COST-EFFECTIVENESS STUDIES OF MEDICAL AND CHIROPRACTIC CARE FOR OCCUPATIONAL LOW BACK PAIN. A CRITICAL REVIEW OF THE LITERATURE
 
   

Cost-effectiveness Studies of Medical and Chiropractic Care for
Occupational Low Back Pain. A Critical Review of the Literature

This section was compiled by Frank M. Painter, D.C.
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  Frankp@chiro.org
 
   

FROM:   Spine J. 2001 (Mar);   1 (2):   138–147 ~ FULL TEXT

Marjorie L. Baldwin, PhD, Pierre Côté, DC, MSc, John W. Frank, MD, MSc, William G. Johnson, PhD

Department of Economics,
East Carolina University,
A433 Brewster, Greenville, NC 27834, USA


BACKGROUND CONTEXT:   Back pain is the single most costly work-related injury. Chiropractors and physicians are the main primary care providers for occupational low back pain (OLBP), but there is no consensus regarding the relative cost-effectiveness of these two modes of care.

PURPOSE:   To critically appraise and synthesize recent literature on the cost-effectiveness of medical and chiropractic care for OLBP, and to propose a cost-effectiveness methodology that integrates epidemiologic and economic methods for future studies.

STUDY DESIGN:   Literature review. MEDLINE was searched from 1990 through 1999. Nine articles that met the inclusion criteria were reviewed. The methodological quality of the articles was critically appraised independently by two epidemiologists using standardized review criteria. Two health economists reviewed the studies on cost-effectiveness.

RESULTS:   The current literature suggests that chiropractors and physicians provide equally effective care for OLBP but that chiropractic patients are more satisfied with their care. Evidence on the relative costs of medical and chiropractic care is conflicting. Several methodological deficiencies limit the validity of the reviewed studies. No studies combine high-quality cost data with adequate sample sizes and controls for confounding factors.

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CONCLUSION:   Existing studies fail to clarify whether medical or chiropractic care is more cost effective. We suggest that future studies must combine epidemiologic and economic methods to answer the question adequately.



From the FULL TEXT Article:

Introduction

Back problems are the single most costly work-related injury. In 1992, back cases represented 24% of US workers’ compensation claims and 31% of costs [1]. Back problems are also common outside the workplace, and the distinction between work-related and non–work-related back pain is often uncertain. Approximately 11% of the adult population experience a disabling episode of back pain in any 6-month period, and nearly 80% of adults, including persons outside the labor force, experience one or more episodes of back pain during their lifetime [2,3].

Physicians and chiropractors are the primary caregivers for individuals with back pain [4–7]. Together they provide 80% of the care delivered per episode of pain. Despite the fact that physicians and chiropractors account for most of the costs of treating back pain, and treat the condition with distinctly different modes of care, there is a lack of convincing evidence regarding the relative cost-effectiveness of the care they provide [7].

In the economics literature, cost-effectiveness analysis is a mechanism for quantifying the values of alternative policies or treatments to determine if the expected benefits outweigh the expected costs, or to identify the policy or treatment that yields the greatest benefits for a particular cost. In cost-effectiveness analysis, expected benefits are expressed in health units (e.g., lives saved, hospital days saved, days of work absence saved) in the numerator of the cost-effectiveness ratio, while expected costs are expressed in dollars in the denominator. The resulting ratio indicates the benefit of a particular policy or treatment, in health units, per dollar expenditure.

A limitation found in the existing literature on medical and chiropractic care is the tendency to focus on only one dimension of the research question. Epidemiological studies focus on the effects of care on patients’ disability status, functional limitations, and symptoms (the numerator of the cost-effectiveness ratio), while economic studies focus on costs (the denominator). In either case, the other dimension of the issue, either health outcomes or costs, is ignored or poorly measured.

