The potential for a preventive approach in cardiovascular diseases was based on the large differences in disease rates found between populations and the strong associations between individual risk factor levels and disease rates within high risk cultures. The congruence of these population observations with clinical evidence and with plausible mechanisms of cause, strengthened inference of their causal importance. Further, the safety and feasibility were well established of modifying individuals' cardiovascular risk characteristics and changing personal health behavior through medical and educational strategies. Finally, the dynamic nature of the changes in vital statistics on deaths reported from hypertension, stroke, and coronary heart disease (CHD) in many nations, at the rate of one to two percent a year and greater, both upward and downward, indicated their preventability, though none of these trends was adequately explained when the study began in 1980.