NIS-Child Data Analysis

At a glance

Learn more about the National Immunization Survey-Child (NIS-Child) and how CDC determines breastfeeding rates by birth years and how often CDC releases the rates.

A mom breastfeeds her baby in front of desk with a laptop on it.

Analysis: breastfeeding practice data by child's birth year

CDC combines survey years to calculate breastfeeding indicators by year of child's birth.1 Children were aged 19 to 35 months when their caregivers were interviewed. Each survey year represents children born over 3 years (see table below).

For each birth year, CDC estimates the percentage of infants who were ever breastfed or fed breast milk in the following categories:

  • "Ever breastfed."
  • "Breastfed at 6 months."
  • "Breastfed at 12 months."
  • "Exclusively breastfed through 3 months."
  • "Exclusively breastfed through 6 months."

"Ever breastfed" is estimated by the question: "Was [child] ever breastfed or fed breast milk?"

"Breastfeeding duration" is estimated by the question: "How old was [child] when he/she completely stopped breastfeeding or being fed breast milk?"

Exclusive breastfeeding is defined as ONLY breast milk (no solids, water, or other liquids). The exclusive breastfeeding duration is estimated by the two survey questions about age. These questions include the child's age when he/she was first fed formula and first fed anything other than breast milk or formula (including water).

Breastfeeding initiation, duration, and exclusivity rates are calculated among all infants surveyed.

Formula supplementation

CDC calculates the percentage of breastfed infants who are supplemented with formula (with or without other supplementary liquids or solids) before 2 days, 3 months, and 6 months old. The rates of formula supplementation are calculated among infants who are also breastfeeding at each respective age.

How often CDC releases rates

CDC releases breastfeeding rates every year. Before 2013, CDC labeled the rates based on two survey years as provisional until they were replaced the following year with final rates based on three survey years.

CDC now reports one final rate based on two survey years only. This is because adding a third year of survey data has little effect on the breastfeeding rate. The third year also results in a margin of error only about 20% smaller than with two survey years. CDC conducts all analyses using statistical software that accounts for complex sample design.

NIS data used to calculate breastfeeding rates in each birth cohort

Years of breastfeeding data from National Immunization Survey used to calculate breastfeeding rates for each birth cohort1
NIS-Child survey year Birth month/year represented Birth year 2014 Birth year 2015 Birth year 2016 Birth year 2017 Birth year 2018 Birth year 2019 Birth year 2020 Birth year 2021
2015 1/12–5/14 X
2016 1/13-5/15 X X
2017 1/14-5/16 X X
2018 1/15-5/17 X X
2019 1/16-5/18 X X
2020 1/17-5/19 X X
2021 1/18-5/20 X X
2022 1/19-5/21 X X
2023 1/20-5/22 X
1Starting with the 2010 births, CDC includes only the FIRST 2 survey years of data containing the cohort for annual estimates of breastfeeding rates by each birth cohort.
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Content Source:
National Center for Chronic Disease Prevention and Health Promotion (NCCDPHP)
  1. Hill HA, Singleton JA, Yankey D, Elam-Evans LD, Pingali SC, Kang Y. Vaccination Coverage by Age 24 Months Among Children Born in 2015 and 2016 — National Immunization Survey-Child, United States, 2016–2018. MMWR Morb Mortal Wkly Rep 2019;68:913–918. DOI: 10.15585/mmwr.mm6841e2.