Regression analysis. Regression analysis of the improvement in interference with work from study beginning to end and ‘30% pain responders’, expressed as risk ratios [RR, red colour] or risk differences [RD, blue colour]. Interference with work was measured on a scale of 0–10 points. The size of the symbols represents the weights of the individual studies in the regression analysis (inverse variance). Regression lines are solid; broken lines mark the 95% confidence intervals.