The PACE trial in chronic fatigue syndrome/Authors' reply

The source for this defi nition of clinically useful diff erence states that such a method has a "fundamental limitation": "estimates of variability will diff er from study to study...if one chooses the between-patient standard deviation, one has to confront its dependence on the heterogeneity of the population under study".2 In White and colleagues' study, we do not have heterogeneous samples on the Chalder fatigue questionnaire and short-form 36 physical function subscale, since both are used as entry criteria.1 Patients had to have scores of 65 or less on short-form 36 to be eligible for the study.1 However, most, in practice, would probably need to have scores of 30 or more to be able to participate in this clinic-based study. [...] we com pared the results and however we defi ned CFS and myalgic encephalo myelitis, we found that cognitive behaviour therapy and graded exercise therapy provided a signifi cant and clinically useful advantage of moderate size over adaptive pacing therapy and specialist medical care, but were no less safe.