In 1985 when the study was initiated, there were surprisingly little data on the distribution of risk factors among subgroups of the population and the changes occurring over time. These issues assumed greater importance as the decline in coronary heart disease mortality focused interest on the role of primary prevention through alteration of risk factors. In review of the potential contributions to this decline, it was noted that cessation of cigarette smoking, better blood pressure control and decrease in total serum cholesterol may have accounted partially for the decline in coronary heart disease mortality. However, these observations overlooked the possibility that observations in the total population or confined to specific socioeconomic groups may fail to disclose differential changes in particular population segments. For example, Americans in the higher educational and income groups experienced rapid and marked changes in risk behaviors while less educated, lower income Americans or specific racial/ethnic groups experienced no beneficial changes. The majority of cohort studies followed rather select groups and most cross-sectional surveys also had little sociodemographic variability. However, focusing public health, educational and medical intervention efforts required that particular groups at greater risk or experiencing less beneficial secular change be identified and targeted for greater efforts.