Usual Dietary Intakes: SAS Macros for Running the NCI Method
NCI has developed two macros for estimating usual intakes. One -- MIXTRAN -- fits
the model to obtain parameter estimates and allows for the evaluation of covariate
effects. The other -- DISTRIB -- uses parameter estimates from MIXTRAN and a Monte
Carlo method to estimate distributions of usual intake. These macros can be used jointly
to estimate the distribution of usual intakes of both foods and nutrients. The MIXTRAN
macro alone is sufficient for testing covariate effects on either food or nutrient
intakes. The DISTRIB Macro is not intended to be used alone.
Documentation for both macros is provided in the
NCI Users' Guide for Analysis of Usual Intake Distributions (PDF).
To help analysts get started, NCI has developed several sample programs. These
programs employ the MIXTRAN and DISTRIB macros in conjunction with a preliminary analytic
dataset containing data from the National Health and Nutrition Examination Survey
(NHANES). The preliminary dataset is based on NHANES 2001-04 data, but includes the
addition of balanced repeated replication (BRR) weights, imputed values for some of the
MyPyramid equivalents data, and differences in a few variable names.