Methodologic quality of cohort 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 could be awarded for this item. Studies that controlled for age received 1 star, and studies that controlled for smoking received an additional star. bA cohort study with a follow-up time longer than 5 years was assigned 1 star. cA cohort study with a follow-up rate >70% was assigned 1 star.