This article has two main objectives. First, we critically review and synthesize the recent literature on the cost-effectiveness of medical and chiropractic care for occupational low back pain. Second, we propose an integrated epidemiologic and economic methodology that will improve the design of cost-effectiveness studies of occupational low back pain.



Methods

      Search of epidemiological literature

A MEDLINE search covering the period January 1990 through April 1999 was conducted using Medical Subject Headings and text words, and the keywords low back pain, chiropractic medicine, and treatment. Titles and abstracts of the retrieved articles were screened to determine if a study met the following criteria for review: it is a randomized trial or cohort study; it compares the outcomes of patients receiving medical versus chiropractic care for low back pain; it includes measures of pain, functional status, or return to work; and it is written in English.

Seven of the 148 articles retrieved from MEDLINE met our inclusion criteria. Three randomized trials compare chiropractic care with physiotherapy, and four cohort studies compare chiropractic care with medical care. Studies of physiotherapy are included in medical management, because physiotherapy typically follows medical referrals but is not usually provided in concert with chiropractic care.

The randomized trials are appraised using criteria described by Van Tulder et al. (Appendix Table A1) [8]. The cohort studies are appraised using criteria developed at the Institute for Work and Health (IWH; unpublished; Appendix Table A2). The guidelines necessary to operationalize the IWH criteria are presented in Appendix Table A3. Two of the authors (PC and JWF) independently reviewed all papers. Disagreements between the reviewers were resolved by consensus.

      Search of economics literature

The articles reviewed for economic content were retrieved from a search of the Journal of Economic Literature, subject heading I1 (Health), from 1990 onward, and the MEDLINE search described above. A study must satisfy the following criteria to be included in the review: it is a comparison of medical and chiropractic care for low back pain, it includes information on the costs of care, and it satisfies accepted standards for controlling for confounding variables in the economics literature.

Five articles satisfy the inclusion criteria and were reviewed independently by the two economists (MLB and WGJ). The economic evaluations assess whether a study satisfies the following criteria for general methodology: it has adequate sample sizes, it uses appropriate methods to control for confounding variables, and it controls for differences in the case mix and severity of injury treated by physicians and chiropractors. In addition, the following criteria are used to evaluate the cost data in each study: the costs of health care are based on payments, rather than provider charges; the cost data account for patient-borne costs, including co-payments and deductibles; and the cost comparisons include disability costs and the costs of injury-related work absences.



Results

      Epidemiologic literature: chiropractic versus physiotherapy

The reviews of three randomized trials comparing chiropractic care and physiotherapy are summarized in Table 1. Two high-quality studies suggest that the two modes of care are equally effective in reducing symptoms and improving function for patients with low back pain. In a Swedish trial, individuals with acute and chronic back and neck conditions were randomized to receive chiropractic care or physiotherapy [9,10]. The choice of treatment modalities, and the frequency and duration of treatment, were at the discretion of each clinician. According to Skargren et al. [9], no differences in pain intensity, functional status, or self-reported general health status were reported at the end of treatment, or at 6 or 12 months after treatment.

In a 2-year follow-up study comparing chiropractic manipulation, McKenzie exercises, and an educational booklet, Cherkin et al. [11] report no differences between comparison groups with regard to bothersomeness of symptoms, disability status, days of work-related disability, or recurrence of pain. Patients receiving chiropractic manipulation or McKenzie exercises were, however, more satisfied with their care than those who received the educational booklet.

In contrast, a British trial suggests that chiropractic care is more effective in treating back pain than hospital-based outpatient physical therapy [12]. In this study, chiropractic patients show greater improvement in functional status in the short term and long term (2 years) than physiotherapy patients, but the size of the difference is small (7 points on a 100-point Oswestry scale). The results of the trial must be interpreted cautiously, however, because of possible selection and expectation biases associated with the accrual and randomization strategy. As acknowledged by Meade et al. [12], chiropractic treatments were more effective for patients who selected this type of care before the study assigned them to a chiropractor than for chiropractic patients who had initially selected a different type of provider.

