The quality and level of evidence of the studies were
assessed using Polit and Beck’s hierarchy of evidence
(2008) and the Scottish Intercollegiate Guidelines Network
(SIGN) critical appraisal checklist ( Scottish Intercollegiate,
2012). The 24 articles included: four clustered-randomized
controlled trials at evidence hierarchy level II, 13 non-randomized controlled trials at evidence hierarchy level II,
five single-group pre-posttest studies at evidence hierar-chy level II, and two correlational studies at level IV. The
strengths and limitations of studies evaluated by the
critical appraisal checklist are summarized in Tables