Measuring practitioner/therapist effects in randomised trials of low back pain and neck pain interventions in primary care settings

Abstract

In psychological health treatment studies it has been shown that differences between therapists account for some of the non-specific effect of treatment but this phenomenon has not so far systematically been investigated in musculoskeletal disorders. In this study we evaluated and compared the size and potential influence of the 'practitioner effect' (or 'therapist effect') in three randomised treatment trials of low back pain and neck pain patients in primary care. We calculated the proportion of variance in outcomes attributable to differences across practitioners, i.e. the practitioner-variance partition coefficient (p-vpc). As measures of outcome, we focused on self-reported disability as the primary outcome, but we also investigated assessed psychological outcomes. The p-vpc for the disability measures ranged from 2.6% to 7.1% across trials and time points (post treatment and follow up). Estimates differed between treatment subgroups within trials; being highest in treatment subgroups assigned to psychosocial-based interventions. A 'practitioner effect' does exist and is more pronounced in treatments involving greater psychosocial emphasis. This has implications for both practice and research in this clinical area. It highlights the importance of patient-practitioner interactions, and the need to address practitioner effects in designing and analysing outcome studies in low back pain and neck pain in primary care.

The Chiropractic Hospital-Based Interventions Research Outcomes Study: Consistency of Outcomes Between Doctors of Chiropractic Treating Patients With Acute Lower Back Pain

“…Neither the study of Lewis et al 27 nor our study controlled for differences in the quality of the practitioner-patient relationship or for other unmeasured nonspecific effects that could have easily confounded the true treatment effects. We speculate that underlying differences in the effects of treatment expectation and the practitioner-patient relationship may account for at least some of the discrepancy between our findings and those of Lewis et al 27 Although practitioner effects have not been previously documented among DCs, they have been studied among other clinicians. According to Simon et al 40 , most studies of practitioner effects are from psychotherapy and clinical psychology, where therapists account for up to 18% of the unique variability in patients' outcomes.…”

“…For now, however, we feel our findings are strong enough to at least mildly unsettle our prior assumption-and prior declaration to our referring primary medical physicians-that outcomes are likely consistent between different evidence-based providers of SMT. Also in the meantime, our finding that pain-specific disability varied significantly between DCs somewhat conflicts with the findings of Lewis et al 27 Upon reanalyzing data drawn from 2 earlier randomized trials 38,39 Lewis et al 27 found that disability outcomes did not vary significantly between different physical therapists administering either "exercise plus advice and manual therapy" or "physiotherapy including manual therapy techniques." However, in the study of Lewis et al 27 , the effect estimates were not adjusted for differences in patients' baseline characteristics, whereas in our study, we carefully controlled for clinical characteristics through the use of restrictive inclusion/exclusion criteria and statistical adjustments for age, sex, and baseline outcome measurements.…”

“…However, a previous study of the effects of individual physical therapists on outcomes for neck and LBP showed that 3% to 7% of the total variance in pain-related disability scores could be attributed to differences between practitioners. 27 On the other hand, these practitioner effects were less (0%-3%) for patients receiving manual therapy and practically nonexistent (0.3%-0.5%) when the treatment (consisting of combined physical therapy and manual therapy) was applied in a standardized manner.…”

Effectiveness and costs of a vocational advice service to improve work outcomes in patients with musculoskeletal pain in primary care: a cluster randomised trial (SWAP trial ISRCTN 52269669)

“…The sample size takes into account (1) 30% inflation through clustering of data (at practitioner level) based on an intracluster correlation coefficient for betweenpractitioner effects of 0.05, 22 variation in expected VA service referral rates between GPs (based on an expected coefficient of variation of 0.65), 11 and (2) 25% inflation through allowance for 20% loss to follow-up at 4 months. This resulted in a required sample size of 330 participants (165 per arm).…”

New Developments in the Psychological Management of Chronic Pain

“…Pressure on service delivery is such that the driving force to disseminate an apparently effective treatment has been greater than our knowledge of the factors that determine the effective delivery. Although it is clear that there are differences between therapists in their effectiveness, 33 as Ehde et al 34 note, "The degree to which the training, experience and interpersonal qualities of the CBT interventionist, affect CBT outcomes is unclear." p 159…”