| | Risk of bias | | Selection of participants | Confounding variables | Measurement of exposure | Blinding of outcome assessments | Incomplete outcome data | Selective outcome reporting |
| | Cohort study | | Kim, 2018 [27] | Low | Low | Low | Low | Low | Unclear | | Teipel, 2018 [31] | Low | Low | Low | Low | Low | Unclear | | Aiello Bowles, 2016 [30] | Low | Low | Unclear | Low | Low | Unclear | | Chen, 2014-1 [26] | Low | Low | Low | Low | Low | Unclear | | Zuo, 2010 [8] | Low | High | Low | Low | Low | Unclear | | Lee, 2005 [9] | Low | Low | Low | Low | Low | Unclear | | Case-control study | | Strand, 2019 [62] | Low | Low | Low | Low | Low | Unclear | | Huang, 2018 [63] | Low | Low | Low | Low | Low | Unclear | | Chen, 2014-2 [25] | Low | Low | Low | Low | Low | Unclear | | Sprung, 2013 [59] | Low | Low | Low | Low | Low | Unclear | | Bufill, 2009 [61] | Low | Low | Unclear | Low | Low | Unclear | | Yip,2006 [28] | Low | Low | Unclear | Low | Low | Unclear | | Harmanci, 2003 [14] | Low | Low | Unclear | Low | Low | Unclear | | Gasparini, 2002 [29] | Unclear | Low | Low | Low | Low | Unclear | | Tyas, 2001 [60] | Low | Low | Unclear | Low | Low | Unclear | | Bohnen 1994 [10] | Low | Low | Low | Low | Low | Unclear | | CHSA, 1994 [57] | Low | Low | Unclear | Low | Low | Unclear | | Li, 1992 [15] | Low | Low | Unclear | Low | Low | Unclear | | Kokmen, 1991 [11] | Low | Low | Low | Low | Low | Unclear | | Graves, 1990 [56] | Low | Low | Unclear | Low | Low | Unclear | | Broe, 1990 [58] | Low | Low | Unclear | Low | Low | Unclear | | Amaducci, 1986 [12] | Low | Low | Unclear | Low | Low | Unclear | | Heyman, 1984 [13] | Low | Low | Unclear | Low | Low | Unclear |
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