Table 2: Risk of bias within studies.

Wigers et al. 1996Jones et al. 2002 Richards and Scott 2002Rooks et al. 2007Bircan et al. 2008Duruturk et al. 2015García-Martínez et al. 2012Gavi et al. 2014Hooten et al. 2012Kayo et al. 2012Larsson et al. 2015Mannerkorpi et al. 2010Sañudo et al. 2010Sañudo et al. 2011Ericson et al. 2016

Random sequence generationLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow risk
Allocation concealmentLow riskLow riskLow riskLow riskRisk unclearLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow risk
Blinding of participants and personnelHigh riskHigh riskHigh riskHigh riskHigh riskHigh riskHigh riskHigh riskHigh riskHigh riskHigh riskHigh riskHigh riskHigh riskHigh risk
Blinding of outcome assessmentRisk unclearLow riskLow riskRisk unclearRisk unclearLow riskRisk unclearLow riskHigh riskRisk unclearLow riskLow riskLow riskLow riskLow risk
Incomplete outcome dataLow riskHigh riskLow riskLow riskHigh riskLow riskHigh riskHigh riskLow riskLow riskLow riskLow riskLow riskLow riskLow risk
Selective reportingLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow risk
Other biasLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow riskLow risk