Chronic pain, work performance and litigation

Pain 103 (2003) 41–47 www.elsevier.com/locate/pain

Chronic pain, work performance and litigation Fiona M. Blyth a,*, Lyn M. March b, Michael K. Nicholas a, Michael J. Cousins a a

University of Sydney Pain Management and Research Centre, Royal North Shore Hospital, St Leonards, NSW 2065, Australia b University of Sydney, Department of Rheumatology, Royal North Shore Hospital, St Leonards, NSW 2065, Australia Received 27 May 2002; accepted 23 September 2002

Abstract The overall population impact of chronic pain on work performance has been underestimated as it has often been described in terms of work-related absence, excluding more subtle effects that chronic pain may have on the ability to work effectively. Additionally, most studies have focussed on occupational and/or patient cohorts and treatment seeking, rather than sampling from the general population. We undertook a population-based random digit dialling computer-assisted telephone survey with participants randomly selected within households in order to measure the impact of chronic pain on work performance. In addition, we measured the association between pain-related disability and litigation. The study took place in Northern Sydney Health Area, a geographically defined urban area of New South Wales, Australia, and included 484 adults aged 18 or over with chronic pain. The response rate was 73.4%. Working with pain was more common (on an average 83.8 days in 6 months) than lost work days due to pain (4.5 days) among chronic pain participants in full-time or part-time employment. When both lost work days and reduced-effectiveness work days were summed, an average of 16.4 lost work day equivalents occurred in a 6month period, approximately three times the average number of lost work days. In multiple logistic regression modelling with pain-related disability as the dependent variable, past or present pain-related litigation had the strongest association (odds ratio (OR) ¼ 3.59, P ¼ 0:001). In conclusion, chronic pain had a larger impact on work performance than has previously been recognised, related to reduced performance while working with pain. A significant proportion were able to work effectively with pain, suggesting that complete relief of pain may not be an essential therapeutic target. Litigation (principally work-related) for chronic pain was strongly associated with higher levels of painrelated disability, even after taking into account other factors associated with poor functional outcomes. q 2002 International Association for the Study of Pain. Published by Elsevier Science B.V. All rights reserved. Keywords: Chronic pain; Epidemiology; Survey; Random digit dialling methods; Work performance; Litigation

1. Introduction New South Wales (NSW), Australia’s most populous state, has a compensation system for work- and transportrelated accidents which relies on tort law; in other words, it is adversarial in nature. The adversarial process has been identified as inappropriate for treatment of pain problems (Hadler, 1996; Fordyce, 1995). In NSW, as seen in industrialised countries, there has been a substantial rise in the assignment of permanent disability from work-related injuries (Frymoyer and Cats-Baril, 1991; Rosen, 1994; Grellman, 1997). Back injuries (overwhelmingly with the diagnosis of sprains and strains) accounted for a significant proportion of injuries. Awards for pain and suffering have been identified as one of the key factors increasing worker’s compensation costs (Grellman, 1997). Therefore, the issue * Corresponding author. Tel.: 1 0061-2-9926-6775; fax: 10061-2-9926 6780. E-mail address: [email protected] (F.M. Blyth).

of pain and litigation has emerged as an important issue in NSW. Studies looking at the association between litigation and poor pain outcomes have largely been undertaken in selected populations (such as those seeking treatment), where referral patterns, litigation systems and factors influencing care-seeking may have an effect on this association. These effects would be minimised in a community-based study, and have the additional benefit of providing a meaningful comparison group (a representative group of community-dwelling subjects with chronic pain). In addition, few studies in this area have considered the effect of other factors known to be associated with pain-related disability (such as distress). In addition, it is possible that the impact of chronic pain on work has been underestimated as it has often been described in terms of work-related absence, excluding more subtle effects that chronic pain may have on the ability to work effectively. However, most studies have dealt exclusively with occupational and/or patient cohorts, so that the

0304-3959/02/$30.00 q 2002 International Association for the Study of Pain. Published by Elsevier Science B.V. All rights reserved. doi:10.1016/S0 304-3959(02)00 380-9

42

F.M. Blyth et al. / Pain 103 (2003) 41–47

overall population impact of this problem has not been well described. The aim of this paper is to examine (i) the effect of chronic pain on ability to work full-time or part-time and (ii) the association between pain-related disability and litigation in a population-based study of chronic pain, the Northern Sydney Area (NSA) Pain Study.

