Table 2.

Risk of bias assessment of studies included in meta-analysis

Study	N	Study type	Fulfilled criteria/overall number of criteria	Overall appraisal	Unclear/not-fulfilled criteria
Chiu et al. (2017) [39]	97	Observational cohort	8 out of 11	Included	- Not applicable: 3 questions regarding follow-up
Ginting et al. (2010) [40]	96	Cross sectional	6 out of 8	Included	- Unclear: information on confounding factors and strategies regarding confounding factors
Lai et al. (2015) [41]	233	Observational cohort	6 out of 11	Included	- Unclear: information on confounding factors and strategies regarding confounding factors - not applicable: 3 questions regarding follow-up
Muere et al. (2017) [42]	341	Cross sectional	8 out of 8	Included
Nickel et al. (2010) [43]	207	Case control	9 out of 10	Included	- Unclear: strategies regarding confounding factor
Tripp et al. (2016) [44]	190	Case control	10 out of 10	Included
Watkins et al. (2011) [34]	1469	Observational cohort	6 out of 11	Included	- Unclear: information on confounding factors and strategies regarding confounding factors - not applicable: 3 questions regarding follow-up

Notes: N = number of participants; case control studies were evaluated with the Joanna Briggs Institute (JBI) Critical Appraisal Checklist for Case Control Studies (10 criteria); cross-sectional studies are evaluated with the JBI Critical Appraisal Checklist for Analytical Cross Sectional Studies (8 criteria); observational cohort studies were evaluated with the JBI Critical Appraisal Checklist for Cohort Studies (11 criteria) [37]