Table 1

Risk of bias judgments for included studies

StudySequence generationAllocation concealmentBlindingIncomplete outcome dataSelective outcome reportingClusteringOther source of bias
BBBS28 29?+?+
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.