Table 2.

Risk bias of seven retrospective cohort studies.

Author/Year	Confounding	Selection	Interventions Classification	Interventions Deviations	Missing Data	Measurement of Outcomes	Selective Results
Flagas, M.E., 2009 [23]	serious risk	serious risk	serious risk	serious risk	low risk	serious risk	serious risk
Batirel, A., 2014 [24]	serious risk	serious risk	serious risk	serious risk	low risk	serious risk	low risk
Yilmaz, G.R., 2015 [25]	serious risk	serious risk	serious risk	moderate risk	low risk	serious risk	low risk
Park, S.Y., 2019 [27]	serious risk	serious risk	serious risk	serious risk	low risk	serious risk	low risk
Shi, H., 2019 [28]	serious risk	serious risk	serious risk	low risk	low risk	serious risk	low risk
Katip, W., 2020 [31]	serious risk	moderate risk	low risk	low risk	low risk	moderate risk	low risk
Seok, H., 2021 [32]	serious risk	moderate risk	low risk	low risk	low risk	moderate risk	low risk