2006 Child Asthma Data: Technical Information

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Behavioral Risk Factor Surveillance System (BRFSS) Survey

In 2006, the BRFSS survey was conducted in all 50 states, the District of Columbia and in two US territories (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 - 1.7 MB]).

Child asthma prevalence data are produced from the responses to questions on BRFSS Random Child Selection and Childhood Asthma optional modules. The 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-five states, the District of Columbia and one territory used both the BRFSS Random Child Selection and Childhood Asthma optional modules in 2006. However, two states, Oregon and Connecticut, which did use both Random Child Selection and Childhood Asthma optional modules in their respective surveys, did not have the appropriate child weight data. Therefore these two states were not included in the 2006 BRFSS analysis. The states and territories that were used in the asthma prevalence analysis were

Alaska, Arizona, California, District of Columbia, Georgia, Hawaii, Idaho, Indiana, Iowa, Kansas, Kentucky, Maine, Maryland, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, Nevada, New Hampshire, New Jersey, New York, Ohio, Oklahoma, Pennsylvania, Rhode Island, Texas, Utah, Vermont, Virginia, West Virginia, Wisconsin, Wyoming, 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 3.1
“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 3.2
“Does the child still have asthma?” (Variable name: CASTHNO2 [Yes = 1 / No = 2])

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

Survey Questions, Variable Names and Codes Used in Subgroup Tables

Survey Design and Sample Weights

The survey design and the child-weighting methods are described in the technical document, “Overview: BRFSS 2006”, which can be found at the following Web location: http://www.cdc.gov/brfss/technical_infodata/surveydata/2006/overview_06.rtf.

Data Analysis

Data Used:

The BRFSS 2006 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.

Software:

Prevalence and standard error estimates were calculated using SAS callable SUDAAN Release 10.0.0 (Research Triangle Institute, Research Triangle Park, NC).

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 and Prevalence Numbers:

The 95% confidence intervals were calculated using the following formulas:

Lower 95% confidence interval = % prevalence – t_v (se_p)
Upper 95% confidence interval = % prevalence + t_v (se_p)

Where se_p is the standard error of the prevalence percent and t_v represents the student’s t distribution with v degrees of freedom.

Small Sample Size and Failure of Distributional Assumptions

When sample sizes for a particular state or territory was 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.

Table Conventions:

In the tables, states and territories are listed in Federal Information Processing Standard (FIPS) code order.