Margit Kooijman

102 Introduction Why do some patients recover and others don’t? This key question for patients, clinicians and researchers, has for patients with musculoskeletal pain mainly been addressed by studying the effects of different treatment options. To date, not one type of treatment can clearly be favoured over another 1,2 . In fact, an evaluation of different studies found that less than 2% of the total variance in outcome was actually explained by treatment across trials 3 . Treatment is delivered by different therapists. Therefore, it is plausible that variability in treatment outcome is also influenced by differences between practitioners. This so-called ‘therapist effect’ has been established in psychotherapy professions and shown to account for between 0-18% of variability in patient outcomes 4 . Research within the field of primary care physiotherapy exists but is much scarcer. One study on patients with low back and neck pain compared three RCTs in which a wide variation of treatment types was applied. Therapist effect was found to account for 3-7% of the variance 3 . A recent observational study on patients with chronic diseases confirmed a therapist effect to account for 7% 5 . In general medicine and psychotherapy, it is known that personality traits of the clinician affect patients and effect outcome 6 . Within the field of physiotherapy, one study on patients with chronic diseases found that therapists that tend to be calmer and more secure (less neurotic) produce better treatment outcomes 5 . Other research identifying which factors explain therapist effect is limited mostly to age, experience and education and shows conflicting results and small effects 7 . So, exploration of the ‘therapist effect’ is needed to further elucidate factors attributing to recovery. In this study, the influence of personality of the physiotherapists was explored using the Big Five Inventory (BFI) questionnaire 8 . This questionnaire captures the commonalities among the existing systems of personality description and thus provides an integrative descriptive taxonomy for personality research. It investigates five domains of personality as summarized by the broad concepts of extraversion, neuroticism, agreeableness, conscientiousness, and openness to experiences 9 . Shoulder pain is the most common complaint in the average physiotherapy practice after lower back and neck problems 10 . It has an unfavourable long-term outcome in many patients concerning pain and impairment of ordinary activities of daily living, as about 40-60% have recovered within six months to two years 11,13 . Despite its commonness, as yet only few prognostic factors (duration of complaints, pain severity and concomitant neck pain) have been identified 14 . Although longer duration of complaints is known to predict poorer outcome, many patients already have chronic complaints (> 3 months) before they see a physiotherapist. This requires therapists to deliver psychosocial and behavioural focused treatment strategies, in which a practitioner effect is known to be more pronounced than, for example, in manual therapy 3 .