Methodologic quality of case-control studies included in the Meta-analysis.

Note: A study can be given a maximum of one star for each item with the Selection and Outcome categories. A maximum of two stars can be awarded for Comparability. (Column 2–5, Selection; Column 6, Comparability; Column 7–9, Outcome). aA maximum of 2 stars awarded for this item. Studies that controlled for age received 1 star, and studies that controlled for other factors received an additional star. b A maximum of 2 stars awarded for this item. Studies that ascertained the exposure with a secure record received 1 star, and studies with structured interview where blind to case/control status received an additional star.