Results of quality assessment by Newcastle-Ottawa Scale.

Note: For case-control studies, 1 indicates adequate definition of cases; 2, cases are representative of population; 3, community controls; 4, controls have no history of colorectal neoplasia; 5A, study controls for age and gender; 5B, study controls for additional factor(s); 6, ascertainment of exposure by blinded interview or record; 7, same method of ascertainment used for cases and controls; and 8, nonresponse rate the same for cases and controls. For cohort studies, 1 indicates exposed cohort truly representative; 2, nonexposed cohort drawn from the same community; 3, ascertainment of exposure; 4, outcome of interest not present at start; 5A, cohorts comparable on basis of age and gender; 5B, cohorts comparable on other factor(s); 6, quality of outcome assessment; 7, follow-up long enough for outcomes to occur (at least 1 year); and 8, complete accounting for cohorts (>75% follow-up or description provided of those lost).