely to have decreased productivity at work relative to their non-depressed counterparts. Given the wide-ranging effects of depression on functioning in general, and in chronic pain in particular (Robinson and Riley, 1999), it is not surprising an interdisciplinary functional restoration treatment was not as effective with individuals experiencing elevated levels
of depressive symptomology. It is possible that the sample complaining of elevated depression may need additional intervention, or an intervention specific to depression, to achieve similar results. The relevance of age in predicting who will return to work has been indicated before (Fishbain et al., 1993). The present results regarding age serve only to replicate this finding. From a treatment perspective, however, this result is somewhat problematic. From one point of view, it could be argued that these data indicate that older individuals who have been injured at work should not undergo treatment because such interventions appear unlikely to affect this particular variable. This argument, however, is flawed because we do not yet know why older individuals are less likely to return to work and it discounts the benefits of treatment on depressive symptoms (and other psychological factors) irrespective of work status following treatment. It may be that older patients prefer to retire, have poorer access to jobs, are less likely to be hired, or are less likely to be selected by employees to be retrained. Although any of these reasons are plausible, we are unaware of any studies investigating which, if any, are empirically verifiable. In addition to patient variables and characteristics of employment, there may be treatment variables that need to be adjusted to better serve older patients in returning to work following treatment. In all, the calculated discriminant function indicated that patientÕs post-treatment level of depression and age accounted for approximately 28% of the variability in post-treatment job status. Although this amount of variance leaves over two-thirds of the variance unaccounted for, the present findings are nonetheless important because level of depression is something that can be effectively treated. The other important variables in determining post-treatment work status likely consist of many job-related and environmental factors, such as job availability, rates of unemployment, local economy, and job satisfaction, which are not addressed by interdisciplinary treatment programs. The same logic obviously applies to demographic variables (e.g., age, gender) as well. Therefore, it is important to identify those variables that affect outcomes that can be effectively addressed in treatment. Level of post-treatment depression represents one of these factors, and there are effective treatments available. Within interdisciplinary functional restoration treatments, patients engage in many new, ‘‘healthy’’ behaviors, such as increased physical activity, social contact, work readiness, and recreational activities that may be incompatible with depressive behaviors, as evidenced by literature concerning depression (Lejuez et al., 2001). Given that selfreported depression had the greatest relation with work status following treatment, increasing ‘‘healthy’’ behaviors in treatment programs for chronic pain may be of the utmost importance.
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With regard to limitations, the relatively small number of participants included in the present study leads to a reduction in the power of the analyses and decreases the possibility of generalization to other individuals in treatment for chronic pain. The collection of data from a larger pool of participants would allow these issues to be addressed. Second, despite the initial inclusion of overt measures, only self-report measures were included in the final discriminant analysis leading to the possibility of many types of well-documented errors associated with this type of data. Perhaps further investigations could include additional measures of physical capacity, or other overt measures of behavior, to determine the utility of such variables. We also did not collect data regarding the types of jobs that patients return to following the program, nor the physical demand of those jobs. This does not allow us to assess for differences with regard to the physical demand of the post-treatment job. Finally, the results are limited by the statistical methods used. The model of post-treatment functioning for individuals with chronic pain is complex; therefore, the use of more sophisticated data analytic techniques, which allow the evaluation of multidirectional models (e.g., path analysis and structural equation modeling), may be of significant utility in elucidating the exact mediators of chronic pain treatment outcome. A few additional comments regarding the present study are necessary. First, these data generally support the efficacy of this type of treatment as a means of improving the probability of return to work. This sample, however, was selected based on their desire to improve functional ability; therefore, these data do not necessarily generalize to individuals with chronic pain who do not espouse such goals, nor to individuals who did not complete treatment. Nonetheless, given the accumulating literature supporting such interventions (see Turk, 2002 for a review), it is reasonable to conclude that these types of treatment are effective for a sizable proportion of individuals with chronic pain. The second issue pertains to the nature of the WorkmanÕs Compensation system in the United States. Within this system, there are definite contingencies on patients to return to work, which include the fact that they receive only a percentage of their previous wage and have to continue to provide documentation of their disability over time in order to continue to receive benefits. It is likely these contingencies, which are inherent in the system, aided the outcome of the present study. It is not possible to determine the extent to which they helped and it should be noted that this was a treatment refractory sample who were, on average, almost 2 years post-injury and who had not returned to work on their own or as a result of previous interventions. Therefore, it can be argued that the treatment program acted as a catalyst, or at very least helped
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motivate patients, to return to work. In other socioeconomic systems, there may be no contingencies for patients to return to work or alternative contingencies that exert stronger influence on patientÕs behavior to do other things (e.g., remain on disability). From a behavioral perspective, the lack of contingencies and/or stronger, more influential contingencies decreases the probability that patients will return to work. We have analyses that are currently underway from a similar treatment program in the United Kingdom which may allow some of these issues to be addressed. In sum, the findings of the present investigation add to the emerging complex model of treatment outcome for individuals with chronic pain. As indicated in previous studies, psychosocial measures were more predictive of treatment outcome than physical capacity measures. Furthermore, although previous investigations have found that pain-specific variables such as pain-related anxiety and fear-avoidance beliefs significantly predict other measures of distress and disability (e.g., pain severity, depression, and physical capacity), the current study extends these results to show that general distress, as measured by the BDI-II, significantly predicts post-treatment work status. That this general measure of distress was most associated with posttreatment work status underscores the effects that depression can have on oneÕs functioning and the clinical importance of addressing this area in treatment programs for chronic pain.
Acknowledgements The authors thank the entire staff at PSIMED and Oasis Occupational Rehabilitation and Pain Management for their support and assistance in the collection of data for this project. Thanks also to Stanley Cohen, Ph.D., for comments on an earlier draft of this manuscript.
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