      Epidemiologic literature: chiropractic versus medical care

The reviews of four cohort studies comparing chiropractic and medical care are presented in Table 2. Two cohort studies use workers’ compensation claims data to compare chiropractic and medical care for OLBP [13,14]. The descriptive results are similar in substance, but the methods of analysis and conclusions differ.

Studying claims data from injured Australian workers, Ebrall [13] compared between-group differences in mean outcome measures for 998 chiropractic patients and 998 physician patients (the latter drawn as a random sample from 3712 physician patients). Ebrall implicitly assumes that the random sample of physician patients has the same unmeasured characteristics as the chiropractic patients. The validity of this assumption is not, however, empirically tested. The study concludes that chiropractic care is associated with a larger proportion of medical only claimants who receive no disability benefit payments (a medical only claim is defined as a claim in which the worker returns to a job in less than the 5-day waiting period for wage loss benefits); fewer total compensation days for back pain; and fewer claimants developing chronic back pain.

Using workers’ compensation claims data from California, Johnson, et al. [14] also report a higher proportion of medical only claims among chiropractic patients. The authors’ approach differs from Ebrall’s study in that they analyze differences within claim types, comparing medical only claims treated by chiropractors with medical only claims treated by physicians. They then test the hypothesis that chiropractic care increases the probability of return to work within the 3- day waiting period by estimating a multivariate regression model with controls for age, gender, and other potential confounders. Lacking direct measures of severity, the authors estimate a variant of the model with controls for unobserved heterogeneity, that is, controls for systematic differences between the patients treated by physicians and chiropractors that are unobservable to the investigator. The authors assume the heterogeneity controls include a component that represents confounding differences in the severity of back pain.

The results with no controls for unobserved heterogeneity show that chiropractic patients have significantly higher probabilities of return to work within California’s 3-day waiting period than physician patients. The statistical significance of the effect disappears, however, in the models that include controls for heterogeneity. In brief, the conclusions of the Johnson et al. study agree with Ebrall that chiropractic patients return to work sooner than physician patients, but the Johnson et al. study attributes the difference in durations of work absence to unobserved differences in the characteristics of chiropractic and physician patients, rather than to the effects of chiropractic care. When controls for heterogeneity are included in the models, the authors find no statistically significant associations between type of care and 1) the probability of return to work within the 3-day waiting period; or 2) the incidence of permanent impairments; or 3) the duration of temporary disability benefits.

These two studies suffer from important methodological problems, and their conclusions must be interpreted accordingly. Many of the limitations are inherent in the use of claims data. The main flaws are difficulty in determining if the subjects are representative of the underlying population, because the characteristics of the underlying population are unknown; imprecise definition of back pain; inadequate measurement of the subjects’ baseline characteristics; questionable validity and reliability of the data on type of care received, because services are identified from codes on the billing data of health-care providers; inadequate controls for confounders, such as severity of injury, because claims data do not include clinical measures of severity and often omit ICD9 codes; and no description of the longer-term followup, because claims data do not provide information after a claim is closed (Table 2).

Using different outcomes, two other studies suggest that there is no difference in the relative effectiveness of chiropractic and medical care. In a cohort study conducted on North Carolina residents, Carey et al. [15] report that the time to functional recovery is similar for chiropractic and general-medical-practice patients, but that chiropractic patients are more satisfied with their care. The samples of patients were recruited from medical, orthopedic, and chiropractic offices. One third of the cohort was composed of patients with back pain with a workers’ compensation claim.

One important problem with the North Carolina study is that the nature of the underlying population is unknown. Approximately 65% of the invited primary care physicians, and 87% of the invited health management organizations agreed to participate in the study. Patients of the participating providers were then invited to join the study, but no information is provided on the patients or providers who refused to participate. No analysis of selection bias is included in the study. Carey et al. controlled for several confounding factors through multivariate survival analyses, but the potential for residual confounding because of self-selection or comorbidities remains an issue.

