10 National Health and Nutrition Examination Survey
10 National Health and Nutrition Examination Survey
10.1 Introduction
Chapter 10 covers the National Health and Nutrition Examination Survey (NHANES). The NHANES has been collected by the National Center for Health Statistics (NCHS) since 1960 to monitor and explore trends in the health status and nutritional status among all individuals in the United States (US).1 It became formally known as the NHANES in 1999. A unique aspect of the NHANES in comparison to other surveys is that the NHANES collects data from both subjective interviews and objective physical examinations and laboratory tests. Objective measures are collected at mobile examination centers.1 This chapter includes details on: how data are collected; how data are made publicly available as machine-actionable data files; what variables must be included to address design features of the complex sample; the strengths and limitations of the survey; and practical tips for conducting statistical analysis; and how to answer research questions using a case study. The practical tips provided for analysis of NHANES data are based on the author’s previous experiences analyzing NHANES data to answer questions related to associations between predisposing and enabling factors that contribute to health behaviors, morbidity, mortality and health services use. The NHANES case study will explore racial and ethnic differences in 24-hour movement guideline adherence, specifically sedentary behavior guideline adherence. This objective is part of a series of research questions designed to evaluate how physical activity, sleep, and sedentary behavior are associated with cognitive health outcomes among adults in the US. The bulk of the chapter will comprise of section 10.6: NHANES Case Study in order to give the readers hands-on practice downloading and cleaning large databases and conducting basic categorical data analysis using PROC SURVEYFREQ and PROC SURVEYLOGISTIC. The syntax provided was created for use with SAS 9.4 .
10.2 Data Collection
The NHANES uses a cross-sectional study design to collect data from personal interviews, physical examinations and laboratory data among noninstitutionalized adults and children. Data are compiled and released in 2-year cycles as public-use data files.2 From 2011-2014, the complex sample design included 13 major strata, 4 minor strata and 8 primary sampling units (PSU).2 The study design oversampled Hispanics, non-Hispanic Blacks and non-Hispanic Asians, persons below 130% of federal poverty level and persons ages 80 years and older. Data were collected from five US regions, with California separated as a distinct group. Starting in 2015, the design changed to 14 major strata, 4 minor strata and 4 PSUs.3 Individuals were oversampled below 185% federal poverty level instead of 130% and California was not separated from all other states in the new design.
10.3 Data Files
The most recent NHANES iterations (2017-2020) included demographic, dietary, medical examination, l