Preliminary Efficacy of the Portuguese Adaptation of Metacognitive Interpersonal Therapy for Male Domestic Offenders (MIT-MDO-PT) in Men Under Judicial Supervision for Intimate Partner Violence With Personality Disorders: A Preregistered Multiple-Baseline Single-Case Experimental Design With Partner-Reported External Validation

Background. Court-mandated psychoeducational programmes for intimate partner violence (IPV) perpetrators show small or null effects on recidivism and high attrition, particularly among men with personality pathology. Metacognitive Interpersonal Therapy (MIT) targets the metacognitive dysfunctions (monitoring, differentiation, integration, decentration, mastery) and maladaptive interpersonal schemas that underlie personality disorders. Its adaptation to male domestic offenders (MIT-MDO) has shown promising results in a proof-of-concept case series (Pasetto et al., 2026). The European Portuguese adaptation (MIT-MDO-PT) was developed following established cross-cultural adaptation standards and is preregistered separately (osf.io/r2x8g). The study protocol is registered on the Open Science Framework (osf.io/wqpnc; update v3.1, September 2026).

Design. Nonconcurrent multiple-baseline single-case experimental design across participants (single series; participants enter at different calendar times). Phase A (baseline): weekly monitoring with a target of five data points (minimum of three only when imminent risk requires earlier treatment; no data-dependent extension), using the brief monitoring set (CTS2 physical assault and psychological aggression subscales, 1-week recall, plus CORE-10). Phase B (intervention): 24 individual weekly sessions. Treatment onsets are fixed a priori, before baseline data are inspected, and staggered by at least three weeks between participants irrespective of referral pathway, so that the A-to-B change occurs at each participant's own onset rather than at a common calendar time, controlling for maturation, history and instrumentation drift. No randomization. Outcome assessment at T0, T3 (including the SCID-5-PD) and T4 is performed by the same assessor, independent of the therapist; the weekly series is self-completed on a secure platform before each session without the therapist present. Treatment fidelity is rated blindly on 20% of sessions by an independent rater (inter-rater ICC target >= .80 on 10% of rated sessions). Participants at imminent risk of harming the victim move directly to treatment, and the deviation is reported.

Assessment schedule. T0 (baseline): complete battery. T1 (after Session 8): CTS2, MSAS, CORE-OM, IRI. T2 (after Session 16): T1 set plus EDRE, IIP-32, TOSCA-3. T3 (after Session 24): complete battery and exit interview. T4 (8-10 weeks after Session 24): CTS2, MSAS, PID-5, IIP-32, CORE-OM, TOSCA-3, IRI. Weekly throughout Phases A and B: CTS2 physical assault and psychological aggression subscales and CORE-10 (act counts, 1-week recall). CTS2 at T1-T4 uses a "since the last assessment" recall period. Recorded violence-related incidents (new police or judicial occurrences, breaches of the judicial measure notified by DGRSP, activations of the hospital safety protocol) are logged per participant and phase as an objective secondary outcome; a serious adverse event is defined a priori and a study-level stopping rule applies. Screening for psychopathy: candidates meeting SCID-5-PD criteria for antisocial personality disorder complete the Self-Report Psychopathy Scale - Short Form (SRP-SF, Portuguese version); a total score of 70 or above is exclusionary. WAI-SR at Sessions 4, 8, 12, 16, 20 and 24.

Partner assessment. Administered exclusively by the victim-support team of Hospital Beatriz Angelo at T0 and T3, in fixed order: Danger Assessment-5 first (an elevated score immediately triggers the hospital safety protocol), then CTS2 partner version and PMWI-SF. Partner data are stored by the hospital separately from the research database; the research team receives de-identified data only. Two to five complete dyads are expected.

Analysis. No group-level inferential models. Per participant: reliable change index (Jacobson & Truax) with |RCI| >= 1.96; percentage of non-overlapping data (PND >= 70%) and non-overlap of all pairs (NAP >= 0.66) on the weekly series, with Tau-U (uncorrected as the main index; trend-corrected as sensitivity analysis) and baseline-to-treatment rate difference; structured visual analysis following a named protocol (level, trend, variability, immediacy, overlap, consistency). Partner-exposure stratum (cohabiting, regular contact, no contact) is recorded and reported for the interpretation of the weekly IPV series. Participant-level decision: RCI criterion met plus at least one corroborating criterion. Study-level support when replicated in at least 3 of 5 participants (at least 4 if N = 6-7). Temporal precedence of metacognitive change over violence reduction examined by visual analysis (exploratory). Dyad-level concordance and change in number of personality disorder diagnoses are descriptive. Missing items below 20% within a scale are imputed by person mean; 20% or more, the score is not computed; no imputation of weekly series; last observation carried forward only as sensitivity analysis. Analysis code is written before data access.