Table 2.

Quality assessment of the included studies

Included studies	Selection				Comparability	Outcome			Total quality scores
	Representativeness of the exposed cohort	Selection of the non-exposed cohort	Ascertainment of exposure	Demonstration that outcome of interest was not present at start of study		Assessment of outcome	Was follow- up long enough for outcomes to occur	Adequacy of follow-up of cohorts
Demirdag et al. 2021[28]	★	★	★		★★	★	★	★	8
Mitter et al. 2021[27]	★	★	★			★	★	★	6
Li et al. 2021[26]		★	★		★	★	★	★	6
Yang et al. 2020[25]	★	★	★		★★	★	★	★	8
Zhang et al. 2019[20]	★	★	★		★★	★	★	★	8
Kitaya et al. 2017[19]	★	★	★		★★	★	★	★	8
Cicinelli et al. 2015[24]	★	★	★		★	★		★	6
Tersoglio et al. 2015[21]			★		★	★	★	★	5
Yang et al. 2014[23]	★	★	★		★	★	★	★	7
Johnston-MacAnanny et al. 2010[22]	★	★	★		★	★		★	6

A study can be awarded a maximum of one star for each numbered item within the Selection and Outcome categories. A maximum of two stars can be given for comparability. A study that has five or more total quality scores is considered moderate quality, and a study that has eight or more total quality scores is considered high quality