2. Methods Data were collected by computer assisted telephone interview (CATI) techniques using random digit dialling methods within the NSA, an urban geographical area with a base population exceeding 700,000 (Australian Bureau of Statistics, 1997). Once contact was made with a household, participants were chosen by randomly sampling from eligible household members (18 years of age or more, and speaking English as their primary language); after the interviewer obtained information about the number of eligible household members from the initial household contact, one eligible household member was selected randomly by the CATI programme. The sampling method used was based on a previous study of a state-wide population (Blyth et al., 2001). Data collection occurred between July and September, 1998. Chronic pain was defined as pain experienced every day for 3 months or more in the 6 months prior to interview. This definition is consistent with other studies (e.g. Blyth et al., 2001; Von Korff et al., 1992; Purves et al., 1998; Carey et al., 1999) and with the International Association for the Study of Pain definition of chronicity (IASP, 1986). Pain severity was measured using the Chronic Pain Grade (CPG) (Von Korff et al., 1992). The CPG questionnaire contains three items on pain intensity (0–10 ratings of current, worst and average pain over a 6-month period); and four items on pain-related disability (number of days kept from usual activities because of pain, a 0–10 rating of interference with daily activity, a 0–10 rating of change in ability to take part in recreational, social and family activities, and a 0–10 rating of change in ability to work, all over a 6-month period). Responses were scored to produce four grades of pain severity. They are I, low disability–low intensity pain; II, low disability–high intensity pain; III, high disability–moderately limiting pain; and IV, high disability–severely limiting pain. Psychological distress was measured using a ten-item questionnaire (K10), which included items on the level of anxiety and depressive symptoms in the preceding 4 weeks (Kessler and Mroczek, 1994). Questionnaire items covered the range from minor symptoms to high levels of distress, making it useful for use in population surveys. For example, respondents were asked, ‘In the last 4 weeks, how often did you feel that everything was an effort?’ For each item, there is a five-point adjective scale related to the amount of time during the preceding 4 weeks that the respondent experi-

enced the particular problem (from ‘none of the time’ to ‘all of the time’). Raw scores ranging between 0 and 50 were converted to a T-score with a mean of 50 and a standard deviation of 10. Scores of 60 or more (representing one standard deviation above the mean) have been found to correspond to high levels of psychological distress using other established measures in the NSW population (NSW Health Department, 1999). The measure of work impact was adapted from a pain impact measure used in population studies of headache (Stewart et al., 1998a). Briefly, an estimate of days of working with reduced effectiveness could be obtained from multiplying the number of days worked with pain by the percent reduction in effectiveness on days worked with pain. For example, 2 days worked with pain with a 50% reduction in effectiveness would result in 1 reduced-effectiveness work day. The NSA study included two questions about pain-related litigation. The first identified respondents whose pain problem had been the subject of a claim for damages or a legal case. The second identified the system involved (worker’s compensation, third party accident compensation or other). Owing to the sensitive nature of these questions, they were kept deliberately brief. However, only five participants refused to answer these questions. 2.1. Statistical analysis Adjustment was made for differences between the age/ sex structure of the survey and the NSA population, as well as for household size, by weighting. Differences between proportions were assessed using a two-proportion test with weighted standard errors. After checking for conformity with a normal distribution, differences between means from independent samples were assessed using a twosample t-test with weighted standard errors. Trends in proportions by CPG were tested using the chi-squared test for trend. Logistic regression modelling was done using Stata Release 6.0 (StataCorp, 1999), and probability sampling weights were used. To create a two-level dependent variable for regression analysis, CPG scores were dichotomised with grades I and II grouped into a low disability group, and grades III and IV grouped into a high disability group, a grouping also used by the originators of the CPG (Von Korff et al., 1992). Independent variables were chosen based on previous studies and demonstration of a significant association in 2 £ r Table analysis (P # 0:1), on the basis of an hypothesised relationship with pain-related disability. Age and sex were included in all models because of the fundamental biological significance of these variables. Reduced (i.e. parsimonious models) were produced by a process of backward elimination of independent variables. At each stage, the effect of dropping out an independent variable was assessed using the likelihood ratio test (G statistic) at a significance level of P ¼ 0:05. ORs, beta coef-

