Chicago Heart Association Detection Project in Industry: Employees of 85 firms in the greater Chicago area were screened between the Fall of 1967 to early 1973. The total labor force among these companies was over 75,000 persons. The volunteer rate for the screening was 55 percent. All employees were encouraged to participate irrespective of job type or shift worked. At each employment site data were collected on smoking habits, previous medical diagnosis, current treatments for hypertension, heart disease and diabetes, height and weight, age, sex, race, heart rate.