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).