[Therapeutic Factors in Offender Treatment: A Systematic Review]

This paper presents a systematic literature review of international research on therapeutic factors in offender treatment. The review was based on the PRISMA criteria; PsycINFO and PSYNDEX as well as references given in included studies were browsed. Only quantitative empirical studies published between 1990 and 2018 were included. In this paper, evidence for common factors (therapeutic alliance, social climate, feedback) and therapist factors (interpersonal skills/characteristics, personality, therapy expectations) from 19 journal articles are reported. Some tendencies emerged, but there was no conclusive evidence on the effect of common factors and therapist factors on the therapy outcome. This non-conclusive evidence is mostly due to the methodological shortcomings of primary studies, heterogeneity of outcome variables and the low number of studies that looked at each of these variables. In sum, there is not enough evidence to date to show a strong relationship between common factors and therapist factors and a (positive) outcome in the treatment of offenders.