F.M. Blyth et al. / Pain 103 (2003) 41–47

43

Table 1 Demographic and employment characteristics of chronic pain participants

Table 3 Rating of reduced ability to work due to pain

Demographic characteristics

N

Rating a

N

%

Female gender Mean age (years) a Australian-born Language other than English spoken at home

293 56.7 (51.7–61.7) 468 49.8 years (48.0–51.6) 335 70.9 (66.5–75.4) 44 10.2 (7.0–13.3)

0 1–5 6–10 Do not know

103 135 13 10

38.7 53.3 4.9 3.0

Employment status b Employed full-time Employed part-time Unemployed Home duties Student Retired Unable to work/health reasons Chronic pain work-related a b

% (95% confidence limit, CL)

a Rating from 0 (no reduction) to 10 (unable to do at all); converted to percentages to estimate reduced effectiveness.

189 72 8 64 14 114 11

44.0 (39.1–49.0) 15.6 (12.0–19.3) 2.0 (0.6–3.4) 12.8 (9.7–15.9) 2.7 (0.6–4.4) 20.5 (16.7–24.3) 2.3 (0.8–3.9)

40

18.2 (14.6–22.6)

n ¼ 8 missing data. n ¼ 2 missing data.

ficients and standard errors were inspected at each stage to check for possible confounding or effect modification. Goodness-of-fit and regression diagnostics for the reduced model were assessed using the methods described by Hosmer and Lemeshow (1989). Model weighting was applied to the reduced models using Stata’s Svylogit procedure. Ethics approval was obtained from the NSA Ethics Committee. 3. Results The response rate was 73.4%. 3.1. Prevalence The crude prevalence of chronic pain in the NSA Study was 19.9% for males and 24.1% for females, with an overall prevalence of 22.1%; 27.0% of chronic pain participants were in the high disability CPG categories III and IV (data not shown). Table 1 shows that within the group with chronic pain, there was a slight excess of females overall (56.7%). Table 2 Days in last 6 months kept from work and working with pain Number of days Kept from working in last 6 months

0 1–6 7–14 15–30 . 30 Do not know

3.2. Work Among the chronic pain pariticipants, 44.0% were in fulltime employment, with a further 15.6% in part-time employment (Table 1). Chronic pain participants who reported that they were working full-time or part-time were asked questions about the impact of pain on their work (n ¼ 261) (data not shown). Overall, 28.6% reported that their work was restricted by their pain problem. Chronic pain participants in full-time or part-time work were also asked how many days they had been kept from work by their pain problem in the 6 months prior to interview (Table 2). While most (66.6%) reported none or few days kept from work, more than 10% reported a week or more of being kept from work by their pain in the previous 6 months. A small proportion (5.5%) reported more than 30 days in the previous 6 months when they had been kept from work by their pain. Chronic pain participants in full-time or part-time work commonly reported working in the presence of their pain problem, with 68.5% reporting more than 30 days of this type in the previous 6 months. Similar proportion of males and females fell into this category. Most participants (60% males and 54% females) reported some degree of reduction in their work effectiveness due to their pain (Table 3). Interestingly, 38.9% of those who had worked with pain stated that they experienced no reduction in their ability to perform their work. 3.3. Lost work day equivalents Table 4 shows that the phenomenon of working with pain was very common (on an average 83.8 days in 6 months) compared with lost work days (4.5 days) among chronic

