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NHANES Dietary Web Tutorial

Introduction

What are the NHANES dietary data?

The National Health and Nutrition Examination Surveys (NHANES) dietary data provide a snapshot of the food intakes and nutritional status of the U.S. population.

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The National Health and Nutrition Examination Surveys (NHANES) is the only national survey that collects extensive health and nutrition information from face-to-face interviews and medical examinations.  For many decades, the National Center for Health Statistics (NCHS) and the U.S. Department of Agriculture (USDA) have collected dietary data -- NCHS always collected dietary data as part of NHANES, whereas the USDA used its own surveys.  USDA’s national food consumption surveys were initially designed to help people achieve economical and nutritious diets.  Over time, these surveys broadened in scope and purpose to measure knowledge and attitudes about diet and health as well as to assess food and nutrient intakes. 

In 2002, USDA and NCHS integrated their dietary data collection efforts and the dietary recall data are now collected in a joint survey effort called What We Eat in America (WWEIA).   These data as well as other NHANES data about dietary supplement use, diet behaviors, and food frequency information are a valuable resource that respond to a variety of public health and research priorities.  In 2003-2006, the National Cancer Institute (NCI) supported the inclusion of a Food Frequency Questionnaire in the NHANES to aid in the examination of usual food intakes and their relationship to health outcomes.

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Why was this tutorial created?

The NCI, NCHS, and USDA developed this web-based tutorial to meet the growing demands of NHANES dietary data users and to promote broader and more proficient use of NHANES dietary data.

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Whether novice or experienced, all users face similar challenges when using NHANES dietary data due to the complexity of the survey design and data structure.  This tutorial was designed so that all users learn to:

  • efficiently locate pertinent information on the NCHS website, which is constantly updated and evolving;

  • quickly retrieve NHANES dietary data files and supplementary information, a frequent challenge given the complex structure and large amount of data available;

  • correctly prepare an analytic dataset and create appropriate food and nutrient variables; and

  • correctly conduct statistical analyses that achieve the analyst’s research objectives with appropriate attention paid to the nuances of the data and its complex sample design, weighting requirements, and data structure.

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What does the tutorial provide?

This tutorial walks you through the steps of conducting an analytical project from beginning to end, with examples of many common analytic procedures. Relevant dietary data information and nuances, tips, and explanations for SAS or SUDAAN programs; downloadable sample program code; and analytical guidance are organized and integrated into different modules and tasks to facilitate this learning process. 

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The tutorial is intended to be:

  • a step-by-step course on dietary data retrieval and analysis for new users;

  • a self-learning tool for novice and infrequent users to supplement their knowledge of the wide range of dietary data available in NHANES and the analysis techniques required to properly analyze these complex datasets; and

  • a reference for experienced researchers highlighting NHANES analytic nuances and sample program code.

To best serve the needs of a wide range of users, this tutorial has included a large amount of information.  The information is organized in such a way that those who would like to review all information may do so, while others can efficiently bypass sections that are not of interest to them.  Overall, this tutorial provides a complete on-line learning tool.

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What's the best way to use the tutorial?

Your own background and learning style will dictate how you can best use this tutorial.

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  • If you are a beginning NHANES dietary data user, you may want to work through the tutorial in a linear fashion, starting with the modules that orient you to the dietary data, then continuing with the modules about how to prepare an analytic dataset and how to conduct various types of analyses.

  • If you are an experienced NHANES dietary data user and you are searching for specific information or types of assistance, you can pick and choose topics of interest among the modules or even among tasks within modules.

You are encouraged to use the tutorial's features and content to suit your own needs:

  • a linear path for users who need step-by-step self-guided training;

  • index pages and easy navigation throughout modules that allow you to limit your training to information on an “as needed” basis;

  • checklists, summary tables, and animated demonstrations with audio explanation to enhance learning;

  • real-life examples to assist you through the various processes of data preparation and data analysis; 

  • sample code and data files for you to practice skills and run analyses using your own software;

  • annotated results with interpretation to help you troubleshoot your own analyses; and

  • links to related references and outside resources.