Table 3. ROBINS-I risk of bias summary: Review authors’ judgements about each risk of bias domain for each included study.

Studies	Bias due to confounding	Bias in selection of participants into the study	Bias in measurement of interventions	Bias due to departures from intended interventions	Bias due to missing data	Bias in measurement of outcomes	Bias in selection of the reported result
Wu et al 2004 [39]	Y	N	N	U	U	Y	N
Zhang et al 2013 [38]	Y	Y	N	N	N	N	N
Lau et al 2004 [42]	N	Y	N	Y	N	Y	N
Ram PK et al 2015 [44]	Y	N	N	N	Y	N	Y
Doshi et al 2015 [43]	N	N	N	N	N	N	N
Flasche et al (2011) [48]	U	U	U	U	U	U	U
Petrovic et al (2011) [50]	U	U	U	U	U	U	U
Chieochansin et al (2009) [46]	U	U	U	U	U	U	U
Rajatonirina et al (2011) [51]	U	U	U	U	U	U	U
Echevarria-Zuno et al (2009) [55]	U	U	U	U	U	U	U
Chowell et al (2011a) [47]	U	U	U	U	U	U	U
Tinoco et al (2009) [52]	U	U	U	U	U	U	U
Chowell et al (2011b) [53]	U	U	U	U	U	U	U
Herrera-Valdez et al (2011) [49]	U	U	U	U	U	U	U

Table 3 shows assessment of risk of bias for the observational studies