Deaths in the cohort were usually reported by next-of-kin or postal authorities. At the completion of each mailing cycle, the National Death Index was searched for names of non-respondents who might have died. By comparing deaths ascertained from independent sources, the study ascertained on estimated 98.25 percent of deaths. Death certificates were obtained from state vital statistics departments to confirm all reported deaths. For all death certificates indicating possible cardiovascular disease, permission to obtain further information was requested from family members. Confirmed coronary heart disease death required additional information beyond the death certificate such as autopsy reports, ECG and enzyme changes of myocardial infarction prior to death, classical chest pain immediately prior to death, prior documented myocardial infarction or angina, or prior cardiac catheterization showing severe coronary disease.