# Estimating Population-Level Distributions of Usual Dietary Intake

### Purpose

The term “dietary intake” in this module includes foods and beverages reported on the 24-hour recalls. Researchers often are interested in estimating the distribution of usual intake of dietary components for a population or subpopulation. This module focuses on using the method developed by researchers at NCI and elsewhere (i.e., the “NCI method”) for this purpose, comparing and contrasting to other methods, as appropriate. It also directs interested users to references on the Iowa State University (ISU) and National Research Council (NRC) methods. Due to the different statistical properties of distributions for ubiquitiously-consumed dietary constituents (e.g., nutrients and food groups consumed on a daily or almost daily basis), and episodically-consumed dietary constituents (e.g., nutrients and food groups that are not consumed every day for more than about 5% of the population), different models are fit for ubiquitously-consumed and episodically-consumed dietary constituents. In the NCI method, the model for ubiquitously-consumed dietary constituents is a simple case of the model for episodically-consumed foods.

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.

### Task 1: Estimating Distributions of Usual Intake for a Single Ubiquitously-consumed Dietary Constituent for One Population or Subpopulation

This task describes the use of statistical methods to estimate the distribution of usual intake for one ubiquitously-consumed dietary constituent, such as a nutrient that is consumed daily, for a population or for one subpopulation. It also describes the steps analysts should take to calculate this estimation using the NCI method specifically.

- Key Concepts about Estimating Distributions of Usual Intake for a Single Ubiquitously-consumed Dietary Constituent
- How to Estimate the Distribution of Usual Intake for a Single Ubiquitously-consumed Dietary Constituent for One Population or Subpopulation using the NCI Method
- Download Sample Code and Datasets

### Task 2: Estimating Distributions of Usual Intake for a Single Ubiquitously-consumed Dietary Constituent for Two or more Subpopulations using a Covariate

This task describes the use of statistical methods, for subpopulations defined by a covariate, to estimate the distribution of usual intake for one ubiquitously-consumed dietary constituent, such as a nutrient that is consumed daily, using a covariate to define the subpopulation. It also describes the steps analysts should take to calculate this estimation using the NCI method.

- Key Concepts about Estimating Distributions of Usual Intake for a Single Ubiquitously-consumed Dietary Constituent with a Few Days of 24-hour Recalls for Subpopulations using a Covariate
- How to Estimate Distributions of Usual Intake for a Single Ubiquitously-consumed Dietary Constituent with a Few Days of 24-hour Recalls for Subpopulations using a Covariate
- Download Sample Code and Datasets

### Task 3: Estimating Distributions of Usual Intake for a Single Episodically-consumed Dietary Constituents

This task describes the use of a two-part model for estimating usual intake of a single episodically-consumed dietary constituent, such as a food group that is not consumed on a daily basis, and how to estimate the distribution of usual intake of a single episodically-consumed dietary component using the NCI method.

- Key Concepts about Estimating Distributions of Usual Intake for a Single Episodically-consumed Dietary Constituent
- How to Estimate Distributions of Usual Intake for a Single Episodically-consumed Dietary Constituent using the NCI Method
- Download Sample Code and Datasets

### Task 4: Estimating Population Distributions of Ratios of Usual Intakes of Two Dietary Constituents that are Ubiquitously Consumed

This task describes the use of a model for estimating the population distribution of the ratio of usual intakes of two ubiquitously-consumed dietary constituents, such as a nutrient and energy, and how to estimate this ratio using the NCI method.

- Key Concepts about Estimating Distributions of Usual Intake for the Ratio of Two Ubiquitously-consumed Dietary Constituents
- How to Estimate Distributions of Usual Intake for the Ratio of Two Ubiquitously-consumed Dietary Constituent Using the NCI Method
- Download Sample Code and Datasets

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