Finally, in a study of members of a health-care network in California, Hurwitz found [16] that the functional status of chiropractic and medical patients is similar 3 months after their initial visit. As shown in Table 2, however, several methodological flaws limit the validity of the results. Of particular concern is the low power of the statistical measures and the difficulty in identifying the inception period for this cohort.

      Economics literature: health-care costs

This section reviews five studies that compare medical and chiropractic care for back pain and estimate differences in the costs of the two modes of care. Two of the studies also analyze differences in the costs of work disability. The studies, with critiques summarized in Table 3, include the Carey et al., Johnson et al., and Ebrall articles described in the previous section, and additional studies by Nyiendo (published in three parts) and Stano [13–15,17–19]. A recent study by Williams et al. [20] is not included in our review, although it includes information on both health-care costs and durations of work loss for patients treated by a variety of providers. The study is excluded, because the results focus on the relationships between costs and differences in durations rather than on comparisons among providers. A number of earlier studies (see the articles cited by Nyiendo and the review by Manga) are also excluded from the discussion because of inadequate attention to methodological standards widely applied to economic evaluations of healthcare interventions [17,18,21].

Carey’s study of North Carolina back patients, described in the previous section, concludes that outcomes are similar for patients of physicians and chiropractors, but primary care physicians are lower-cost providers than either chiropractors or orthopedic surgeons [15]. The conclusion regarding costs is uncertain for at least two reasons. First, the data used to estimate the costs of health care are based on provider charges rather than payments. Provider charges are a biased measure of health-care costs, because payments for health-care services are typically discounted from charges, and the discounts vary among payers and providers. The Zenith Project, for example, shows that there are differences between the discounts applied to chiropractic charges and the discounts applied to physician charges [22]. The second problem with the cost comparisons is that the data on charges are not the charges submitted by the providers participating in the study, but average charges for services from a single insurer in North Carolina. Because of the missing data on health-care payments, and the likely errors in the data on charges, Carey’s conclusion that primary care physicians are the low-cost providers is extremely uncertain.

Stano’s article on the costs of chiropractic care is based on the largest number of cases studied to date [19]. The results are based on health insurance claims data for 7077 patients with 9314 episodes of care over a 2-year period. Responsibility for the outcomes of care is assigned to either physicians or chiropractors according to which type of provider delivered the first service in an episode of care. The cost data are appropriately measured in terms of payments rather than charges. The payments do not, however, include co-payments or deductibles borne by patients. The author uses categorical variables for co-payments and deductibles to adjust, as much as possible, for the effects of differences in patient-borne costs on the cost comparisons between chiropractors and physicians. Comparisons are made within ICD9-CM codes to control for potential differences in the average severity of injuries among patients in the respective provider groups. The health insurance data do not measure work loss days or indemnity payments for work absences.

The overall result is that average costs of care are lower for chiropractic patients than for physician patients. Much of the average cost differential is attributed to differences in the costs of hospital inpatient care. The importance of inpatient costs to the final results is addressed by the author, who indicates that “some (or even all) of the cost differentials could be explained by the hospitalization variable” [19]. In other words, the inclusion of a control for surgical or nonsurgical inpatient care would virtually eliminate statistically significant differences in the average costs of care. Stano suggests that he does not include a variable to control for hospitalization because, in his opinion, the evidence suggests that nearly all surgery for back pain is inappropriate. Nonsurgical methods of care are preferred to unnecessary surgery, regardless of provider type. The findings do not evaluate the relative cost effectiveness of chiropractors and physicians in the provision of nonsurgical care for back pain. That comparison is important, because surgery is not a treatment provided by chiropractors.

