Proposal of Measurement Occasions for Unbiased Evaluation of Psychotherapy

Studies complementing the assessment of symptoms right before (t₁), right after therapy (t₂), and at follow-up (t₃) with an assessment of symptoms preceding the waiting period without intervention (t₀) have revealed substantial t₀–t₁ changes. We discuss this phenomenon based on our own data and address the following questions: does it make sense to compare symptoms at the beginning of therapy (t₁) with symptoms at the end of therapy (t₂) or at follow-up (t₃)? Or does it make more sense to use t₀ instead of t₁? We argue for the latter alternative based on the following reasons. (1) Symptom descriptions at t₀ are realistic. (2) Expecting therapy success mitigates symptom descriptions at t₁. (3) Security signals emitted from the therapy context also mitigate symptoms, especially anxiety, at t₁. (4) Regression toward the mean reduces the validity of single occasion assessments. Controlling for regression requires two occasions of measurement with a short time interval at t₀ (t₀₁ and t₀₂). It follows from this reasoning that therapy success should be evaluated using the t₀₂–t₂ and t₀₂–t₃ intervals. Single case evaluations require reliable critical differences. This will be illustrated using a concrete example. The validity of treatment evaluation can be increased via the elimination of non-pathological symptom scores. A simplified calculation of cut-off scores can facilitate applied treatment evaluation. Unspecific t₀–t₁ changes do not challenge therapy effects according to t₁–t₂ changes. Rather, they are part of the whole therapy process.