How You Were Selected

Key points

  • The National Health and Nutrition Examination Survey uses a scientific process and U.S. Census information to select participants.
  • The four-stage process chooses several areas we visit each year.
  • In the last stage, scientific methods identify people like you who we ask to complete our interviews, health exam, and laboratory tests.
Illustration of diverse group of people

No one can take your place!

When an NHANES representative comes to your door, you may wonder how you were chosen.

You live in one of the areas that NHANES will visit this year. Your area was randomly selected using a scientific process and U.S. Census information.

NHANES staff won't be able to visit every house in the United States or even every house in selected areas. Instead, we randomly choose which households we visit. Your house­hold is one of a few selected in your commu­nity. We need you to help accurately represent thousands of people across the country just like you.

Our selection process

A U.S. map, a neighborhood map, a house, and a computer picking people; describes selection steps outlined on the page
NHANES uses a four-stage, scientific process to select participants.

Stage 1: The NHANES selection process divides the United States into large regions. Each region is based on how similar its characteristics are to characteristics of the other regions. The process then selects smaller areas from each region. Those smaller areas are the ones NHANES will visit that year.

Stage 2: Within each of those smaller areas we will visit, our process selects neighborhoods that have a lot of households.

Stage 3: Our process then identifies all houses, condos, apartments, and other households within the neighborhoods chosen in Step 2. A few households from each of these neighborhoods then proceed to Step 4.

Stage 4: NHANES will contact each selected household to ask a short set of questions about everyone in the household. The questions cover things like each person's age, race, and gender. Our computer program then randomly selects at least one member from each eligible household to participate in NHANES.