Assessing Changes in Within Individual Variation Over Time for Nutritional Intake Data Using 24 Hour Recalls from the National Health and Examination Survey

Nutritional surveys often use 24 hour recalls to assess the nutritional intake of certain populations. The National Health and Examination Survey (NHANES) collects two 24-hour recalls for each individual in the study. This small sampling can lead to a great deal of variation due to day-to-day differences in an individual?s intake, making it difficult to assess ?usual intake.? The ISU method is implemented in the PC-Side software package, breaking our observed variation into two components: within individual variation (WIV) and between-individual variation (BIV). In this paper, we will use the PC-Side software to get WIV estimates for several different age, gender, and nutrients from NHANES nutrition data. We will look at how WIV estimates change over time and using past WIV estimates to get a ?usual intake? distribution and the calculated proportion below an estimated average requirement (EAR)