Table 2:

Results of the quality assessment

Author (yr)	Items								Total NOS stars
	Selection				Comparability	Outcome/exposure
Cohort	1	2	3	4	5	6	7	8
Downey (2015)	*	*	*	*	*	*	*		*******
Ginsberg (2019)	*	*	*	*	**	*	*	*	*********
Gustavson (2019)	*	*		*	**	*	*	*	********
Mann (2011)	*	*	*	*	**	*	*		********
Werenberg Dreier (2016)	*	*		*	**	*	*		*******
Case controls
Oerlemans (2016)	*	*	*	*	**	*	*		********
Pineda (2007)	*	*	*	*	**		*		*******
Silva (2014)	*	*	*	*	**	*	*	*	*********
Arpino (2005)	*	*	*	*	*		*		******
Chudal (2019)	*	*	*	*	**	*	*		********
Cross sectional studies
Afsharpaiman (2016)				**	*	*			****
Mellins (2009)		*		*	**	*	*		******
Schmitt (2012)	*	*		*	**	**	*		********

Cohort studies: 1. Representativeness of the exposed cohort, 2. Selection of the non-exposed cohort, 3. Ascertainment of exposure, 4. Demonstration that outcome of interest was not present at start of study, 5. Comparability of cohorts on the basis of the design or analysis controlled for confounders, 6. Assessment of outcome, 7. Was follow-up long enough for outcomes to occur, 8. Adequacy of follow up of cohorts

Case control studies: 1.Is the case definition adequate?, 2. Representativeness of the cases, 3. Selection of Controls, 4. Definition of Controls, 5. Comparability of cases and controls on the basis of the design or analysis, 6. Ascertainment of exposure, 7. Same method of ascertainment for cases and controls, 8. Non-Response rate

Cross sectional studies: 1. Representativeness of the sample, 2. Sample size, 3. Non-respondents, 4. Ascertainment of the exposure (risk factor), 5. The subjects in different outcome groups are comparable, based on the study design or analysis, 6. Assessment of the outcome, 7. Statistical test