134 Chapter 5 Follow-up assessments took place at 3, 6, 9, 12, and 18 months after baseline assessment. Written informed consent was obtained from participants prior to baseline assessment. More details about the RCT can be found in our study protocol, which was prepared according to the SPIRIT 2013 statement (Chan et al., 2013; Swinkels et al., 2020). The Medical Ethics Committee of the Amsterdam University Medical Center (NL60308.029.17) reviewed and approved the RCT prior to data collection. The study is registered at the Netherlands Trial Register (NTR7163). The CONSORT 2010 Checklist was used to report this study (Schulz, Altman, & Moher, 2010), see Appendix C. Participants Sample size The power calculation for a repeated measured design, conducted in Stata (Stata Statistical Software: Release 16, 2019), showed that a total of 68 participants were required to detect a small-to-medium effect size (Cohen’s F = 0.20) in a pairwise comparison of pre-post change between two active treatment arms, with a power of 0.80 and a within-person correlation coefficient of 0.50. We aimed to include 105 participants to account for 30% expected dropout from the intervention. Inclusion and exclusion criteria Participant were forensic psychiatric outpatients receiving treatment at Inforsa Forensic Outpatient Care. Patients were included if they (1) received at least 3 months in treatment and could adhere to appointments with their clinician, (2) were aged 16 years or older, (3) were diagnosed with a psychiatric diagnosis by a clinician according to the DSM-IV-TR/5, (4) had limitations in social network and social participation identified by their clinician and a research assistant using the Self-Sufficiency Matrix (Fassaert et al., 2014), and (5) were not completely satisfied with their social relationships, as defined with a score of 5 or below on one item of the Manchester Short Assessment of Quality of Life measuring the self-reported quality of social relationships on a 7-point Likert scale (Priebe et al., 1999). Patients were excluded if, before or at baseline assessment, (1) acute psychotic symptoms, (2) acute suicidality, (3) severe addiction problems requiring immediate intervention, and (4) a high risk for severe aggression towards clinicians or others were identified. Finally, patients could not participate if they were enrolled in other scientific research projects at Inforsa.
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