Table 7.

Risk of Bias assessment tool (based on QUIPS, Hayden et al. [13])

Domain	Items
1. Study participation	1a. Method used to identify population: recruitment of participants for the study was performed in a consecutive way 1b. Adequate study participation: at least 70% of recruited individuals agreed to participate
2. Study attrition	2a. Adequate follow-up rate: at least 80% of the baseline study participants participated at follow-up 2b. There are no important differences between participants who completed the study and those who did not
3. Determinant measurement	3a. Adequate proportion of complete data: at least 70% of the study sample has complete data on the determinant(s) 3b. The method and setting of determinant measurement is the same for all study participants 3c. Appropriate methods of imputation are used for missing determinant data
4. Outcome measurement	4a. Outcome measure truly captures participation in voluntary work and does not allow for participation in informal caregiving or other productive activities not equal to volunteering, unless subgroups are made for the distinct forms of participation 4b. The method and setting of outcome measurement is the same for all study participants
5. Study confounding	5a. The following potentially important confounders are measured: a1. age a2. socioeconomic status (e.g. education, income) a3. gender a4. participation in voluntary work at baseline 5b. The method and setting of measurement of the confounders is the same for all study participants 5c. Appropriate methods of imputation are used for missing data regarding the confounders 5d. The following potentially important confounders are accounted for in the study design (e.g., matching for key variables, stratification, or initial assembly of comparable groups) or in the analysis (i.e., appropriate adjustment) d1. age d2. socioeconomic status (e.g. education, income) d3. gender d4. participation in voluntary work at baseline
6. Statistical analysis and reporting	6a. The selected statistical model is adequate for the design of the study design 6b. There is no over fitting (at least 10 participants in the smallest group per determinant and outcome variable) 6c. There is no selective reporting of results