Participants in this group (all participants) were asked to complete a questionnaire before and after (6 weeks after baseline) using the online self-help intervention (unguided web-based intervention).

An online unguided intervention based on Cognitive Behavioural Therapy and elements of Dialectical Behaviour Therapy, Problem Solving Therapy, and Mindfulness Based Cognitive Therapy. The intervention consists of 6 modules with each a theoretical part, a weekly assignment and (optional and mandatory) exercises. Participants are advised to complete one module weekly. The original intervention was adapted to students (language, addition of podcasts, examples that were more suited to their lives).

A 21-item self-report questionnaire to measure (the severity of) suicidal ideation in adolescents and adults. Each item is rated on a scale from 0 to 2, resulting in a total score ranging from 0 to 38, with higher scores indicating more (severe) suicidal ideation.

A 21-item self-report questionnaire to measure (the severity of) suicidal ideation in adolescents and adults. Each item is rated on a scale from 0 to 2, resulting in a total score ranging from 0 to 38, with higher scores indicating more (severe) suicidal ideation.

A 4-item self-report questionnaire to measure hopelessness in adolescents and adults. Each item is rated as 'true' (score = 1) or 'false' (score = 0) for them over the past week, resulting in a total score ranging from 0 to 4, with higher scores indicating higher levels of hopelessness.