Table 2.

Risk of bias assessment summary: Review authors' judgments about each methodological quality item for each included study

Study	Bias arising from the randomization process	Bias from deviations from intended interventions	Bias due to missing outcome data	Bias in measurement of the outcome	Bias in selection of the reported result	Overalla
Goel et al., 2009 28	Some concerns	Low	Low	Low	Some concerns	Some concerns
Jørgensen et al., 2002 29	Some concerns	Some concerns	Low	Low	Some concerns	Some concerns
Kock et al., 199530	Some concerns	Some concerns	Low	High	Some concerns	High
Kujath et al., 1993 31	Some concerns	Some concerns	Some concerns	High	Some concerns	High
Lapidus et al., 2007a 32	Some concerns	Low	Low	Low	Some concerns	Some concerns
Lapidus et al., 2007b 33	Some concerns	Low	Low	Low	Some concerns	Some concerns
Lassen et al., 2002 34	Some concerns	Low	Low	Low	Some concerns	Some concerns
Selby et al., 2015 8	Low	Low	Low	Low	Some concerns	Some concerns
van Adrichem et al., 2017 36	Low	Some concerns	Low	Low	Low	Some concerns
Zheng et al., 2017 6	Some concerns	Low	Some concerns	Low	Some concerns	Some concerns
Gehling et al., 1998 27	Some concerns	Some concerns	Some concerns	High	Some concerns	High
Bruntink et al., 2017 9	Low	Some concerns	Low	Low	Some concerns	Some concerns
Samama et al., 2013 35	Low	Some concerns	Low	Low	Some concerns	Some concerns

^aOverall risk of bias judgment (equal to the most severe level of bias found in any domain) was judged as: 1) Low risk of bias: the study is judged to be at low risk of bias for all domains for this result; 2) Some concerns: the study is judged to have some concerns of bias in at least one domain for this result; 3) High risk of bias: the study is judged to be at high risk of bias in at least one domain for this result or have some concerns for multiple domains in a way that substantially lowers confidence in the result.