Table 3.

Newcastle-Ottawa Scale Risk of Bias of Included Observational Studies

	Representativeness of the Sample	Sample Size	Non-Respondents	Ascertainment of the Exposure (Risk Factor)	Comparability:	Assessment of the Outcome	Statistical Test		Total
Dale-Perera 2015	*	0	*	0	*	*	*		5
Stover 2010	*	0	0	**	*	*	*		6
	Representativeness of the exposed cohort	Selection of the non-exposed cohort	Ascertainment of the exposure (risk factor)	Demonstration that the outcome of interest was not present at beginning of study	Comparability:	Assessment of the outcome	Was the follow-up long enough for outcomes to occur	Adequacy of follow-up of cohorts	Total
Groshkova 2013	*	*	*	*	*	0	*	0	6

Notes: *Indicates one star in the NOS scale. **Indicates two stars in the NOS.