Table 2.

The study quality scores of the studies included in meta-analysis.

First author, year of publication (reference)	Objects selection				Comparability	Exposure/result			Total quality scores
	Adequate definition/exposed cohort representat-iveness	Representativeness of cases/nonexposed cohort	Controls selection/exposure ascertainment	Controls definition/outcome not present		Exposure ascertainment/outcome assessment	cases and controls ascertainment method/followup length	Nonresponse rate/adequate followup
Campos, 2006 [12]	⋆	⋆	0	⋆	⋆  ⋆	⋆	⋆	0	7
Tsugane, 2004 [21]	⋆	⋆	⋆	⋆	⋆  ⋆	⋆	⋆	0	8
Peleteiro, 2011 [11]	⋆	⋆	⋆	⋆	⋆  ⋆	⋆	⋆	0	8
Pourfarzi, 2009 [13]	⋆	⋆	⋆	⋆	⋆  ⋆	⋆	⋆	0	8
Yang, 2011 [17]	⋆	⋆	⋆	⋆	⋆  ⋆	⋆	⋆	0	8
Shikata, 2006 [19]	0	⋆	⋆	⋆	⋆  ⋆	⋆	⋆	0	7
Ward, 1999 [15]	0	⋆	⋆	⋆	⋆  ⋆	⋆	⋆	0	7
Ngoan, 2002 [20]	0	⋆	⋆	⋆	⋆  ⋆	⋆	⋆	0	7
Ramón et al., 1993 [14]	⋆	⋆	⋆	⋆	⋆  ⋆	⋆	⋆	0	8
Lee, 2003 [16]	⋆	⋆	⋆	⋆	⋆  ⋆	⋆	⋆	0	8
Kim, 2010 [18]	⋆	⋆	⋆	⋆	⋆  ⋆	⋆	⋆	0	8