# Evaluating the Effects of Covariates on Usual Dietary Intake

### Purpose

Researchers are often interested in variables that are associated with intake of dietary constituents. For example, they may want to know whether a personal characteristic, like age, is associated with consumption of a particular food or nutrient. This type of inference can be made from fitting the model that is used in the method developed by researchers at NCI and elsewhere (i.e., the “NCI method”). The term “dietary intake” in this module refers to food and beverages reported on the 24-hour recalls.

### Task 1: Evaluating the Effects of Covariates on Usual Intake of a Single Ubiquitously-Consumed Dietary Constituent

When a dietary component is ubiquitously consumed, as is the case for many nutrients and some food groups, a single-part model can be used to estimate the amount of the dietary component consumed because it is not necessary to estimate the probability of consumption as in a two-part model. This task describes how to fit the model with covariates and how to evaluate the effects of the covariates on usual intake consumption.

Many of the statistical methods used in this course are advanced, and may require consultation with a statistician. For modules 18-22, it is required that you have the statistical knowledge of mixed effects models, and program knowledge of calling in SAS macros. Since Module 18 provides the background information for Modules 19-22, it is advised that you carefully read Module 18 first before tackling other modules.

- Key Concepts about Evaluating the Effects of Covariates on Usual Intake of a Single Ubiquitously-Consumed Dietary Constituent
- How to Evaluate the Effects of Covariates on Usual Intake of a Single Ubiquitously-Consumed Dietary Constituent
- Download Sample Code and Datasets

### Task 2: Evaluating the Effects of Covariates on Usual Intake of a Single Episodically-Consumed Dietary Constituent

When a dietary component is episodically consumed, as is the case for many foods and food groups, a two-part model to estimate the probability of consumption and the amount of the dietary constituent consumed on the consumption day is used. This task describes how to fit this two-part model with covariates and how to evaluate the effects of the covariates on usual intake consumption.

- Key Concepts about Evaluating the Effects of Covariates on Usual Intake of a Single Episodically-Consumed Dietary Constituent
- How to Evaluate the Effects of Covariates on Usual Intake of a Single Episodically-Consumed Dietary Constituent
- Download Sample Code and Datasets

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