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Background: Despite a long tradition of discussions on the evaluation of psychotherapy, there is still a lack of agreement for measuring change after psychological treatment. In this paper we describe the concept of statistical and clinical significance of change. We use the Symptom Checklist 90 R as a commonly administered instrument to propose conventions and cutoff points for psychological symptoms and their change after therapy., Method: A German norm population and several psychotherapy samples have been aggregated to calculate cutoffs and confidence intervals (reliable change indices) for statistically and clinically significant changes after psychotherapy., Results: The cutoff point between a 'functional' and a 'dysfunctional' population was calculated as C = 0.57 (Global Severity Index, GSI). Patients above this score need a change of at least RCI = 0.43 (GSI difference) for a statististically significant change. Below this score the RCI = 0.16. The use of multiple clinical groups (e.g. inpatients and outpatients) for a more realistic determination of a 'stepwise' clinically significant change, as proposed by Tingey et al. in the USA, is not possible in the German samples collected so far. Initial SCL 90-R scores in these groups do not show enough differences to call a move from one group to the other a clinically significant change., Conclusion: In the German samples investigated the move from a 'functional' to a 'dysfunctional' population and vice versa has to be taken as the criterion for a clinically significant change up to now.