NIS Survey Methods
Each year, the CDC National Immunization Program, in partnership with CDC抯 National Center for Health Statistics, conducts the National Immunization Survey (NIS). The NIS uses random-digit dialing to survey households with children aged 19� months. The household telephone survey asks questions about childhood immunization. Beginning July 2001 and continuing through December 2002, a sample of respondents was asked about breastfeeding using the original questions listed in Table A1. Starting January 2003, all respondents to the household telephone survey were asked these breastfeeding questions. The Council of American Survey and Research Organizations response rates for NIS years 2001�07 were consistently above 64% (range 64.5%�.1%). A more detailed description of the methods can be found at http://www.cdc.gov/nis.
Wording of the Breastfeeding Questions
The breastfeeding questions used in the NIS were modified in 2004 and
2006 (Table A1). In January 2004, the third question was modified slightly
to remove 憃r water� from the first part of the question and add it to the
list of items other than breast milk. Additionally, the interviewers were
instructed to always read the clarification of foods and liquids to
consider. Our examination of the influence of this question change on the
rate of exclusive breastfeeding at 3 and 6 months of age revealed a minimal
effect.
In 2006, additional changes were made to two of the NIS breastfeeding
questions (Table A1). These changes were based on the results of cognitive
testing of the questions used prior to 2006. Question 2 was revised to read
揌ow old was [child抯 name] when [child抯 name] completely stopped
breastfeeding or being fed breast milk?� The wording change on question 2
resulted in a minimal effect on our reported duration of breastfeeding.
Question 3 (揌ow old was [child] when s/he was first fed something other
than breast milk?�) was asked as two separate questions in 2006, which
yielded significantly lower estimates of exclusive breastfeeding. Because of
this large effect, we only show trends of exclusive breastfeeding and
formula supplementation of breast milk for children whose caregivers were
interviewed after December 31 2005.
The 2006 breastfeeding questions continue to be used in the NIS survey.
Table A1. Changes in breastfeeding questions, National Immunization Survey 2001-2006
| Questions 2001�03 | Questions 2004�05 | Revised Questions in 2006 |
|---|---|---|
| 1. Was [child] ever breastfed or fed breast milk? | 1. Was [child] ever breastfed or fed breast milk? | 1. Was [child] ever breastfed or fed breast milk? |
| 2. How long was [child] breastfed or fed breast milk? | 2. How long was [child] breastfed or fed breast milk? | 2. How old was [child抯 name] when [child抯 name] completely stopped breastfeeding or being fed breast milk? |
| 3. How old was [child] when s/he was first fed something other than breast milk or water? [If respondent hesitates, add: This includes formula, juice, cow抯 milk, sugar water, solid foods or anything else.] | 3. How old was [child] when s/he was first fed something other than breast milk?* This includes formula, juice, cow抯 milk, water, sugar water, solid foods or anything else. | 3. How old was [child抯 name] when (he/she) was first fed formula? |
| 4. This next question is about the first thing that [child] was given other than breast milk or formula. Please include juice, cow抯 milk, sugar water, baby food, or anything else that [child] may have been given, even water. How old was [child抯 name] when (he/she) was first fed anything other than breast milk or formula? |
Analysis of Breastfeeding Practice Data by Year of Child Birth
We combined all available survey years to calculate breastfeeding indicators by year of child birth (Smith et al 2006). Because children are 19—35 months of age at the time of the parent interview, each survey year represents children born over three years (Table A2). Breastfeeding rates among children in a birth year are released when approximately 2/3rds of the children born in that year have been surveyed. The rates are labeled provisional until they are replaced the following year with final rates based on all children in the birth year. All analyses are conducted using statistical software that accounts for complex sample design.
Table A2
| NIS survey year | Birth months represented | Birth year 1999 | Birth year 2000 | Birth year 2001 | Birth year 2002 | Birth year 2003 | Birth year 2004 | Birth year 2005 |
|---|---|---|---|---|---|---|---|---|
| 2001 | 8/98-5/00 | X | X | |||||
| 2002 | 2/99-5/01 | X | X | X | ||||
| 2003 | 2/00-5/02 | X | X | X | ||||
| 2004 | 2/01-5/03 | X | X | X | ||||
| 2005 | 2/02-5/04 | X | X | X | ||||
| 2006 | 2/03-5/05 | X | X | X | ||||
| 2007 | 2/04-5/06 | X | X |
References
Smith PJ, Zhao Z, Wolter KM, Singleton JA, Nuorti JP. Age-period-cohort
analyses of public health data collected from independent serial
cross-sectional complex probability sample surveys. Seattle, WA: Joint
Statistical Meeting; 2006. Available at
http://www.amstat.org/Sections/Srms/Proceedings/y2006/Files/JSM2006-000537.pdf*
(PDF - 125k)
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Page last updated: July 27, 2007
Content Source: Division of Nutrition, Physical Activity and Obesity, National Center for Chronic Disease Prevention and Health Promotion