One remarkable feature of the results is that hospital inpatient costs represent a relatively large portion of total healthcare payments for chiropractic patients as well as physician patients, suggesting that assigning responsibility to providers based on first contact is not equivalent to receiving services from only one type of provider. Nearly 25% of adjusted total payments for chiropractic patients with ICD9846 (sprains and strains of the sacroiliac region), for example, is for hospital inpatient care. More than 40% of total payments for chiropractic patients with ICD9724.3 (sciatica, other, and unspecified disorders of the back) is for inpatient care.

The practice of assigning total costs to the type of provider first seen by a patient could introduce a systematic bias in the costs attributed to chiropractors. Consider cases who first see a chiropractor and eventually undergo back surgery. The average cost of surgical cases are, as the previous results suggest, quite high relative to nonsurgical care whether provided by chiropractors or physicians. The attribution of some costs of surgery to chiropractors because of the first provider assumption is not offset by a symmetrical assignment of high-cost chiropractor cases to physicians simply because chiropractors do not perform surgery. The extent to which the bias exists is, of course, an empirical question that can be answered only by an evaluation of the data.

      Economics literature: disability costs

Only a few articles, namely Ebrall [13], Johnson et al. [14], and Nyiendo [17,18], include information on both health-care costs and work-related absences for a study population. The results for all three agree that chiropractic patients are more likely to return to work within 1 week than physician patients. Nyiendo describes this finding as typical of nearly all previous studies of employed populations [17].

Nyiendo compares health-care costs and durations of work absence for workers’ compensation patients treated by chiropractors or physicians. Days of work absence are computed from beginning and ending dates of work loss periods recorded on workers’ compensation files. One of the most interesting features of the research is that the author has access to patients’ medical records. The principal limitation of the study is the small number of cases available for analysis. The results are based on 188 cases in the state of Oregon, with equal numbers of physician and chiropractic patients but no controls for differences in severity of back pain between the two groups. The author carefully details the limits imposed by the data and states that “the findings of this study emphasize the need for prospective studies of treatment outcome using similar patients in two or more provider groups” [18].

The costs of chiropractic care are found to be higher than the costs of medical care, primarily because the duration of treatment is longer for chiropractic patients. The author attributes the cost differentials to differences in case mix and severity of injury between patients in the two comparison groups. Specifically, Nyiendo reports that chiropractic patients are more likely to have chronic or recurrent problems, more likely to have risk factors that delay recovery, and more likely to be female than physician patients. The author does not estimate the extent to which the cost differentials change when differences in case mix and severity are controlled.

Nyiendo compares work loss time for chiropractic and physician patients but does not estimate the costs of work absences. The results do not measure, therefore, the extent to which differences in the costs of work loss time offset or increase the cost differentials for health care. Nor, as the author acknowledges, do the comparisons of work loss time control for other factors that influence return to work, such as the economic incentives associated with disability benefit payments. Given these limitations, the results show that chiropractic patients are more likely to return to work within 1 week than patients treated by physicians, but the difference is not statistically significant. One intriguing result is that work loss time for chiropractic patients with chronic problems is shorter than work loss time for patients with acute conditions [17]. The samples identified as “chronic problems” are not, however, restricted to persons with chronic pain, because the definition of “chronic” cases includes any worker who ever filed a previous job-related low back claim.

Ebrall compares average total costs (the sum of health care and disability costs) for workers’ compensation back cases treated by physicians and chiropractors [13]. He reports that average costs per case are lower for chiropractic patients than for physician patients, but the conclusion is driven by the relatively large proportion of chiropractic patients who do not receive disability benefits because they return to work within the waiting period. Ebrall’s conclusion, that chiropractors are the lower-cost provider, is questionable, because his approach implicitly assumes that chiropractic and physician patients are identical in the characteristics, other than health care, that influence durations of absence from work. In other words, the study assumes that the higher proportion of medical only claims among chiropractic patients results from more effective care, when it could result from confounding factors, such as differences in the severity of back cases treated by physicians and chiropractors.

