Methodological quality assessment
The risk of bias in the selected studies was assessed using an
adaptation of the Cochrane Collaboration’s tool for assessing the risk
of bias (ROB).10 The criteria involved assessing
studies for selection bias caused by random sequence generation and
allocation concealment; performance bias caused by blinding of
participants and personnel; detection bias caused by blinding of outcome
assessment; attrition bias caused by incomplete outcome data; and
reporting bias caused by selective outcome reporting. We assigned a
judgment related to risk of bias by answering a prespecified question
about the adequacy of the study in relation to the entry. A judgment of
”green” indicated a low risk of bias, ”red” indicated a high risk of
bias, and ”yellow” indicated an unclear or unknown risk of bias. The
methodological quality of the included studies was independently
assessed by two researchers (J.H.S. and D.H.L.). Disagreements were
resolved by discussion.