Risk of bias assessment across individual studies
Each study was assessed for risk of bias by two review authors
independently. The Cochrane Collaboration’s tool for assessing risk of
bias comprises a description and a judgment for the following criteria:
random sequence generation, allocation concealment, blinding of
participants and personnel, blinding of outcome assessment, incomplete
outcome data, selective reporting and other sources of bias. Each
criterion was judged ’low risk of bias’, ’high risk of bias’, or
’unclear risk of bias. This review is not registered.