Table 3

Study quality: reporting and risk of bias summary (Downs and Black27)

Study lead author, dateReporting score n/11External validity score n/3Internal validity—bias score n/7Internal validity—confounding score n/6Power score n/1Total score n/28Quality level*
Ferrell, 1995412007Poor
Wells, 20036142013Poor
Keefe, 20059335020Good
Lin, 20066132012Poor
Ward, 20098254120Good
Capewell, 20106121010Poor
Vallerand, 20105132011Poor
Valeberg, 20136132012Poor
  • *Based on Samoocha et al's28 classification of quality level: excellent (26–28); good (20–25); fair (15–19); poor (≤14).