Table 3.

Assessment of the quality of studies included in the systematic review.

Study	Selection				Comparability	Outcome			Result
	Representativeness of the exposed cohort	Selection of the non exposed cohort	Ascertainment of exposure	Demonstration that outcome of interest was not present at start of study	Comparability of cohorts on the basis of the design or analysis	Assessment of outcome	Was follow-up long enough for outcomes to occur	Adequacy of follow up of cohorts	Score
Doyen et al. [6]	*	*	*	*	*	*	*	*	8
Randhawa et al. [9]	*	*	*	*	*	*	*	*	8
Frohlich et al. [10]	*	*	*	*	*	*	*	*	8
Budnik et al. [11]	*	*	*	*	*	*	*	*	8
Santoro et al. [12]	*	*	*	*	*	*	*	*	8
Pirzer et al. [14]	*	*	*	*	*	*	*	*	8
Nguyen et al. [19]	*	*	*	*	*	*	*	*	8
Jaguszewski et al. [22]	*	*	*	*	*	*	*	*	8
Hojagergaard et al. [23]	*	*	*	*	*	*	*	*	8
Budnik et al. [24]	*	*	*	*	*	*	*	*	8
Pirlet et al. [36]	*	*	*	*	*	*	*	*	8
Stiermaier et al. [37]	*	*	*	*	*	*	*	*	8