Table 2: The study quality scores of the studies included in meta-analysis.

First author, year of publication (reference)Objects selectionComparabilityExposure/resultTotal quality scores
Adequate definition/exposed cohort representat-ivenessRepresentativeness of cases/nonexposed cohortControls selection/exposure ascertainmentControls definition/outcome not presentExposure ascertainment/outcome assessmentcases and controls ascertainment method/followup lengthNonresponse rate/adequate followup

Campos, 2006 [12]0 07
Tsugane, 2004 [21] 0 8
Peleteiro, 2011 [11]08
Pourfarzi, 2009 [13]08
Yang, 2011 [17]08
Shikata, 2006 [19]00 7
Ward, 1999 [15]007
Ngoan, 2002 [20]00 7
Ramón et al., 1993 [14]08
Lee, 2003 [16]08
Kim, 2010 [18]0 8