Days of working with pain

Table 4 Distributional characteristics of lost work days and lost work day equivalents

N

Work impact variables

N

% (95% CL)

173 47 12 10 16 3

66.6 (60.4–72.8) 13 18.9 (13.6–24.2) 16 4.2 (1.8–6.7) 10 2.9 (1.0–4.8) 33 5.5 (2.8–8.3) 177 0.9 (0.0–2.2) 12

% (95% CL) 5.1 (2.1–8.0) 6.7 (3.3–10.1) 3.2 (1.2–5.3) 12.8 (8.4–17.2) 68.5 (62.4–74.6) 3.7 (1.2–6.2)

Work days with pain Lost work days Percent reduced effectiveness Lost work day equivalents

Distributional characteristics Mean (sd)

Median

83.8 (55.0) days 4.5 (13.2) days 14.2% (20.5)% 16.4 (28.4) days

80 days 0 days 3% 3.3 days

44

F.M. Blyth et al. / Pain 103 (2003) 41–47

pain participants in full-time or part-time employment. These participants reported an average reduction in effectiveness of 14.2% on days worked with pain. When both lost work days and reduced-effectiveness work days were summed, an average of 16.4 lost work day equivalents occurred in a 6-month period, more than three times the average number of lost work days. The distributional characteristics of the lost work day equivalents variable show that a small proportion of participants had a high number of lost work day equivalents. Overall, about one-third of those in full-time or part-time work reported 1 or more days lost from work because of pain in the 6 months prior to interview (32.4%), and nearly all (96.8%) reported 1 or more days of working with pain (Table 5). More than half of those who worked with pain (59.6%) reported that pain reduced their work effectiveness. Even amongst those reporting no lost work days, almost half (45.7%) reported lost work day equivalents. Similar patterns were seen for both males and females.

differed markedly between the two groups; those with a legal claim were significantly more likely to report multiple pain sites, have an injury as the cause of their pain, and require help at home with activities of daily living. Almost twice as many in this group were in CPG III or IV. They were significantly more likely to report having a preceding cause for their pain. There were also non-significant increases in the proportions in the legal claim group who expected their pain problem to get worse in the future and who reported pain-related interference with sleep. A smaller proportion of this group had pain duration of 12 months or more. The legal claim group was almost twice as likely to be using oral narcotic drugs and multiple medications for pain. There were striking differences between the groups on several measures of health services usage. Significantly more of the legal claim group reported multiple visits to doctors or other health professionals, seeing multiple doctor types, having made a recent GP visit, and having pain-related investigations and hospital admissions.

3.4. Litigation

3.6. Logistic regression modelling with pain disability as the dependent variable

All chronic pain participants were asked whether their pain problem had been the subject of a claim for damages or a legal case. Overall, 8.7% responded affirmatively to this question (data not shown). Males were twice as likely to report involvement in litigation compared with females (12.0% versus 6.2%). The most common type of legal claim reported was a workers compensation claim (51.4%), followed by a third party accident compensation claim (24.2%). Males were more likely to report a workers compensation claim (55.0%) compared with females (46.1%). In contrast, females were more likely to be involved in third party accident compensation. 3.5. Comparison of legal claimants with other chronic pain participants Table 6 compares chronic pain participants who had a legal claim related to their pain problem to those with no legal claim. Legal claimants were more likely to be males and tended to be younger. Notably, the two groups had similar full-time employment rates. There were more in the legal claimants group who were distressed or reporting poor/fair self-rated health. Characteristics of pain problems Table 5 Other characteristics of lost work days and lost work day equivalents, chronic pain participants Work impact variables

N*

% (95% CL)

1 or more days of lost work 1 or more days of working with pain Those with no lost work days who have lost work day equivalents Working with reduced effectiveness

78 234 72

32.4 (26.0–38.8) 96.8 (94.3–99.4) 45.7 (37.3–54.1)

142

59.6 (52.8–66.4)

* N ¼ 241 participants with no missing data for variable.

