Given the high prevalence of mental health issues, such as anxiety and depression, in pretrial detainees, the Swiss Federal Justice Department (SFJD) approved a model trial ("Modellversuch Untersuchungshaft", MV). The MV will be carried out in 11 pretrial detention facilities in the cantons of Zurich and Bern and aims to improve the wellbeing and social integration of individuals in pretrial detention. As part of the MV the investigators are evaluating the impact of two interventions using a randomized controlled trial (RCT). The first intervention, "Prison Stress Management" (PRISMA), addresses the issue of poor mental health of inmates during pretrial detention and after release. PRISMA is a scalable World Health Organization (WHO)-developed psychological intervention based on cognitive-behavioral therapy (CBT) program and goes beyond the status-quo mental health support offered in jails. Currently, only inmates with severe mental health problems are referred to the psychiatric ward of the health services provided in jails and no continuation of support is offered after the transition to the outside world. The second intervention (SOCIAL) uses extended social services to address potential disruptions incarceration might cause in detainees' social and economic lives. The isolation from the outside world implies that detainees might lose their jobs and housing, their relationships with their family and friends are strained, all factor hindering re-integration into society and taxing their mental wellbeing. This project will provide much needed insights to criminal justice authorities to design detention facilities and the detention experience in ways that empower incarcerated individuals to cope with the disruptions and psychological stress that come along with their detention.

The RCT will inform about the effect of PRISMA.

The sample size is determined by the enrollment window (from November 27, 2023 to September 30, 2026). Based on historical data, the investigators expect roughly 5,100 subjects to enter pretrial detention in the cantons of Zurich and Bern during this period.

Of the projected 5'100 people entering pretrial detention during the enrollment window, it is expected that roughly 43% (or 2'194 individuals) will be eligible for PRISMA and roughly 65% (or 3'316 individuals) will be eligible for the proactive social services intervention, respectively. Thus, it is expected that 1'428 individuals (or 28% = 43% of 65%) to be eligible for both interventions and, hence, constitute randomization sample C. This means that 766 individuals (= 2'194 - 1'428) will be eligible for PRISMA only (randomization sample A) and 1'888 individuals (= 3'316 - 1'428) for proactive social services only (randomization sample B). 1'018 (= 5'100 - 1'428 - 766 - 1'888) individuals will not be eligible for any of the two interventions. If samples are split with equal probability into experimental groups, the investigators expect the following group sizes:

Randomization sample A:

REGULAR PRETRIAL: 383 PRISMA: 383

Randomization sample B:

REGULAR PRETRIAL: 944 SOCIAL: 944

Randomization sample C:

REGULAR PRETRIAL: 357 PRISMA: 357 SOCIAL: 357 PRISMA & SOCIAL: 357 For the analysis, observations from the REGULAR PRETRIAL and the PRISMA group from randomization samples A and C, respectively, will be pooled. This leaves N = 1480 participants who will be involved in the RCT (assigned to either receiving the PRISMA intervention (N=740) or control condition (REGULAR PRETRIAL) (N = 740)).

This preregistration focuses on the short-term effects of PRISMA on mental wellbeing and therefore only considers the REGULAR PRETRIAL and PRISMA treatment arms. See "Mental Health Intervention and Social Service in Pretrial Detention" on www.socialscienceregistry.org for preregistration of the other treatment arms.

Inclusion Criteria:

• • Entering pretrial detention inmate in any of the 11 pretrial detention facilities in the Cantons of Zurich and Bern

  • aged ≥ 18 years

Exclusion Criteria:

• Not fluently speaking any of the nine languages in which PRISMA is offered: German, Albanian, Arabic, English, French, Italian, Romanian, Serbian/ Croatian, Spanish

  • Acute suicidality
  • Not interested in PRISMA and its randomized evaluation

All instruments and questions will be administered online.