Risk of bias judgments for included studies
| Study | Sequence generation | Allocation concealment | Blinding | Incomplete outcome data | Selective outcome reporting | Clustering | Other source of bias |
|---|---|---|---|---|---|---|---|
| BBBS28 29 | ? | + | − | − | ? | − | + |
| NGYCP36–38 | ? | ? | ? | + | ? | + | + |
| QOP30 31 | ? | ? | − | + | ? | + | + |
+, low risk of bias; −, high risk of bias; ?, unclear risk of bias.
BBBS, Big Brothers Big Sisters; NGYCP, National Guard Youth ChalleNGe Program; QOP, Quantum Opportunity Project.