„Intention to treat“ oder „treatment as received“ – Umgang mit Abbrechern in der Forschung zur Straftäterbehandlung: Methodische Überlegungen und Beispiele aktueller Studien

Lack of internal validity is a frequent problem in evaluation studies of offender treatment, as randomized controlled trials are difficult to implement and comparison groups in quasi-experimental studies are often not completely equivalent. Special matching procedures or statistical control of selection bias by using potentially interfering variables as covariates can provide a solution to some of these problems; however, a high dropout rate from offender treatment programs presents another problem, as the variables that cause attrition are often risk factors for reoffending. It is argued that a treatment-as-received (TR) approach which compares treatment completers with the comparison group may confound genuine treatment effects with selection effects. Particularly high recidivism rates in dropouts may be due to negative effects of attrition (e.g. stigmatization) but may more likely reflect a higher a priori risk for reoffending. Using data from some recent treatment studies, the authors show that alleged positive effects often disappear when a more adequate intention-to-treat (ITT) approach is used in which dropouts are retained in the treatment sample.