Table 2.

Co-variables collected in the selected studies (candidates for a potential effect measure modification assessment).

Study	Age	Sex	Socio-Economic Factors *	Urbanization Level	Smoking	Other Health Behaviors
Wilkins and Comstock 1981 [51]	X	X	X		X
Gottlieb and Carr 1982 [65]	X	X
Zierler et al. 1988 [55]				X	X
McGeehin et al. 1993 [53]					X
King and Marrett 1996 [67]	X	X	X		X
Freedman et al. 1997 [54]	X		X	X
Koivusalo et al. 1997 [52]	X	X	X	X	X
Cantor et al. 1998 [64]	X	X	X		X
Hildesheim et al. 1998 [66]				X		X
Koivusalo et al. 1998 [56]	X	X	X	X	X
King et al. 2000 [57]	X	X	X			X
Chevrier et al. 2004 [58]	X		X	X	X
Bove et al. 2007 [63]	X		X			X
Bove et al. 2007 [59]	X				X	X
Chang et al. 2007 [60]	X			X
Michaud et al. 2007 [61]	X	X	X
Villanueva et al. 2007 [68]	X	X	X	X	X
Kuo et al. 2009 [69]	X	X		X
Cantor et al. 2010 [62]	X	X	X		X

* Include education, occupation status, or SES index.