Usual Dietary Intakes: SAS Macros for Analysis of a Single Dietary Component

Three macros are available to support modeling of a single dietary component (either consumed nearly every day or episodically):

• MIXTRAN Macro: fits a model to obtain parameter estimates and allows for the evaluation of covariate effects.
• DISTRIB Macro: uses parameter estimates from MIXTRAN and a Monte Carlo method to estimate the distribution of usual intake for a food or nutrient.
• INDIVINT Macro*: uses parameter estimates from MIXTRAN or other appropriate model to predict individual food or nutrient intake for use in a disease model.

* Note that the INDIVINT macro requires SAS IML. The SAS Institute has reported an error that can occur when running SAS IML in SAS 9.2 TS1MO - the error relates to variables with missing values. Read the SAS Problem Note and get a link to the Hot Fix. The problem is fixed in SAS 9.2 TS2M2, and this error is not encountered in SAS 9.1.3.

The MIXTRAN macro alone is sufficient for testing covariate effects on intakes of a dietary component. The DISTRIB and INDIVINT macros are generally used in conjunction with the MIXTRAN macro.

Documentation for all three macros is provided in the User's Guide for Analysis of Usual Intakes: For use with versions 1.1 of the Mixtran, Distrib and Indivint SAS macros (PDF). Applications of these macros are described in Tooze et al, 2006 and Kipnis et al, 2009. 

To help analysts get started, NCI has developed sample programs and analytic datasets. These programs employ the various macros in conjunction with preliminary analytic datasets containing data from the National Health and Nutrition Examination Survey (NHANES). The first three examples use a dataset that is based on NHANES 2001-04 data; it includes the addition of balanced repeated replication (BRR) weights, imputed values for some of the MyPyramid equivalents data, and some variable names that differ from the names used in the original NHANES file. The last example uses a dataset based on NHANES 2003-04 data, with a small set of variables used to illustrate the method.

• Sample programs and output:
  • Example 1 (ZIP) illustrates model fitting and estimation of the distribution of usual intake for a dietary component that is consumed nearly daily.
  • Example 2 (ZIP) illustrates model fitting and estimation of the distribution of usual intake for a dietary component that is consumed episodically.
  • Example 3 (ZIP) illustrates time-saving programming techniques and macro features for a more complicated situation.
  • Example 4 (ZIP) illustrates model fitting to evaluate the relationship between a single dietary component and a health parameter.
• Analytic datasets for examples
• Details of dataset contents for examples 1-3 (PDF)
• Details of dataset contents for example 4 (PDF)