Location: Food Surveys
Title: Within-Individual Variance Estimates for Nutrients from What We Eat in America, Nhanes 2002 Author
Submitted to: World Wide Web
Publication Type: Other
Publication Acceptance Date: August 23, 2005
Publication Date: September 15, 2005
Citation: U.S. Department of Agriculture, Agricultural Research Service. 2005. Within-individual variance estimates for nutrients from What We Eat In America, NHANES 2002. Available: http://www.ars.usda.gov/ba/bhnrc/fsrg. Interpretive Summary: This release of estimates of within-individual variance components enables analysts to estimate usual, or long-term, daily nutrient intake from datasets comprised of the nutrient intake, over a single 24-hour period, for each person in a sample of a gender/age group. Usual intake estimates are required for statistical comparisons with the Dietary Reference Intakes (DRIs) to assess the adequacy of nutrient intake within population subgroups. In order to estimate usual nutrient intake distributions using one of the methods suggested by the Institute of Medicine of the National Academies, it is necessary to have either a set of intake data from a group of individuals for which multiple days of intake are available or a set of nutrient intakes from individuals providing only one daily intake each and an estimate of within-individual variability from an external source. What We Eat in America (WWEIA), NHANES 2001-2002, the dietary component of the National Health and Nutrition Examination Survey, collected two days of intake data from individuals during the year 2002 but the 2001-2002 public data release contains only the first day of intake for all individuals for confidentiality reasons. These estimates of within-individual variance components were derived in part through the analysis of the second day of intake which is not directly available to the public. They were used along with the public release of WWEIA 2001-2002 to prepare the report: "What We Eat in America, NHANES 2001-2002: Usual Nutrient Intakes from Food Compared to Dietary Reference Intakes." Analysts wishing to perform similar analyses, either with WWEIA or with other nutrient intake datasets comprised of only one intake per individual, may do so through the use of these variance estimates.
Technical Abstract: These estimates of within-individual variance components were produced to permit the estimation of distributions of the usual intake of nutrients and other dietary components from intake datasets that contain only one day of nutrient intake per person. They were used in preparing the report "What We Eat in America, NHANES 2001-2002: Usual Nutrient Intakes from Food Compared to Dietary Reference Intakes." They may have additional applications in analysis of What We Eat in America (WWEIA), NHANES 2001-2002 data or of other intake datasets comprised of only one day of intake per individual. The variance estimates are provided for 35 nutrients and dietary components for 21 gender/age groups including 14 gender/age groups for which the Institute of Medicine of the National Academies established Dietary Reference Intakes and 7 summary groups. The within-individual variance component estimates are provided in two formats: a comma-delimited text file and a SAS(R) system file of the XPORT type. Both files have one record for each nutrient and gender/age group combination containing the following five fields: gender/age group represented numerically, a text description of the gender/age group, the nutrient represented numerically, a text description of the nutrient, and the within-individual variance component estimate.