Summary of Quality Assessments.

1<p>Maximum of 4 stars for: representativeness of the exposed cohort; selection of the non-exposed cohort; ascertainment of exposure; and demonstration that outcome of interest was not present at start of study.</p>2<p>Maximum of 2 stars for: comparability of cohorts on the basis of the design or analysis.</p>3<p>Maximum of 3 stars for: assessment of outcome; was follow-up long enough for outcome to occur; and adequacy of follow-up of cohorts.</p><p>NR not reported.