Table 3.

Riskof Bias Assessment: summarizing the quality assessment results of each study using the Newcastle-Ottawa scale, categorizing them by risk level

Study ID	Hohmann et al. [27]	Wall et al. [31]	Benito-González et al. [28]	Suri et al. [9]	Paparella et al. [23]	Körber et al. [26]	Waechter et al. [29]	Noohi et al. [36]	Valeur et al. [20]	Watt et al. [32]	Seeger et al. [22]	Meurin et al. [25]
Sample selection criteria (****)	****	****	****	****	****	****	****	****	****	****	****	****
1) Representativeness of the exposed cohort (a) Truly representative (one star) (b) Somewhat representative (one star) (c) Selected group (d) No description of the derivation of the cohort	*	*	*	*	*	*	*	*	*	*	*	*
2) Selection of the non-exposed cohort (a) Drawn from the same community as the exposed cohort (one star) (b) Drawn from a different source (c) No description of the derivation of the non-exposed cohort	*			*	*		*	*	*	*	*
3) Ascertainment of exposure (a) Secure record (e.g., surgical record) (one star) (b) Structured interview (one star) (c) Written self-report (d) No description (e) Other	*	*	*		*		*	*		*		*
4) Demonstration that outcome of interest was not present at start of study (a) Yes (one star) (b) No	*	*	*	*	*	*	*	*	*	*	*	*
Comparability (**)	**	**	**	**	**	**	**	**	**	**	**	**
1) Comparability of cohorts on the basis of the design or analysis controlled for confounders (a) The study controls for age, sex and marital status (one star) (b) Study controls for other factors (list) (one star) (c) Cohorts are not comparable on the basis of the design or analysis controlled for confounders	*	**	**	*	**	**	**	**		*		**
Exposure (***)	***	***	***	***	***	***	***	***	***	***	***	***
1) Assessment of outcome (a) Independent blind assessment (one star) (b) Record linkage (one star) (c) Self report (d) No description (e) Other	*	*		*	*	*	*	*		*		*
2) Was follow-up long enough for outcomes to occur (a) Yes (one star) (b) No	*	*	*		*	*	*	*	*	*	*	*
3) Adequacy of follow-up of cohorts (a) Complete follow up- all subject accounted for (one star) (b) Subjects lost to follow up unlikely to introduce bias- number lost less than or equal to 20% or description of those lost suggested no different from those followed. (one star) (c) Follow up rate less than 80% and no description of those lost (d) No statement		*	*				*		*		*
Summary quality score	Good	Good	Good	Poor	Good	Fair	Good	Good	Poor	Good	Poor	Good
ID, identification Score: Good quality: 3 or 4 stars in selection domain AND 1 or 2 stars in comparability domain AND 2 or 3 stars in outcome/exposure domain Fair quality: 2 stars in selection domain AND 1 or 2 stars in comparability domain AND 2 or 3 stars in outcome/exposure domain Poor quality: 0 or 1 star in selection domain OR 0 stars in comparability domain OR 0 or 1 stars in outcome/exposure domain