The objective of this phase of modelling was to examine the relationship between litigation and pain-related disability in the NSA chronic pain subgroup, using the 417 cases with complete data on explanatory and outcome variables. Table 7 shows the ORs for variables in the reduced model with pain-related disability as the dependent variable. Past or present pain-related litigation had the strongest association (OR ¼ 3:59, P ¼ 0:001). Participants with pain-related disability were almost twice as likely to report having psychological distress, poor self-rated health, or multiple pain sites compared with those who had low pain-related disability. 4. Discussion This study, with its use of a random sample of community-dwelling chronic pain participants and good response rate, differs from many previous studies, which have largely been based on those seeking treatment, or on certain occupational groups. The measure of work impact employed in this study had been developed to estimate the impact of chronic pain due to headaches. It is conceptually based on the CPG (Von Korff et al., 1994), has been validated against prospectively collected diary data with a 3-month recall period (Stewart et al., 1999), and shown to be reliable (Stewart et al., 1998b). We acknowledge that the data presented here are based on self-report measures. In addition, the data are cross-sectional, and the direction of associations found between variables cannot be ascertained. The results show that most participants with chronic pain reported working despite their pain. However, more than half reported some reduction in work effectiveness due to pain. This suggests that measures of work absence per se do

F.M. Blyth et al. / Pain 103 (2003) 41–47

45

Table 6 Comparisons of demographic and other characteristics by ligation status, chronic pain participants Demographic and other characteristics

Pain-related litigation No (n ¼ 383)

Yes (n ¼ 34)

Na

%

Na

%

140

40.8

20

58.3

0.015

Age group (years) 18–29 30–39 40–49 50–59 60–69 70 1

50 53 75 76 51 78

16.4 12.7 20.6 23.4 12.8 14.0

6 10 9 3 4 2

18.1 27.8 26.4 9.7 12.5 5.6

0.206 0.017 0.122 0.006 0.239 0.011

Employed full-time

161

46.2

17

48.6

0.199

University or other post-school qualification

191

53.3

19

58.3

0.147

61 90 64

15.9 22.1 16.8

7 9 9

20.8 27.8 29.2

0.133 0.126 0.039

Pain characteristics Pain-related disability (CPG III or IV) Three or more pain sites Pain duration 12 months or more

104 105 106

24.7 23.9 29.6

18 15 7

51.4 50.0 20.8

0.001 0.001 0.066

Injury as cause of pain

145

40.7

27

76.4

, 0.001

88

21.1

17

50.0

, 0.001

Oral medication Narcotic or combination narcotic analgesics Two or more medications

52 126

12.5 32.2

12 20

34.7 61.1

0.003 , 0.001

Health services use Four or more doctor visits for pain in last 6 months b Six or more other health professional visits for pain in last 6 months b Seen three or more types of doctors for pain in last 6 months GP visit in last 2 weeks for pain Radiological investigations for pain in last 6 months Hospital admission for pain in last 6 months Sleep problems due to pain

62 106 28 56 117 27 283

14.2 25.4 6.6 12.2 30.7 7.0 74.8

15 14 7 8 17 7 29

44.4 43.1 18.1 23.6 52.8 22.2 87.5

, 0.001 0.015 0.020 0.039 0.004 0.013 0.010

Male

Psychological factors Psychological distress (K10 score of 60 or more) Poor/fair self-rated health Expects pain problem to get worse

Uses formal or informal help at home due to pain

a b

N ¼ 417 respondents with no missing data for all variables. Represents upper quartile of visits for chronic pain participants.

not capture the full impact of pain on work. In this respect, the lost work day equivalents measure reveals a more complete picture. About two-thirds of those in full-time or Table 7 Adjusted ORs for predictors of pain-related disability a Variable

Adjusted OR (95% CL)

P-value

Pain-related litigation Psychological distress Poor/fair self-rated health Three or more pain sites Female gender Age

