Table 2.

Newcastle-Ottawa quality assessment of observational studies.

First author, year	Study design	Selectiona	Comparabilityb	Outcomec	Total score	Result
Asadi-Pooya AA et al. [21] 2021	Case-control	***	**	**	7	Good
Cabezudo-Garcia P et al. [22] 2020	Cohort	***	**	**	7	Good
Chou SHY et al. [23] 2021	Cohort	****	**	***	9	Good
Clift AK et al. [24] 2020	Cohort	****	**	***	9	Good
Garcia-Azorin D et al. [25] 2021	Cohort	***	**	***	8	Good
Ghaffari M et al. [26] 2021	Cohort	***	**	**	7	Good
Ji W et al. [27] 2020	Case-control	***	**	***	8	Good
Poblador-Plou B et al. [28] 2020	Cohort	***	**	***	8	Good
Romero-Sanchez CM et al. [30] 2020	Cohort	***	**	***	8	Good
Tyson B et al. [31] 2021	Case-control	***	**	***	8	Good
Yin R et al. [32] 2020	Cohort	***	**	***	8	Good

^a(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.

^b(1) comparability of cohorts on the basis of design or analysis, (maximum two stars).

^c(1) assessment of outcome; (2) was follow-up long enough for outcomes to occur; (3) adequacy of follow-up of cohorts.