Quality assessment of studies
The quality of the studies was assessed with the Newcastle Ottawa scale (University of Ottawa, Ottawa, Ontario, Canada) using the appropriate forms for cohort studies (prospective/retrospective), cross-sectional and case-control studies (23). For ranking the adequacy of follow-up, we awarded one star to studies with the follow-up rate ≥70% or description of those lost suggesting no difference from those followed. We considered high-quality studies those ones with a total score ≥7 stars since standardized criteria for conversion have not been universally established(24, 25).