Table 2. Quality assessment of included studies based on the newcastle–ottawa scale.

Study	Selection (score)				Comparability (score)	Exposure (score)			Total scoreb
	Adequate definition of patient case	Representativeness of patients cases	Selection of controls	Definition of control	Control for important factor or additional factor	Ascertainment of exposure (blinding)	Same method of ascertainment for participants	Non-response ratea
He BS [11]	1	1	1	1	2	0	1	0	7
Du ML [12]	1	1	1	1	2	0	1	0	7
Dikeakos P [13]	1	1	0	1	2	0	1	1	7
Wei WJ [15]	1	1	1	1	2	0	1	0	7
Wang R [16]	1	1	0	1	1	0	1	0	5
Huang GL [18]	1	1	1	1	2	0	1	0	7
Song XC [21]	1	1	1	1	2	0	1	1	8
Tu HF [22]	1	1	0	1	2	0	1	0	6
Zhang M [23]	1	1	1	1	2	0	1	0	7
Zhang MW [24]	1	1	1	1	2	0	1	0	7
Min KT [25]	1	1	1	1	2	0	1	0	7
Aho DH [26]	1	1	1	1	2	0	1	1	8
Kim WH [27]	1	1	1	1	2	0	1	0	7
Vinci S [28]	1	1	1	1	1	0	1	0	6
Vinci S [29]	1	1	0	1	2	0	1	0	7
Li PY [30]	1	1	0	1	2	0	1	0	6
Zhang MW [31]	1	1	1	1	2	0	1	0	7
Liu ZS [32]	1	1	1	1	2	0	1	1	8
Tian T [33]	1	1	1	1	2	0	1	0	7
Wang ZW [34]	1	1	1	1	1	0	1	0	6
Qi P [36]	1	1	1	1	2	0	1	0	7
Yin ZH [37]	1	1	0	1	2	0	1	0	6
Cao Y [38]	1	1	1	1	2	0	1	0	7
Kupcinskas J (C) [39]	1	1	0	1	0	0	1	0	4
Kupcinskas J (G) [40]	1	1	0	1	2	0	1	0	6
Song B [41]	1	1	1	1	2	0	1	0	7
Zhang JJ [42]	1	1	1	1	2	0	1	0	7
Zhang N [43]	1	1	1	1	2	0	1	0	7
Catucci I [44]	1	1	0	1	1	0	1	0	5
Hezova R [45]	1	1	1	1	1	0	1	0	6
Shi DN [46]	1	1	1	1	2	0	1	0	7
Zhang MW [47]	1	1	1	1	0	0	1	0	5
Zhou Y [49]	1	1	0	1	1	0	1	0	5
Zhang P [50]	1	1	1	1	1	0	1	0	6
Sun QM [51]	1	1	0	1	2	0	1	0	6
Kontorovich T [52]	1	1	1	1	0	0	1	0	5
Yang RX [53]	1	1	1	1	2	0	1	0	7

^aWhen there was no statistical significance in the response rate between case and control groups by using a chi-squared test (P > 0.05), one point was awarded.

^bTotal score was calculated by adding up the points awarded in each item.