Table 4. Risk of bias assessment.

The risk of bias assessments was performed using the Newcastle-Ottawa Scale Risk of Bias Assessment tool [23].

	Patel, et al. [29]	Silk, et al. [30]	Mathew, et al. [31]	Knisely, et al. [32]
Representativeness of exposed cohort
Selection of non-exposed cohort
Ascertainment of  exposure	*	*	*	*
Outcome of  interest not present at start of study
Comparability (max 2)	* *	* *		* *
Assessment of outcome	*	*	*	*
Adequacy of follow-up duration	*	*	*	*
Adequacy of follow-up completeness	*	*	*	*
Total score (max 9)	6/9	6/9	4/9	6/9