Table 4.

Quality assessment for 15 randomized controlled trials

Author	Selection				Comparability		Exposure			Total
	Case definition	Representativeness of case	Selection of controls	Definition of controls	Main factors	Additional factors	Ascertainment of exposure	Same method for cases and controls	Non-response rate
Khan [33]	*	*	*	*	*	*	*	*	0	8
Najafizade, Hemati [45]	*	*	*	*	*	0	*	*	0	7
Lyckholm [37]	*	*	*	*	*	*	*	*	0	8
Rojas, Carrasco [27]	*	*	0	0	*	*	*	*	0	6
Ruz, Carrasco [21]	*	*	0	0	*	*	*	*	0	6
Sakagami [39]	*	*	*	*	*	*	*	*	0	8
Ikeda [40]	*	*	0	0	*	*	*	0	0	5
Stewart-Knox, Simpson [44]	*	0	*	*	*	0	*	*	0	6
Halyard, Jatoi [36]	*	*	*	*	*	*	*	*	*	9
Heckmann, Hujoel [42]	*	*	*	*	*	*	*	*	0	8
Sakai [35]	*	*	*	*	*	0	*	*	0	7
Ripamonti [34]	*	*	*	*	*	*	*	*	0	8
Mahajan, Prasad [38]	*	*	*	*	*	0	*	*	0	7
Atkin-Thor, Goddard [43]	*	*	*	*	*	*	*	*	0	8
Henkin, Schecter [41]	*	*	*	*	*	*	*	*	0	8