TABLE 2.

Risk of bias assessment for selected studies.

		Dion et al. (2004)	Awaisu et al. (2012)	Kittikraisak et al. (2012)	Kastien-Hilka et al. (2017)	Saleem et al. (2018)	Zarova et al. (2018)	Shedrawy et al. (2019)
Risk of bias assessment tool for non-randomized study (RoBANS)
Selection of participants		Low	Low	Low	Low	Low	Low	Low
Confounding variables		Unclear	Unclear	Unclear	Unclear	Unclear	Unclear	Unclear
Intervention measurement		Low	Low	Low	Low	Low	Low	Low
Blinding of outcome assessment		High	High	High	High	High	High	High
Incomplete outcome data		Low	Low	Low	Low	Low	Low	Low
Selective outcome reporting		Low	Low	Low	Low	Low	Low	Low
Newcastle-ottawa quality assessment scale (NOS)
Selection	Representativeness of the exposed cohort	*	*	*	*	*	NA	NA
	Selection of the non-exposed cohort	-	-	-	-	-	NA	NA
	Ascertainment of exposure	*	*	*	*	*	NA	NA
	Outcome of interest was not present at start of study	*	*	*	*	*	NA	NA
Comparability	Comparability of cohorts on the basis of the design	*	*	*	*	*	NA	NA
Exposure	Assessment of outcome	-	-	-	-	-	NA	NA
	Enough follow-up for outcomes to occur	*	*	*	*	*	NA	NA
	Non-response rate	*	*	*	*	*	NA	NA
NOS Score	Total stars (max 9)	6	6	6	6	6	NA	NA