Table 3.

Quality evaluation results of the 2 included CCTs.

Study	Case definition adequacy	Case representativeness	Control selection	Definition of controls	Comparability of cases and controls	Exposure ascertainment	Uses the same method to determine case and control exposure factors	Nonresponse rate	Total
Jin [21]	★			★	★★		★	★	6
Yang [29]	★			★	★★		★	★	6