Components of variance in dietary data for an elderly population

The day-to-day variance (intraindividual) in dietary intake is estimated for a variety of dietary constituents in a population of healthy free-living elderly. Daily food records were collected on three consecutive days for each of two years for 50 individuals. Year-to-year variance in dietary intake is also examined. The role of intraindividual variability as a source of error in the measurement of usual or habitual dietary intakes is emphasized. The results confirm previous findings that intraindividual variance is generally as large as or larger than interindividual variance. Ratios of intra- to interindividual variance ranged from 0.83 for energy intake in females to over 5.0 for cholesterol intake among males. Significant year-to-year variance was seen for some nutrients. It is also shown that inclusion of supplemental intakes for vitamins and minerals can significantly reduce the ratio of intra- to interindividual variance for these nutrients.