Results
The intention-to-treat analysis showed favourable intervention effects over time for relationship quality, explained by a higher intervention group score at T2. An intervention effect was found for parental interest in other prison-delivered treatments at T2. The analysis per protocol found similar but stronger effects on the relationship quality and an additional intervention effect over time for criminal attitude, also explained by a significant group difference at T2. The effect on treatment interest did not reach statistical significance in the analysis per protocol. Group leaders reported that all sessions had been performed and the objective ratings of fidelity rendered overall acceptable delivery of the intervention.