A Single-Arm Trial of a Web-Based Acceptance and Commitment Therapy Mental Health Promotion Intervention for University Students (YOLO UQ)

The study includes two assessment pathways (Full research Arm and Minimal research Arm), but these do not constitute separate intervention arms because all participants will receive immediate access to the web-based YOLO program after providing informed consent. The intervention consists of four online modules, each based on the core principles of Acceptance and Commitment Therapy (ACT), and participants will be encouraged to complete one module per week. The program is designed to promote psychological flexibility through the following topics:

1. values and committed action;
2. cognitive defusion;
3. acceptance and willingness;
4. mindfulness and the observing self.

Each module includes animated presentations, YouTube videos, audio recordings, and experiential exercises grounded in ACT principles. To support engagement, participants will receive automated reminders, one supplementary learning activity per module, module summaries upon completion, and invitations to complete

The study includes two assessment pathways (Full research Arm and Minimal research Arm), but these do not constitute separate intervention arms because all participants will receive immediate access to the web-based YOLO program after providing informed consent. The intervention consists of four online modules, each based on the core principles of Acceptance and Commitment Therapy (ACT), and participants will be encouraged to complete one module per week. The program is designed to promote psychological flexibility through the following topics:

1. values and committed action;
2. cognitive defusion;
3. acceptance and willingness;
4. mindfulness and the observing self.

Each module includes animated presentations, YouTube videos, audio recordings, and experiential exercises grounded in ACT principles. To support engagement, participants will receive automated reminders, one supplementary learning activity per module, module summaries upon completion, and invitations to complete.

The Depression Anxiety and Stress Scales 21 (DASS-21) is a 21-item self-report measure assessing three core symptom dimensions of negative emotional states: depression, anxiety, and stress. Each item is rated on a 4-point scale from 0 ("Did not apply to me at all") to 3 ("Applied to me very much, or most of the time"), referring to the past week.

Subscale and total scores are calculated by summing the relevant items. Higher scores indicate greater severity of depression, anxiety, and stress symptoms.

The Mental Health Continuum Short Form (MHC-SF) is a 14-item measure assessing positive mental health across three dimensions: emotional, social, and psychological well-being. Each item is rated on a 6-point frequency scale from 0 ("Never") to 5 ("Every day"), referring to the past month.

Total and subscale scores are calculated by summing or averaging the relevant items. Higher scores indicate greater well-being.

This self-report questionnaire assesses students perceived academic functioning. Items are rated on a 10-point scale from 1 ("Performing at your worst") to 10 ("Performing at your best"), with an additional "Not applicable" option where relevant.

Scores are calculated by averaging the valid items. Higher scores indicate better perceived academic performance and academic functioning. The total score reflects the mean level of perceived academic performance across the retained academic functioning items.

The Satisfaction with Life Scale (SWLS) is a 5-item measure assessing global cognitive judgements of satisfaction with one's life. Each item is rated on a 7-point scale from 1 ("Strongly disagree") to 7 ("Strongly agree").

Total scores are calculated by summing the 5 items, with higher scores indicating greater life satisfaction.

The Acceptance and Action Questionnaire-II (AAQ-II) is a 7-item self-report measure assessing psychological inflexibility and experiential avoidance, reflecting the extent to which individuals are unwilling to experience unwanted thoughts and feelings while pursuing valued actions. Each item is rated on a 7-point Likert scale ranging from 1 ("Never true") to 7 ("Always true").

Total scores are calculated by summing the 7 items, with higher scores indicating greater psychological inflexibility and experiential avoidance.

The Cognitive Fusion Questionnaire (CFQ; Gillanders et al., 2014) is a 7-item self-report measure assessing the extent to which individuals become entangled with, or dominated by, their thoughts and treat them as literal truths. Each item is rated on a 7-point Likert scale ranging from 1 ("Never true") to 7 ("Always true").

Total scores are calculated by summing the 7 items, with higher scores indicating greater cognitive fusion.

The Engaged Living Scale-Short Form (ELS-SF) is a 9-item self-report measure assessing the extent to which individuals live in accordance with their personal values and experience a sense of fulfilment in daily life. The scale includes dimensions of value-consistent action and life fulfilment.

Total scores are calculated by summing or averaging the relevant items, with higher scores indicating greater engaged, value-consistent living.

The Mindful Attention Awareness Scale (MAAS) is a 15-item self-report measure assessing an individual's tendency to attend to and be aware of present-moment experiences in everyday life. Each item is rated on a 6-point Likert scale ranging from 1 ("Almost always") to 6 ("Almost never").

Total scores are calculated by averaging the 15 items, with higher scores indicating greater present-moment awareness and mindfulness.