Table 2.

The risk of bias in the included studies as assessed using the National Institutes of Health Study Quality Assessment Tool for Observational Cohort and Cross-sectional studies [15].

Author (Year)	Clear Research Question	Population Specified and Defined	Participation Rate of Eligible Persons >50%	All Subjects Similar Populations	Sample Size Justification	Exposure (s) of Interest Measured Prior to the Outcome (s)	Timeframe Sufficient to See Association	Did the Study Examine Different Levels of Exposure?	Exposure Measures Clearly Defined, Valid, Reliable, Implemented Consistently	Exposure Assessed More than Once	Outcome Measures Clearly Defined, Valid, Reliable, Implemented Consistently	Outcome Assessors Blinded to Exposure Status of Participants	Loss to Follow-Up <20%	Confounding Variables Measured and Adjusted Statistically	Quality Rating (Good, Fair, Poor)
Avnon and Anbar [24]	Yes	Yes	NR	Yes	Yes	Yes	Yes	NA	Yes	No	Yes	NR	NR	No	Good
Avnon and Dubinsky [25]	Yes	Yes	NR	Yes	NR	Yes	Yes	NA	Yes	No	Yes	NR	NR	Yes	Poor
Ferrara [27]	Yes	Yes	NR	Yes	NR	Yes	Yes	NA	Yes	No	Yes	NR	NR	No	Poor
Hedegaard [28]	Yes	Yes	No	Yes	NR	Yes	Yes	NA	Yes	No	Yes	NR	NR	Yes	Fair
Kesary [26]	Yes	Yes	NR	Yes	NR	Yes	Yes	NA	Yes	No	Yes	NR	NR	Yes	Fair
Pawlak [29]	Yes	Yes	NR	No	NR	Yes	Yes	NA	Yes	No	Yes	NR	NR	No	Poor

NA = not applicable; NR = not reported.