One important question raised by the Nyiendo and Ebrall studies is whether chiropractic patients return to work more rapidly than physician patients, on average, because their capacity to function in the workplace is sustained by care that continues after a return to work. The Johnson et al. [14] study, discussed next, reports that average durations of work absence are shorter for chiropractic patients than for physician patients, but chiropractic patients are more likely to continue to receive care after they return to work. If continuing care permits earlier returns to work, the relevant research question is whether the additional costs of care are offset by the cost reductions associated with shorter durations of work absence.

Johnson et al. consider both the costs of health care and the costs of work loss days associated with back pain. The study excludes surgical cases, thereby eliminating some of the costs that were important in the Stano study. The authors recognize that some back surgeries may be unnecessary, but they do not have access to the health-care records needed to determine if unnecessary surgery was performed.

The authors assume that differences in the severity of back pain are included in the controls for unobserved heterogeneity in the models [14]. Estimates that include controls for heterogeneity show no statistically significant difference between chiropractic and physician patients in the probability of return to work within California’s 3-day waiting period. The authors conclude that chiropractors and physician are close substitutes in the treatment of back pain with neither provider offering a clear advantage in terms of cost.



Discussion

      The need for a cost-effectiveness methodology integrating epidemiology and economics

The purpose of our critical review is to synthesize current knowledge on the cost-effectiveness of medical and chiropractic care for low back pain and to identify conceptual and methodological deficiencies in the existing studies. The studies suggest that chiropractic and medical care (including physiotherapy) are equally effective in promoting recovery from OLBP but that patients are more satisfied with chiropractic care. Several methodological deficiencies, however, limit the validity of the reviewed studies.

The current literature on the effectiveness of medical and chiropractic care provides conflicting evidence that one type of care is superior to the other. As suggested by two high-quality randomized clinical trials conducted from general population samples, it is likely that both types of care are equally effective, but the generalizability of the results to workers’ compensation populations remains unclear [9,10]. The research consistently shows that chiropractic patients have shorter durations of work absence, on average, than physician patients [13,14,17]. There is no convincing evidence, however, that identifies whether the difference in durations is related to differences in the types of health care received or to intrinsic differences in the types of patients treated by chiropractors and physicians.

The methodological quality of the literature reporting on costs does not allow us to reach valid conclusions about the relative costs of medical and chiropractic care for OLBP. As yet, there are no studies that combine high-quality cost data with adequate sample sizes and controls for confounding factors.

Our critical appraisal has identified several sources of bias that jeopardize the internal and external validity of the observational studies. No study to date has used rigorous methodology to adequately study the cost-effectiveness of medical and chiropractic care. The next logical step in attempting to answer the cost-effectiveness question, therefore, is to study health outcomes and costs in a workers’ compensation population, with a study that combines epidemiologic and economic methodologies. While this appears simple in theory, it implies that two distinct research paradigms be merged and adapted to address a specific research question. Specifically, it entails the recruitment of a large sample of injured workers that will be followed for at least 1 year and for whom valid and reliable health outcomes information can be combined with accurate and complete cost data obtained from insurance companies and employers.

We propose that a cohort study is the design of choice to investigate the relative cost-effectiveness of medical and chiropractic care for work-related back pain. Although a randomized controlled trial is more appropriate to study the efficacy of treatments, a cohort study is best suited to investigate the effectiveness of already well-accepted and commonly used methods of care provided to injured workers. Further, there are two important drawbacks to implementing a randomized trial in this context. First, the ability to randomize injured workers to treatment groups is limited by state workers’ compensation laws. In the US, the choice of provider for the treatment of an occupational injury may reside with the worker, the employer, or both, depending on the state. Second, it has been demonstrated that randomizing patients with low back pain to types of care that are contrary to their preferences may result in significant selection and expectation biases [12]. Therefore, using an inception cohort design with extensive measurement and adjustment for confounding variables may offer the best strategy to study cost-effectiveness.