3.59 (1.65–7.83) 1.96 (1.10–3.51) 1.72 (1.03–2.87) 1.70 (1.04–2.78) 1.61 (0.98–2.63) 1.01 (0.99–1.02)

0.001 0.023 0.039 0.033 0.056 0.096

a

P-value

CPG III or IV (high disability) versus CPG I or II (low disability).

part-time work reported 1 or more days off work due to pain in a 6-month period. When the impact of working with pain that reduced effectiveness of work performance was assessed, lost productivity was more than three times that obtained by asking about days missed from work (note that this measure does not include estimates of part-days lost or worked with pain). This finding is consistent with other studies, using different measures of work impact, that have shown that pain is a threat to work capacity (e.g. Crook et al., 1984; Gureje et al., 1998; Birse and Lander, 1998; Elliott et al., 1999). The mean values for lost work days and lost work day equivalents were skewed to the right of median values, suggesting that a small group of participants accounted for a large proportion of these values. This effect has

46

F.M. Blyth et al. / Pain 103 (2003) 41–47

also been found using the same measure in a populationbased sample of migraine sufferers (Von Korff et al., 1998). The average values for lost work days and lost work day equivalents were approximately three times higher than those reported for migraineurs, which is not surprising given the episodic nature of migraine and the shorter recall period in that study. The study also identified a substantial group of participants who reported doing activities with pain while experiencing no reduction in their ability to perform their work. This suggests that complete removal of pain is not always required for effective functioning, which is consistent with existing guidelines for the management of acute low back pain (e.g. Waddell and Burton, 1999). Further investigation of this particular subgroup could provide insights into the provision of health services and supports for those working with chronic pain. Factors such as job flexibility and employer response to injury are already identified as important in this area (e.g. Sanderson et al., 1995). Already promising results have been reported by some Swedish studies, which have indicated that cognitive–behavioural interventions targeted at improving adjustment to persisting low back pain while the injured workers still have a job can greatly reduce lost work days and health service utilisation (Linton et al., 1989; Linton and Ryberg, 2001). 4.1. Pain-related litigation Litigants did more poorly than non-litigants did across a wide range of pain-related variables, including pain-related disability, medication use, and health services use. The 6month recall period used was long enough to exclude the majority of those injured who return to normal activity within 3 months of injury, whilst identifying those with symptoms of 3 months or more duration. It is this latter group who, in occupational settings, are at greatest risk of long-term disability (Spitzer et al., 1987). It was beyond the scope of the study to collect data on work place variables or the severity of preceding injury, and these have not been taken into account in the modelling. Therefore, it was not possible to look at the relationship of work place variables or injury severity to pain-related disability and litigation. It is possible that the prevalence estimate of 8.7% for legal claims related to pain problems is an underestimate for two reasons. Firstly, study participants tended to be elderly (and not in the age group at risk of a work-related pain problem); and, secondly, participants may have been reluctant to reveal information about litigation. In addition, litigants were treated as a single group in the modelling, owing to the small number in this group. Therefore, the effect of current versus past litigation and type of litigation were not examined. Current employment status (full-time employment versus other) was included in the full model, but did not emerge as a predictor in the final reduced model. However, previous studies (e.g. Tait et al., 1990; Mendelson, 1992) have suggested there may be an interaction

