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Various clinical and sociodemographic risk factors were identified that have implications for occupational health and health policy. However, there was a lack of good-quality research investigating the predictive nature of many other variables.

For many randomised trials preference may be an important prognostic variable. In such circumstances, preference should be taken into account in the final analysis. This study demonstrates it is sometimes feasible to randomise patients to their less preferred treatment, thus allowing more robust statistical comparisons between randomised groups. This modification may make RCTs more rigorous and improve their external validity.

A cognitive behavioral approach was previously compared to a biomechanical approach (the McKenzie method) for the treatment of patients with back and neck pain in a randomized trial. Few differences between the treatment interventions were found. The aim of this secondary analysis was to determine if any clinical characteristics distinguished those patients who responded best to the McKenzie approach. Treatment success was defined as 50% reduction in original functional disability scores (Roland-Morris Disability Questionnaire or Northwick Park Neck Pain Questionnaire); failure to achieve this was defined as treatment failure. A liberal definition of success was 50% improvement retained at either 6 or 12 months, whereas a strict definition of success was 50% improvement at both 6 and 12 months. Ten variables were screened by univariate regression analysis to see if they predicted success. Any significant variables (P < 0.1) underwent multiple regression analysis. Only 21 and 16 patients out of 102 were deemed treatment successes according to the liberal and strict definitions, respectively. With the liberal definition, only centralization (P = 0.065), spine region (back rather than neck pain) (P = 0.089), and duration of pain (P = 0.001) emerged as predictors from the univariate regression analysis. With the strict definition, only the latter two variables emerged: spine region (P = 0.026) and duration of pain (P <0.01). All these variables were retained in the multiple regression analysis. In this study, duration of pain was the strongest predictor of success, although back pain and centralization had some predictive ability.

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