Defining an inception cohort to study occupational low back pain is challenging. The difficulty lies in ensuring that all subjects are at the same stage of their condition, in this case, early in their current episode. Therefore, defining the appropriate “time zero” is crucial. Given the natural history of low back pain, it is likely that a high proportion of injured workers have chronic or recurrent back pain and that they may be at different stages in the evolution of their condition when claims are filed. Because this may result in selection bias if subjects with chronic or recurrent back pain systematically select physicians or chiropractors, it is essential to ascertain any previous history of back problems and to control for this variable in multivariate regression analyses.

The selection of valid and meaningful outcomes measures is key to providing useful answers when studying low back pain. Deyo et al. [24] propose that standardized outcomes measures be used in this field of research. The proposed outcomes, which become the numerator of the cost-effectiveness ratio, include symptoms, functional status, general well-being, work disability, and satisfaction with care. The authors emphasize that the instruments selected to measure health outcomes must meet fundamental methodological criteria. First, an instrument should discriminate among individuals with different levels of severity of low back pain. Second, an instrument should be reliable and yield small variations between replicate measures. Third, an instrument should provide reproducible results if no real changes occur between two or more data collections. Fourth, when improvement or deterioration of the condition occurs, an instrument should be sufficiently responsive to detect small, but possibly clinically important, changes. Finally, an instrument must measure what it is supposed to measure, that is, it must be valid.

The cost measures, which become the denominator of the cost-effectiveness ratio, should be accurate and complete measures of the total costs of an episode of workrelated back pain from the viewpoint of a particular payer. From an employer’s viewpoint, for example, the costs of work-related injuries include the costs of health care and the costs of indemnity payments to injured workers, taking account of different insurance coverages and different mechanisms for experience rating insurance premiums. From a worker’s perspective, the costs of an episode of workrelated back pain include net wage losses during injuryrelated work absences and losses of income that result from lower productivity after a return to work. The costs of health care are not relevant in a cost-effectiveness study from the worker’s viewpoint, because the costs are fully covered by workers’ compensation insurance.

Regarding the analysis, the key issue in an observational study of different treatment modalities is whether the statistical adjustments for confounding variables adequately control for differences in subjects’ characteristics that affect the costs and outcomes measures. To implement the statistical controls, one must measure in all subjects, before treatment, the various factors that are known to influence the prognosis of OLBP. The measures are then included as covariates in multivariate regression models to adjust the observed differences in treatment effects, if any, for differences in the characteristics of the self-selected treatment groups that may affect outcomes. Chiropractors, for example, do not prescribe strong analgesics, so it might be expected that severity of back pain and attitudes toward pain will differ systematically between self-selected physician and chiropractor patients. Some of these pain variables are known to influence the outcomes of care, hence unadjusted comparisons of outcomes between the two treatment groups may be inaccurate, because the outcomes are confounded by the differences in pain-related aspects of OLBP.

The data must be analyzed with multivariate models, making the self-selected treatment groups as comparable as possible to mimic a randomized controlled trial that assesses treatment effects in an unbiased fashion. It can still be argued that some unknown confounder was unmeasured and, therefore, uncontrolled in the study design, but the credibility of this argument is greatly weakened when observed differences in outcomes fail to disappear as additional confounders are added to the multivariate model.

Once the differences in costs and outcomes of medical and chiropractic care have been accurately measured, with controls for confounding variables, the cost-effectiveness ratios can be computed. The cost effectiveness ratios compare the difference in health outcomes between physician and chiropractic patients in the numerator, with the difference in costs in the denominator. A large cost-effectiveness ratio indicates that medical care is relatively more costeffective than chiropractic care, and a small cost-effectiveness ratio indicates the opposite conclusion.

