Description

Design: Single-site, parallel-group, three-arm randomized controlled trial at İstanbul Nişantaşı University, Istanbul, Türkiye.

Participants: Students aged 18 years or older enrolled in medicine or health-sciences programs (medicine, psychology, nursing and dentistry), recruited through announcements (student WhatsApp groups, e-mail and brief in-class presentations). Participation is voluntary and has no effect on academic standing.

Arms: (1) Bibliotherapy with the self-help book "Zihninde Çok Kuran İnsanlar için Salma Rehberi"; (2) bibliotherapy with the self-help book "Çapa Atmak"; (3) waitlist control, assessment only during the study period, with books provided at the end of the study. Reading is self-paced over 8 weeks without therapist contact.

Randomization: After completion of baseline assessments, participants are allocated 1:1:1 using a computer-generated random sequence (Randomizer.org). Faculty and baseline DASS-21 total score are taken into account to support balance between groups; the DASS-21 score is not used as an inclusion threshold. The allocation list is stored securely by the research team, and allocation is not disclosed until baseline assessments are complete.

Sample size: G\*Power 3.1, medium effect size (f = 0.25), three groups, α = 0.05, power 80%: minimum 159 participants. 165 participants (55 per arm) are targeted.

Measures and schedule: Sociodemographic form at baseline. Depression Anxiety Stress Scales-21 (DASS-21), Cognitive Attentional Syndrome Scale-1 (CAS-1) and Metacognitions Questionnaire-30 (MCQ-30) at week 0, week 4 and week 8, collected online through a study website after electronic informed consent. Process measures: a weekly one-item reading log in the two bibliotherapy arms, and a three-item contamination form at week 8.

Telephone contact: All participants, including the waitlist group, receive brief standardized telephone calls at weeks 2, 4 and 6 to confirm participation, reading progress and completion of forms. Calls follow a fixed script, serve reminder and confirmation purposes only, and contain no therapeutic content or guidance about the books, so that contact intensity is equal across arms.

Safety: Participants with current psychiatric treatment, a recent change in psychotropic medication, bipolar disorder, acute psychotic symptoms or suicide risk are not included. If questionnaire responses indicate a high level of distress during the study, the research team contacts the participant and refers them to appropriate mental health services.

Analysis: Repeated-measures ANOVA (or non-parametric alternatives) to examine group × time effects, with baseline scores taken into account; partial eta-squared is reported as the effect size; intention-to-treat principles are applied for missing data. SPSS is used.

Data protection: Participants are identified only by study codes. Telephone numbers are collected with consent for study contact only and stored separately from the dataset. Data are stored under encryption in accordance with Turkish personal data protection law (KVKK), and no personal identifiers appear in reports or publications.