2013 Child Asthma Data: Technical Information

Behavioral Risk Factor Surveillance System (BRFSS) - 2013

BRFSS Survey

In 2013, the BRFSS survey was conducted in all 50 states, the District of Columbia and in three US territories (Guam, Puerto Rico and the Virgin Islands). In each area where interviews were conducted, respondents were randomly selected from non-institutionalized civilian adults (18 years of age or older) living in households with a telephone BRFSS Data User Guide, 2013 [PDF - 204 KB]).

Child asthma prevalence data are produced from the responses to questions on BRFSS Random Child Selection and Childhood Asthma optional modules. A randomly selected adult provided responses to the child asthma questions. If the adult reported that one or more children aged 17 years or younger lived in the household, then one of the children was randomly selected as the "Xth" child. Questions on the BRFSS Random Child Selection and Childhood Asthma optional modules were asked of the "Xth" child.

Thirty-three areas and one territory used both the BRFSS Random Child Selection and Childhood Asthma optional modules in 2013. These areas were

Arizona, California, Connecticut, District of Columbia, Georgia, Hawaii, Indiana, Kansas, Louisiana, Maine, Maryland, Michigan, Mississippi, Missouri, Montana, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, Tennessee, Texas, Utah, Vermont, Washington, West Virginia, Wisconsin, Puerto Rico.

The following two asthma questions pertinent to prevalence estimation were asked on the BRFSS Childhood Asthma Prevalence optional module.

Lifetime asthma: Question number 21.1

Has a doctor, nurse or other health professional ever said that the child has asthma? (Variable name: CASTHDX2 [Yes = 1 / No = 2])

Current asthma: Question number 21.2

Does the child still have asthma? (Variable name: CASTHNO2 [Yes = 1 / No = 2])

Subgroup tables are based on data from the following questions of Random Child Selection optional module.

Question number 20.1 What is the birth month and year of the "Xth" child? (Variable name: RCSBIRTH* [Grouped into age categories years:0 - 4, 5 - 9, 10 - 14, 15 - 17])

Question number 20.2 Is the child a boy or a girl? (Variable name: RCSGENDER [Boy = 1 / Girl = 2])

Question number X1.01 Child Hispanic, Latino/a, or Spanish origin calculated variable (Variable name: _CHISPNC [Yes = 1 / No = 2])

Question number X1.02 Child Non-Hispanic Race including Multiracial (Variable name: _CRACE1 [Grouped into race categories: White, Black, Other/Multiracial races])

*The child's age was calculated by (IDATE-RCSBIRTH)/365.25, where IDATE is the interview date and RCSBIRTH is the child's birth month and year with 15th as the day.

BRFSS Sampling and Weighting Changes

The 2011 BRFSS data collection changed from a landline only sample to a dual-frame survey, landline and cellphone. The 2013 BRFSS data continues to reflect the changes initially made in 2011 in weighting methodology (raking) and the addition of cell phone only respondents. The aggregate BRFSS combined landline and cell phone dataset is built from the landline and cell phone data submitted for 2013 and includes data for 50 states, the District of Columbia, Guam, and Puerto Rico. More information about the changes to the 2011 BRFSS can be found at the CDC Surveillance Resource Center.

For data analysis, the 2011 BRFSS data should be considered a baseline year and are not directly comparable to previous years of data because of the changes in weighting methodology and the addition of the cell phone only respondents. Please see the BRFSS Frequently Asked Questions document for additional information.

Survey Design and Sample Weights

The survey design and the child-weighting methods are described in the technical document, "OVERVIEW: BRFSS 2013". [PDF - 82 KB].

Data Analysis

Data Used:

The BRFSS 2013 survey dataset was used to calculate prevalence estimates for all states that had the Random Child Selection & Childhood Asthma optional modules included in the common questionnaire.


The BRFSS 2013 survey data file was used to analyze childhood lifetime and current asthma prevalence by selected sociodemographic groups. Prevalence and standard error estimates were calculated using SUDAAN Release 11.1 (Research Triangle Institute, P.O. Box 12194, Research Triangle Park, NC 27708).

Data Management:

Responses of "don't know/not sure," and "refused" were re-coded as missing values. Children older than 18 years were excluded from further analysis.

Confidence Intervals:

The 95% Confidence Intervals(CI) were calculated using the following formula:

  • Lower 95% Confidence Interval = % prevalence – tv(sep)
  • Upper 95% Confidence Interval = % prevalence + tv(sep)

Where sep is the standard error of the prevalence percent and tv represents the student's t distribution with v degrees of freedom.

Subgroup tables are based on data analyzed by the following variables:

  • Gender: Male and Female
  • Age Group: 18-24, 25-34, 35-44, 45-54, 55-64, and 65+
  • Race: White, Black, and Other
  • Race/Ethnicity:White NH(non-Hispanic), Black NH, Other NH, and Hispanic

Small Sample Size Assumptions

When sample sizes for a particular state or territory were smaller than 50, the calculated standard error of the prevalence estimate might have been large relative to the point estimate of the prevalence value, which caused a wide 95% confidence interval. This sometimes caused the lower limit of the 95% confidence interval to be negative. In which case, the lower limit of the interval was set to zero.

In situations where the normal distribution approximation to the binomial distribution did not hold, values for the standard error and the 95% confidence interval of estimates were not provided, because these estimates are not reliable.

Note: The asthma prevalence data presented were extracted from the The Centers for Disease Control and Prevention (CDC) Asthma Data: Prevalence Tables website. For more technical information, please visit 2010 Asthma BRFSS Technical Information, CDC website.