Table 4.

Risk of bias in non-randomized studies

Study	Confounding	Selection bias	Classification of intervention	Deviation from intervention	Missing data	Outcome measurement	Selection of reported results	Overall risk of bias
Swedish et al. 2012 [25]a	+	–	++	++	–	++	++	–
Swedish and Goldstone 2014 [34]a	+	–	++	++	–	++	++	–
Kahn et al. [24]b	– –	–	–	++	–	++	++	– –

++ low risk of bias, + moderate risk of bias, − serious risk of bias, – –- critical risk of bias

^aUnclear selection into study; differences in follow-up time between groups; loss-to-follow up

^bOnly unadjusted data available; unclear selection into study; loss-to-follow up; possible misclassification of intervention