In 1960, the WCGS recruited 3,154 employed men, ages 39 to 59, who were initially free of coronary heart disease and followed them for 8.5 years for coronary heart disease incidence. In 1972 MRFIT began recruiting 12,866 men, ages 35 to 57, selected for elevation of one or more risk factors, but free from coronary heart disease and followed them for an average of seven years after randomization to a risk factor modification group or to a control group referred to their own physicians for treatment. Both studies used the Structured Interview to assess Type A behavior.