between employment status, the presence of compensation and health outcomes. The findings from the study are consistent with those of the meta-analysis of 32 studies of the association between compensation status (any type) and chronic pain (Rohling et al., 1995). This meta-analysis found no difference between the compensation and non-compensation group regarding unemployment status or severity of physical injury. However, receiving financial compensation was associated with poorer outcomes and reduced treatment efficacy. There is evidence from patient-based studies that involvement in litigation is associated with poorer outcomes (e.g. Coste et al., 1994; Law Commission, 1995; Fraser, 1996; Dionne et al., 1999). However, few studies have been able to adjust for the effects of other factors besides litigation status in their analysis of outcomes. This study identified participants who had been or were involved in pain-related litigation as being a group having higher levels of pain-related disability. Unlike many studies in this field, an association between litigation and poor chronic pain outcome was demonstrated in a randomly selected population-based sample (rather than an occupational or a clinical one) and adjusted for other factors associated with having pain-related disability (age, gender, selfrated health, psychological distress and multiple pain sites). These results are striking, and suggest that there is a need to establish to what extent the compensation process per se contributes to these outcomes. The finding that litigants were not only more disabled, but also utilised health services, home help, and medication more than non-litigants is noteworthy and suggests the possibility of an interaction between having a compensation claim and the response of the health system contributing to disability. In this context it is worth noting that a number of authors have identified a relationship between the ways in which those with ongoing pain are responded to and their disability outcomes (e.g. Cohen et al., 2000; Loeser, 1996). These findings should inform a wider review of the interaction between the health system and personal injury/worker’s compensation litigation systems, which are legitimate areas of public health concern.

Acknowledgements We are grateful to Dr Michael Von Korff for his helpful suggestions in the planning stages of this study. This study is part of a series funded by a programme grant to the Pain Management and Research Centre as an NHMRC Centre of Clinical Excellence in Hospital Based Research. Dr Blyth was funded by a National Health and Medical Research Council (NHMRC) postgraduate training scholarship. This study was also financially supported by research grants from the Joint Coal Board, Workcover Australia, Northern Sydney Area Health Service and the Centre for Anaesthesia and Pain Management Research Ltd. We thank Marina Van Leeuwen for help editing tables.

F.M. Blyth et al. / Pain 103 (2003) 41–47

References Australian Bureau of Statistics. 1997 Estimated resident population [electronic], Health Outcomes Statistical Toolkit (HOIST), Epidemiology and Surveillance Branch, NSW Health Department; 1997. Birse TM, Lander J. Prevalence of chronic pain. Can J Public Health 1998;89(2):129–131. Blyth FM, March LM, Brnabic AJM, Jorm LR, Williamson M, Cousins MJ. Chronic pain in Australia: a prevalence study. Pain 2001;89(2–3):127– 134. Carey TS, Garrett JM, Jackman A, Hadler N. Recurrence and care seeking after acute back pain: results of a long-term follow-up study. North Carolina back pain project. Med Care 1999;37(2):157–164. Cohen M, Nicholas MK, Bland A. Medical assessment and management of work-related low back and neck/arm pain. Occup Health Saf Aust NZ 2000;16(4):307–317. Coste J, Delecoeuillerie G, Cohen de Lara A, Le Parc JM, Paolaggi JB. Clinical course and prognostic factors in acute low back pain: an inception cohort study in primary care practice. Br Med J 1994;308:577–580. Crook J, Rideout E, Browne G. The prevalence of pain complaints in a general population. Pain 1984;18:299–314. Dionne CE, Von Korff M, Koepsell TD, Deyo RA, Barlow WE, Checkoway H. A comparison of pain, functional limitations, and work status indices as outcome measures in back pain research. Spine 1999;24(22):2339–2345. Elliott AM, Smith BH, Penny KI, Smith WC, Chambers WA, The epidemiology of chronic pain in the community. The Lancet 1999;354:1248– 1252. Fordyce WE, editor. Backpain in the workplace. Management of disability in nonspecific conditions Seattle: IASP Press, 1995. Fraser RD. Compensation and recovery from injury. Med J Aust 1996;165(2):80–82. Frymoyer J, Cats-Baril W. An overview of the incidences and costs of low back pain. Orthop Clin. North Am 1991;22:253–271. Grellman RJ. Inquiry into workers’ compensation system in NSW (final report). Dept. of the NSW Attorney-General and Minister for Industrial Relations; 1997. Gureje O, Von Korff M, Simon GE, Gator R. Persistent pain and wellbeing: a World Health Organisation study in primary care. J Am Med Assoc 1998;280(2):147–151. Hadler NM. If you have to prove you are ill, you can’t get well: the object lesson of fibromyalgia. Spine 1996;21:2397–2400. Hosmer DW, Lemeshow S. Applied logistic regression. USA: Wiley, 1989. IASP. Classification of chronic pain. Description of chronic pain syndromes and definitions of pain terms. Pain 1986(Suppl 3). Kessler R, Mroczek D. Final versions of our non-specific psychological distress scale. The University of Michigan; March 10, 1994 [open research memorandum]; 1994. Law Commission Consultation Paper No. 140. Damages for personal injury: non-pecuniary loss. London: HMSO; 1995. Linton SJ, Ryberg M. A cognitive-behavioral group intervention as prevention for persistent neck and back pain in a non-patient population: a randomized trial. Pain 2001;90:83–90.

