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Category: Project

Description: To determine the prevalence of inadequate or excessive nutrient intakes in a population, repeated 24-hour dietary intake measurements per subject allow for adjustment of modeled usual nutrient intake distributions for the proportion of total variance attributable to within-individual variation (WIV:total). When only single-day dietary data are available, an external adjustment factor can be used, but there is no formal guidance for selecting this value. We compiled estimates of WIV:total to describe variation in estimates across populations and settings and consider the effect of this variation on estimates of the prevalence of inadequate or excess intake. Reported ratios of within- to between-individual variance components of nutrient intake (and WIV:total) were compiled from the literature, and new values were calculated from analyses of existing data sets using a linear mixed model, adjusting for weekend (where available) and interview sequence. Nutrients assessed included total energy intake, total vitamin A, retinol, carotenoids/beta-carotene, folate, vitamin B12, thiamin, vitamin C, iron, and zinc.