Table 2 Data extraction and synthesis to assess systematic review aims

Intervention efficacy

Type of health behaviour and mental health outcome measures, measurement tools used, measurement timepoints and significance of findings were extracted to determine intervention efficacy.

An intervention was deemed effective if it reported a statistically significant improvement in both health behaviour outcome and mental health outcome.

Intervention impact

The PIPE Impact Metric [67] was utilised to assess intervention impact (penetration, implementation, participation and effect).

• Penetration: the proportion of the target group reached by invitations to engage in the study.

• Implementation: the degree to which the intervention was implemented according to plan (i.e. fidelity). Studies were classified as having low fidelity if no measures of fidelity were reported (e.g., manual, checklist, quality measures including session recordings), moderate fidelity if a manual but no checklist or quality measures were reported and high fidelity if both a manual and checklist or quality measures were reported.

• Participation: the proportion of invited individuals who enrolled in the study and effect was defined as a statistically significant improvement in both health behaviour and mental health outcomes.

Intervention characteristics associated with improved outcomes

Intervention characteristics were assessed according to the Template for Intervention Description and Replication (TIDieR) checklist [68]. Data was extracted to describe the Why (theoretical framework), Who (intervention provider), Where (intervention location), How (mode of delivery and delivery format), When (intervention duration) and How much (number of sessions), Tailoring (e.g. interventions that were personalized), Modification (e.g. interventions that were modified during course of the study) and How Well (retention rates and fidelity). Data collected on intervention provider was classified as health professional, peer, automated delivery or other. Data collected on intervention location was classified as researcher-based (i.e. participant goes to the intervention e.g., at research centre, health care centre etc. within the university), participant-based (i.e. intervention comes to the participant e.g. within their dorm, home etc.) or a combination of both participant-based and research-based. Data collected on mode of delivery was classified as in person, telephone/telehealth or technology-based (excluding telephone/telehealth) while data on delivery format was classified as individual, group or both. The total number of sessions (how much) were calculated based on the different modes of contact used. As defined in previous review, one in-person group or individual session was equivalent to 1 session, one online or telephone session was equivalent to 0.5 session and any contact via text, email, fax or newsletter was equivalent 0.25 session.(72)

To determine intervention characteristics associated with improved outcomes, an effectiveness ratio was calculated by dividing the number of interventions that were effective and used a particular intervention characteristic by the total number of interventions that used that characteristic for each criterion of the TIDieR checklist. These effectiveness ratios are presented as percentages with higher values indicating greater effectiveness of the characteristic. The effectiveness ratios were utilised for comparison of the efficacy of specific intervention characteristics when there were at least three studies featuring each intervention characteristic for each criterion of the TIDieR checklist to ensure reliable comparison.

Economic evaluation

To assess the economic evaluation of interventions, data was collected on whether each study conducted an economic evaluation of their interventions.