Estimating the combined effect of several disease precursors in health risk appraisal.

Health risk appraisal is an attractive health education technique but suffers from methodologic weaknesses. Many of the problems center on the formula that is usually used to estimate the combined effects of different disease precursors. The formula does not reflect current models of disease causation, underestimates the effects of protective factors, and confounds the effects of different precursors. We suggest a modification that resolves these problems by estimating the prevalence and associated composite relative risk for each combination of precursors before calculating the numerical estimate of combined risk. This method can be applied to the many diseases for which the data needed to support a multivariate approach are not available. We recommend its incorporation into existing appraisal instruments.