Second, due to the retrospective design of this current study only parent-reports (ECBI) were available for the measurement of treatment outcome effects. As mentioned earlier, the lack of Dutch norms for the ECBI have consequences for the interpretations of the results in the Dutch context. Thereby, the normal range of functioning of a child on the ECBI is a part of the mastery criteria to terminate PCIT. Hence, more information on parent personality characteristics, parenting stress and child behaviour would provide a wider range of information for the treatment outcomes. This information is highly recommended for future research to address questions concerning the effectiveness of PCIT on other parent and child functioning areas. Furthermore, observational measures using the Dyadic Parent–child Interaction Coding System (DPICS) [48] are recommended for providing more information about the behaviours, as well as the quality of parent–child interactions. The inclusion of a diagnostic interview for concerning child behavioural problems and the use of more independent sources (e.g. teachers) could have also improved the study.