Fidelity
Procedural fidelity was accomplished by the use of a manual that described all components of the intervention. Adherence to the intervention protocol was measured by percentage of addressed session components. After each session, the therapist had to fill in a checklist including all session components. Additionally, all sessions were audiotaped and listened back by the first author (RH), to check if all topics were covered in the sessions, and to assess if contamination occurred. Contamination was defined as (a) consequent-based techniques that were addressed in the antecedent-based sessions, (b) questions or remarks from the therapist that could result in the parents to think of consequent-based techniques in the first two sessions, or (c) no adequate reaction from the therapist on remarks or questions from the parents that had to do with consequent-based techniques in the antecedent-based sessions, based on the procedures of 