Longitudinal Analysis of the Dynamics and Risk of Coronary Heart Disease in the Framingham Study

Abstract
Statistical methods designed specifically for the analysis of chronic disease incidence and progression in longitudinal studies are presented. These methods model the risk of acute phases of chronic disease separately from the temporal change in risk variables. This could be accomplished because, under a specific biological model of the disease mechanism, the problems of estimating the risk of an acute event and of predicting the change in risk variables are independent. A quadratic equation relating risk variable values to chronic disease risk and a system of linear equations predicting future risk variable values from present values may be estimated separately. Taken together, they utilize the full information available in a longitudinal study on the temporal dimension of chronic disease progression. The model possesses a number of attractive statistical and theoretical properties. These methods are applied to longitudinal data from the Framingham study on coronary heart disease (CHD) in males. A quadratic function relating the risk of a CHD event to selected risk variables (age and the natural log of serum cholesterol, uric acid, diastolic blood pressure and pulse pressure) is estimated from measurements made at 4 points equally spaced in time (2 yr) with a further morbidity follow-up at a 5th point. The risk function predict CHD risk accurately. Apart from the linear effects of the risk variables, cohort effects, quadratic effects and interaction effects are important predictors of CHD risk. The linear regression equations used to predict future risk variable values show that there is an intricate network of cross-temporal associated with higher levels of risk, and indirectly, by causing other risk variable values to change with time. Several different roles that risk variables might play in CHD incidence are identified.

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