Therapist effects on treatment outcome and treatment length in routine care seem to be relevant predictors in the context of feedback studies. Therapists' attitudes toward and use of feedback as well as patients' attitudes toward feedback should be further investigated in future research on psychometric feedback.

Sample size tables, including varying sample size conditions, were constructed and study examples given. This study gives an insight into the potential size of the TE and provides researchers with a practical guide to aid the planning of future studies in this field.

No abstract

The original version of this article unfortunately contained a mistake. In Results section, under the heading the "Application", CI difference values were incorrect in one of the sentences. The corrected sentence is given below.