RESUMEN
INTRODUCTION: Animal-assisted psychotherapy is an emerging field with great potential and growing popularity. However, empirical research on its effectiveness is insufficient, and consistent evidence about patients' commitment is missing. The present meta-analysis addresses this gap by systematically comparing drop-out rates in animal-assisted psychotherapy and by relating the resulting across study drop-out rate to across study drop-out rates reported in meta-analyses on conventional psychotherapy. METHOD: Fifty-seven studies published until August 2022 were identified as eligible for meta-analytic comparison, that is, they conducted animal-assisted psychotherapy on at least one group of psychiatric patients and reported drop-out rates. Potential moderating influences of the type of animal and patients' disorder were considered, as well as multiple other demographic and study design variables. RESULTS: The across study drop-out rate in animal-assisted psychotherapy was 11.2%. This was significantly lower than the across meta-analyses drop-out rate of conventional psychotherapy (d = -.45, p = .0005). Although effects of moderator variables could not be evaluated statistically due to too small and heterogeneous data sets, descriptive results suggest influences of the type of animal and patient disorder. However, study quality ratings identified serious shortcomings regarding proper research design, most critically concerning the report of effect size measures, the use of standardized intervention plans and Open Science practices. CONCLUSION: Drop-out constitutes a major problem of psychotherapeutic research and practice. By proposing that the inclusion of an animal in the psychotherapeutic setting can enhance patients' commitment and by outlining challenges and opportunity of animal-assisted psychotherapy, this meta-analysis offers a starting point for future research in this evolving field.