In sum, we have identified the following minimal criteria for a cohort study of the cost-effectiveness of medical and chiropractic care for OLBP: the sample is identified immediately after onset of back pain; the study obtains data on prior history of back pain; standardized outcomes measures are collected; the total costs of an episode of back pain are measured accurately; costs are evaluated from the viewpoint of a pre-identified payer; and multivariate models are used to control for differences in patients’ characteristics.



Conclusion

There is clearly a need for research on the different treatments for occupational low back pain that considers both health care and indemnity costs and controls for differences in severity of back pain at onset. It is virtually impossible, however, to conduct a truly experimental, randomized controlled trial of “largely chiropractic” versus “largely physician” care of back patients without either causing some unwanted effects by changing patients’ care preferences, or being forced to study only the minority of OLBP patients who apparently have no preference regarding type of provider. The great importance of the OLBP patient’s faith in his or her chosen caregiver, and the inextricable “placebo” effects of each form of care, make it difficult to conduct rigorous yet interpretable randomized controlled trials in this field, where no subject can be truly blinded to the type of care he or she receives. The provisions of state workers’ compensation laws also assign the right of choice of a medical provider to either workers or employers, and randomized assignments of patients would violate these rights. Thus, the most practical and generalizable evaluation design available is a prospective cohort study.

The failure of existing studies to clarify, definitively, whether medical or chiropractic care is more cost-effective for occupational low back pain arises, in part, because of methodological challenges. These challenges can be addressed only by combining the evaluation approaches of epidemiology (for health outcomes) and economics (for cost outcomes), and by capturing the best available measures of severity of back pain at onset, to the degree possible.



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    Chiropractic Journal of Australia 1992 (Jun); 22 (2): 47–53

  14. Johnson WG, Baldwin ML, Butler RJ.
    The costs and outcomes of chiropractic and physician care for back pain.
    Journal of Risk and Insurance 1999;66:185–206.

  15. Carey TS, Garrett J, Jackman A, et al.
    The Outcomes and Costs of Care for Acute Low Back Pain Among Patients Seen by Primary Care
    Practitioners, Chiropractors, and Orthopedic Surgeons

    New England J Medicine 1995 (Oct 5); 333 (14): 913–917

  16. Hurwitz EL.
    The relative impact of chiropractic vs. medical management of low back pain
    on health status in a multispecialty group practice.
    J Manipulative Physiol Ther 1994;17:74–82.

  17. Nyiendo J.
    Disabling Low Back Oregon Workers' Compensation Claims Part II: Time Loss
    Journal of Manipulative and Physiological Therapeutics 1991;14:231–239

  18. Nyiendo J.
    Disabling Low Back Oregon Workers' Compensation Claims. Part III:
    Diagnostic and Treatment Procedures and Associated Costs

    Journal of Manipulative and Physiological Therapeutics 1991 (Jun); 14 (5): 287-297

  19. Stano, M.
    The Economic role of chiropractic: Further analysis of relative insurance costs for low back care.
    Journal of the Neuromusculoskeletal System 1995;3:139–144.

  20. Williams DA, Feuerstein M, Durbin D, Pezzullo J.
    Health care and indemnity costs across the natural history of disability in occupational low back pain.
    Spine 1998;23:2329–2336.

  21. Manga P, Angus D, Papadopoulos C, Swan W.
    The Effectiveness and Cost-Effectiveness of Chiropractic Management of Low-Back Pain
    Ottawa: Kenilworth Publishing; 1993.

  22. Johnson WG, Baldwin ML, Burton Jr, JF.
    Why is the treatment of work-related injuries so costly? New evidence from California.
    Inquiry 1996;33:53–65.

  23. Cherkin DC, Deyo RA, Street JH, Barlow W.
    Predicting poor outcomes for back pain seen in primary care using patients’ own criteria.
    Spine 1996;21:2900–2907.

  24. Deyo RA, Battie M, Beurskens AJ, Bombardier C, Croft P, Koes B, Waddell G.
    Outcome measures for low back pain research: A proposal for standardized use.
    Spine 1998;23:2003–2013.



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