Estimation of the Usual Intake Distributions of Ratios of Dietary Components

In recent years, it has become apparent that ratios of usual intakes of dietary components, such as the percent of calories from fat or the percent of calories from standard fat, are important indicators of dietary adequacy. The problem of estimating a percentile of the distribution of ratios of usual intakes of nutrients presents problems that arise from the fact that, from a statistical point of view, ratios of dietary components can be viewed as ratios of random variables. The methods developed by Nusser et al. (1995) to estimate usual intake distributions of nutrient, for example, cannot be directly applied to ratios, since the ratio of usual intakes is not equal to the mean of the ratio of daily intakes. In this paper we discuss the problem of estimating the intake distribution of ratios of dietary components by using an extension of the method developed by Beale (1962). The method we propose consists of first estimating the daily ratio of dietary components for each individual to obtain a nearly unbiased ratios estimate, and then applying the method developed at Iowa State University to estimate the distribution of usual intakes of the ratio. We use data collected in the 1989-91 CSFII, and consider six ratios to illustrate the procedure