47

Linton SJ, Bradley LA, Jensen I, Spangfort E, Sundell L. The secondary prevention of low back pain: a controlled study with follow-up. Pain 1989;29:197–207. Loeser JD. Mitigating the dangers of pursuing cure. In: Cohen MJM, Campbell JN, editors. Pain treatment centres at a crossroads: a practical and conceptual reappraisal, progress in pain research and management, Vol. 7. Seattle: IASP Press, 1996. pp. 101–108. Mendelson G. Chronic pain and compensation. In: Tyrer SP, editor. Psychology, psychiatry and chronic pain, Oxford: Butterworth Heinemann, 1992. pp. 68–78. NSW Health Department. Epidemiology and Surveillance Branch. NSW Health Survey 1997 Electronic Report; 1997. Available from: http:// 10.192.128.9/public-health/nswhs/index.htm. Purves AM, Penny KI, Munro C, Smith BH, Grimshaw J, Wilson B, Smith WC, Chambers WA. Pain Clinic 1998;10(3):139–147. Rohling ML, Binder LM, Langhinrichsen-Rohling J. Money matters: a meta-analytic review of the association between financial compensation and the experience and treatment of chronic pain. Health Psychol 1995;14(6):537–547. Rosen M. Report of a clinical standards advisory group committee on back pain for UK health ministers, . London: HMSO, 1994. Sanderson PL, Todd BD, Holt GR, Getty CJ. Compensation, work status, and disability in low back pain patients. Spine 1995;20:554–556. Spitzer WO, LeBlanc FE, DuPuis M. Scientific approach to the assessment and management of activity-related spinal disorders: a monograph for clinicians. Report of the Task Force on Spinal Disorders. Spine 1987;12(Suppl 7):S9–S59. STATA Statistical Software: Release 6.0. College Station, Texas: Stata Corporation; 1999. Stewart WF, Lipton RB, Simon D, Von Korff M, Liberman J. Reliability of an illness severity measure for headache in a population sample of migraine sufferers. Cephalalgia 1998a;18(1):44–51. Stewart WF, Lipton RB, Simon D, Von Korff M, Liberman J. Reliability of an illness severity measure for headache in a population sample of migraine sufferers. Cephalalgia 1998b;18(1):44–51. Stewart WF, Lipton RB, Simon D, Liberman J, Von Korff M. Validity of an illness severity measure for headache in a population sample of migraine sufferers. Pain 1999;79(2-3):291–301. Tait R, Chibnall JT, Richardson WD. Litigation and employment status: effects on patients with chronic pain. Pain 1990;43:37–46. Von Korff M, Ormel J, Keefe F, Dworkin SF. Grading the severity of chronic pain. Pain 1992;50:133–149. Von Korff M, Stewart WF, Lipton RB. Assessing headache severity. New directions. Neurology 1994;44(6 Suppl 4):S40–S46. Von Korff M, Stewart WF, Simon DJ, Lipton RB. Migraine and reduced work performance: a population-based diary study. Neurology 1998;50(6):1741–1745. Waddell G, Burton K. Evidence review. In: Carter JT, Birrell LN, editors. Occupational health guidelines for the management of low back pain at work—principal recommendations, London: Faculty of Occupational Medicine, 1999. p. 2000.