Table 2. The methodological quality of included studies.
| First author | Year of publication | Adequate definition of cases | Representativeness of cases | Selection of control | Definition of control | Control for important factor or additional factor | Exposure assessment | Same method of ascertainment for cases and controls | Nonresponse rate | Total quality scores |
|---|---|---|---|---|---|---|---|---|---|---|
| Niloofar Khodabandehlou | 2019 | 1 | 1 | 0 | 1 | 2 | 0 | 1 | 0 | 6 |
| Amal ElAmrani | 2018 | 1 | 1 | 0 | 1 | 2 | 0 | 1 | 0 | 6 |
| Jose´ Roosevelt Cavalcante | 2018 | 1 | 1 | 0 | 1 | 2 | 0 | 1 | 0 | 6 |
| Afsaneh Sigaroodi | 2012 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 5 |
| Marla Ladera | 2017 | 1 | 1 | 0 | 1 | 2 | 0 | 1 | 0 | 6 |
| Andrea P.S. Damin | 2004 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 5 |
| B Heng | 2009 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 5 |
| Silvia Delgado-García | 2017 | 1 | 1 | 0 | 1 | 2 | 0 | 1 | 0 | 6 |
| Depu Wang | 2016 | 1 | 1 | 0 | 1 | 2 | 0 | 1 | 0 | 6 |
| Choi, Yoon-La | 2007 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 5 |
| Nan Zhang | 2016 | 1 | 1 | 0 | 1 | 2 | 0 | 1 | 0 | 6 |
| Jie Li | 2015 | 1 | 1 | 0 | 1 | 2 | 0 | 1 | 0 | 6 |
| Ling Fu | 2015 | 1 | 1 | 0 | 1 | 2 | 0 | 1 | 0 | 6 |
| Chun-ling FAN | 2008 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 5 |
| Junping Peng | 2014 | 1 | 1 | 0 | 1 | 2 | 0 | 1 | 0 | 6 |
| Frega, A | 2012 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 5 |
| Liang Hong | 2014 | 1 | 1 | 0 | 1 | 2 | 0 | 1 | 0 | 6 |
| Gumus, M | 2006 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 5 |
| Leila Manzouri | 2014 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 5 |
| Mahin Ahangar-Oskouee | 2014 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 5 |
| Masoud Doosti | 2016 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 5 |
| Nadia Aziz Salman | 2017 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 5 |
| Peng Chang | 2012 | 1 | 1 | 0 | 1 | 2 | 0 | 1 | 0 | 6 |
| Orla M. Gannon | 2015 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 5 |
| Wendy K. Glenn | 2012 | 1 | 1 | 0 | 1 | 2 | 0 | 1 | 0 | 6 |
| Reza Malekpour Afshar | 2018 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 5 |
| S.H.M. Ali | 2014 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 5 |
| de León, D. C. | 2009 | 1 | 1 | 0 | 1 | 2 | 0 | 1 | 0 | 6 |
| Mendizabal-Ruiz, A. P. | 2009 | 1 | 1 | 0 | 1 | 2 | 0 | 1 | 0 | 6 |
| Qian He | 2009 | 1 | 1 | 0 | 1 | 2 | 0 | 1 | 0 | 6 |
| Saimul Islam | 2017 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 5 |
| Smaroula N. Divani | 2012 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 5 |
| Tsai, Ju-Hsin | 2007 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 5 |
| Weili Liang | 2013 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 5 |
| X MOU | 2011 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 5 |
| Yu,Y | 1999 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 5 |
| Zhanping Ren | 2003 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 5 |