Table 2.

Detailed summary of critical appraisal of included studies using the Newcastle Ottawa Scale (NOS) for assessing the quality of non-randomised control trials (cross-sectional/cohort and case–control studies)

Study, country	NOS quality assessment for studies included (cross-sectional studies/cohort studies)
	Selection				Comparability	Outcome
	Representativeness of the sample	Selection of the non-exposed cohort	Ascertainment of exposure	Demonstration that outcome of interest was not present at study start	Comparability of the groups on the basis of design or analysis	Assessment of outcome	Adequacy of follow-up of cohorts	Was follow-up long enough for outcomes to occur	Overall quality assessment score (maximum of 9)	Quality (high, medium, low)
Applegate et al66 USA n=1226	*	*	*		**				5	Medium quality
Rechardt et al42 Finland n=6237	*	*	*		*	*			5	Medium quality
Rechardt et al43 Finland n=163	*	*	*		*	*			5	Medium quality
Judge et al68 France n=147			*						1	Low quality

	NOS quality assessment for studies included (case–control studies)
	Selection				Comparability	Exposure
	Is the case definition adequate?	Representativeness of the cases	Selection of controls	Definition of controls	Comparability of cases or controls on the basis of design or analysis	Ascertainment of exposure	Same method of ascertainment for cases and controls	Non-Response rate
Abate et al55 Italy n=180	*		*	*	*	*	*	6	Medium quality
Djerbi et al67 France n=306	*	*	*	*	**	*	*	*	9	High quality

NOS, The Newcastle Ottawa Scale for assessing the quality of non-randomised control trials (cross-sectional/cohort and case–control studies).

* and ** are the star rating as per NOS with the study satisfying the item. A study can be awarded a maximum of one star for each numbered item within the Selection and Exposure categories. A maximum of two can be given for Comparability.