published elsewhere (21–23). Briefly, eligible case subjects were men
and women who were diagnosed as survivors of a first acute MI by 2
independent cardiologists at any of the 6 recruiting hospitals in the
catchment area. To achieve 100% ascertainment, fieldworkers visited
the 6 hospitals daily. All cases met the WHO criteria for MI, which
require typical symptoms plus either elevations in cardiac enzyme
levels or diagnostic changes in the electrocardiogram (24). Cases
were ineligible if they 1) died during hospitalization, 2) were 75 y
old on the day of their first MI, and 3) were physically or mentally
unable to answer the questionnaire. Enrollment took place while
cases were in the hospital’s step-down-unit. Cases were matched by
age (5 y), sex, and area of residence to population controls who
were randomly identified with the aid of data from the National
Census and Statistics Bureau of Costa Rica. Because of the comprehensive
social services provided in Costa Rica, all persons living in
the catchment area had access to medical care without regard to
income. Therefore, control subjects came from the source population
that gave rise to the cases and were not likely to have been having
undiagnosed cardiovascular disease because of poor access to medical
care. Control subjects were ineligible if they had ever had an MI or
if they were physically or mentally unable to answer the questionnaires.
Participation was 98% for cases and 88% for controls. All
subjects gave informed consent on documents approved by the Human
Subjects Committee of the Harvard School of Public Health and
the University of Costa Rica.