Table 3 Summary of methodological quality of included studies
Methodological quality of the randomized controlled trials | Â | ||||||||||
| Â | Was true randomization used for assignment of participants to treatment groups? | Were treatment groups similar at the baseline? | Were outcomes assessors blind to treatment assignment? | Were treatments groups treated identically other than the intervention of interest? | Was follow-up complete, and if not, were strategies to address incomplete follow-up utilized? | Were participants analyzed in the groups to which they were randomized? | Were outcomes measured in the same way for treatment groups? | Were outcomes measured in a reliable way? | Was appropriate statistical analysis used? | Was the trial design appropriate, and any deviations from the standard RCT design accounted for in the conduct and analysis of the trial? | Quality |
 Dinh [30] | + | + | − | + | − | + | + | ? | + | + | Medium |
 Goldie [31] | ? | − | + | + | − | + | + | + | + | + | Medium |
 Jennings [29] | + | + | + | + | + | + | + | + | + | + | High |
Methodological quality of the cohort studies | Â | ||||||||||
| Â | Were the groups similar and recruited from the same population? | Were the exposures measured similarly to assign people to both exposed and unexposed groups? | Were confounding factors identified? | Were strategies to deal with confounding factors stated? | Were the outcomes measured in a valid and reliable way? | Was follow-up complete, and if not, were the reasons to loss to follow-up described and explored? | Were strategies to address incomplete follow-up utilized? | Was appropriate statistical analysis used? | Quality | ||
 Colligan [33] | − | + | + | + | + | + | N.A. | + | High | ||
 David [35] | + | + | + | − | + | − | − | + | Medium | ||
 Hiza [36] | ? | + | + | + | + | ? | ? | + | Medium | ||
 Hoffman [37] | − | + | + | − | + | ? | ? | + | Medium | ||
 Jennings [28] | − | + | + | + | + | ? | ? | + | Medium | ||
 Landsperger [38] | − | + | + | + | + | + | N.A. | + | High | ||
 Moran [39] | + | + | + | − | + | ? | ? | + | Medium | ||
 Morris [40] | + | + | + | − | + | + | N.A. | + | High | ||
 Roche [42] | + | + | + | − | + | ? | ? | + | Medium | ||
 Scherzer [41] | − | + | + | − | + | ? | ? | + | Medium | ||
 Skinner [34] | + | + | − | − | + | ? | ? | + | Medium | ||
 Steiner [32] | ? | + | + | + | + | − | − | + | Medium | ||