NIS Survey Methods
The National Immunization Survey (NIS) uses random-digit dialing to
survey households with age-eligible children, followed by a mail survey
to the eligible children’s vaccination providers to validate the
vaccination information. The household telephone survey asks questions
about childhood immunization for children aged 19–35 months of age and
requests parental permission for contacting children’s vaccination
providers. The mail survey of vaccination providers asks the types of
immunizations, dates of administration, and additional data about
facility characteristics. The Council of American Survey and Research
Organizations response rates for NIS years 2001–2006 were consistently
above 64% (range 64.5%–76.1%). A more detailed description of the
methods can be found at
http://www.cdc.gov/nis.
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.
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 ‘or 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
“How old was [child’s name] when [child’s 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 (“How 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 show the trends of exclusive breastfeeding by year of
birth separately for children whose caregivers were interviewed before and
after January 2006.
Table A1. Changes in breastfeeding questions, National Immunization Survey 2001-2006
| Questions 2001–2003 | Questions 2004–2005 | 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’s name] when [child’s 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’s 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’s milk, water, sugar water, solid foods or anything else. | 3. How old was [child’s 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’s milk, sugar water, baby food, or anything else that [child] may have been given, even water. How old was [child’s name] when (he/she) was first fed anything other than breast milk or formula? |
Selecting the NIS Survey Population
The NIS covers all 50 states, the District of Columbia, and selected geographic areas within states. Using a computer generated list across the country, the NIS identifies households with children aged 19–35 months old and interviews the person who is most knowledgeable about the child’s immunization status. Each year, approximately 35,600 completed phone interviews are obtained nationally in the NIS.
Analysis of Breastfeeding Practice Data by Year of Child Birth
Following the 2006 survey, we combined survey years 2001 through 2006 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). All analyses were 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 |
|---|---|---|---|---|---|---|---|
| 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 |
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)
Please note: Some of these publications are available for download only as *.pdf files. These files require Adobe Acrobat Reader in order to be viewed. Please review the information on downloading and using Acrobat Reader software.
* Links to non-Federal organizations found at this site are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization Web pages found at these links.
Page last updated: July 27, 2007
Content Source: Division of Nutrition, Physical Activity and Obesity, National Center for Chronic Disease Prevention and Health Promotion