Table 3.

Quality evaluation of cohort and case-control study.

Author	Study population selection	Intergroup comparability	Outcome measurement	total points
Butland 1997[22]	☆☆☆	☆☆	☆☆	7
Austin 1997[18]	☆☆☆	☆	☆☆	6
Magnusson 2005[23]	☆☆☆☆	☆☆	☆	7
Johansson 2007[21]	☆☆☆☆	☆☆	☆☆☆	8
Thacher 2014[19]	☆☆☆☆	☆☆	☆☆	8
Liao 2015[17]	☆☆☆	☆☆	☆	6
Patil2015[13]	☆☆☆☆	☆☆	☆☆☆	9
Mitselou 2020[12]	☆☆☆	☆☆	☆☆	7

The New Castle–Ottawa scale (NOS): a scale for assessing the quality of published non-randomized studies in meta-analyses.