# Overview of NHANES Survey Design and Weights

### Purpose

NHANES uses a complex sampling design and constructs sample weights to produce nationally representative data. Learning about the features of the NHANES survey design and weighting will help ensure that the results of your analyses represent unbiased estimates with accurate statistical significance levels.

### Task 1: Explain NHANES Survey Design

NHANES data are obtained through a complex, multistage, probability sampling design that selects participants who are representative of the civilian, non-institutionalized U.S. population. Participants are not selected by a simple random sample. Over-sampling of certain population subgroups is done to increase the reliability and precision of health status indicator estimates for those groups. Failing to account for the sampling design in your analyses may result in biased estimates and overstated significance levels.

### Task 2: Explain NHANES Sample Weights

NHANES has constructed various sample weights
for single 2-year survey cycles to take into account survey
non-response, over-sampling, post-stratification, and sampling
error. This task describes how sample weights are constructed in
NHANES. Due to the way NHANES participants are selected, **sample
weights always must be used** to produce an unbiased national
estimate.

For additional information on these topics, please see the Continuous NHANES Web Tutorial Weighting module.

##### Contact Us:

- National Center for Health Statistics

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Hyattsville, MD 20782 - 1 (800) 232-4636
- cdcinfo@cdc.gov