2005 Child Asthma Data: Technical Information
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Behavioral Risk Factor Surveillance System (BRFSS) Survey
In 2005, the BRFSS survey was conducted in all 50 states 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.
Twenty-three states and one territory used both the BRFSS Random Child Selection and Childhood Asthma optional modules in 2005. These states and territories were:
Arizona, Connecticut, Hawaii, Idaho, Indiana, Iowa, Kansas, Maryland, Michigan, Minnesota, Montana, New Hampshire, New Jersey, New Mexico, Ohio, Oregon, Pennsylvania, Rhode Island, South Dakota, Vermont, Virginia, 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 11.1
“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 11.2
“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
10.1 What is the birth month and year of the “Xth” child?
IDATE: Date of interview
RCSBIRTH: The birth date, month and year of the “Xth” child. (The birth date is chosen as the 15th of the birth month)
Age of the Child in years is calculated as: (IDATE – RCSBIRTH)/365.25.
|10.2 Is the child a boy or a girl?||
2 = Girl
|10.3 Is the child Hispanic or Latino?||
2 = No
|10.4 Which one or more of the following would you say is the race of the child?|
Survey Design and Sample Weights
The survey design and the child-weighting methods are described in the technical document, “Overview: BRFSS 2005”, which can be found at the following Web location: http://www.cdc.gov/brfss/technical_infodata/surveydata/2005/overview_05.rtf.
The BRFSS 2005 survey dataset was used to calculate prevalence estimates.
Prevalence and standard error estimates were calculated using SAS callable SUDAAN Release 10.0.0 (Research Triangle Institute, Research Triangle Park, NC).
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 – 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.
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.
In the tables, states and territories are listed in Federal Information Processing Standard (FIPS) code order.