2009 Child Asthma Data: Technical Information

Behavioral Risk Factor Surveillance System (BRFSS) - 2009

BRFSS Survey

In 2009, 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 (Chapter 4, page 7 of the BRFSS User's Guide [PDF - 986 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-seven states or territories used both the BRFSS Random Child Selection and Childhood Asthma optional modules in 2009. These states or territories were

California, Connecticut, Delaware, District of Columbia, Georgia, Hawaii, Idaho, Illinois, Indiana, Iowa, Kansas, Louisiana, Maine*, Maryland, Massachusetts*, Michigan, Mississippi, Montana, Nebraska, Nevada, New Jersey, New Mexico*, New York, North Dakota, Ohio*, Oklahoma*, Oregon*, Pennsylvania, Rhode Island, Texas, Utah, Vermont, Virginia, Washington, West Virginia, Wisconsin, and 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 26.1

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 26.2

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

Data Analysis

Data Used:

The BRFSS 2009 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. For states that used one or more dual questionnaires for these two modules, questionnaire version specific datasets were used for analysis.


The BRFSS 2009 survey data file was used to analyze lifetime and current asthma prevalence by selected sociodemographic groups. Prevalence and standard error estimates were calculated using SUDAAN Release 10.0.0 (Research Triangle Institute, P.O. Box 12194, Research Triangle Park, NC 27708).

Number of people affected was estimated by multiplying the prevalence rate against the US or New York State population in that particular subgroup.

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 – t(sep)
  • Upper 95% Confidence Interval = % prevalence + t(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, Other, and Multi Race
  • Race/Ethnicity:White NH(non-Hispanic), Black NH, Other NH, Multirace 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 2009 Asthma BRFSS Technical Information, CDC website.