2000 Adult Asthma Data: Technical Information

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Viewing and Printing Tables and Maps

Be sure your screen colors are set to True Color (24 bit) or greater so that the colors and shadings on the maps are clearly discernable. Maps are also provided in black and white (B/W) for printing on a non-color printer. Maps should be printed in landscape orientation.

Tables are provided in PDF format and can easily be printed in portrait orientation using Adobe Acrobat.

BRFSS Questionnaire

Interviews are conducted in each state among noninstitutionalized civilian adults (18 years of age or older) living in households with a telephone (Chapter 1, page xviii of the BRFSS User’s Guide). Data are taken from responses to the following questions on the year 2000 BRFSS Questionnaire.

Lifetime asthma:
3.1 Did a doctor ever tell you that you had asthma?
(variable name: asthma)

Current asthma:
If the response to 3.1 was Yes, then question 3.2 was asked: Do you still have asthma?
(variable name: asthnow)

Subgroup tables are based on data from the following questions:

Survey Questions, Variable Names and Codes Used in Subgroup Tables
Survey Question Variable name Codes used
10.18 Indicate sex of respondent sex 1 = male
2 = female
10.01 What is your age? age Grouped into:
18-24, 25-34, 35-44,
45-54, 55-64, 65+
10.02 What is your race? orace 1 = white
2 = black
3,4,5 = other
Race/ethnicity – a combination of response to 10.02 and 10.03 Are you of Spanish or Hispanic origin? race 1 = white, non-Hispanic
2 = black, non-Hispanic
3,4,5 = Hispanic
6,7,8 = Other non-Hispanic
10.06 What is the highest grade or year of school completed? educa 1,2,3 = <HS graduate
4 = HS graduate
5 = some college
6 = college graduate
10.08 Is your annual household income from all sources: a.  Less than $25,000? etc. income2 1,2 = <$15,000
3,4 = $15,000-$24,999
5,6 = $25,000-$49,999
7 = $50,000-$74,999
8 = $75,000+

Survey Design and Sample Weights

The survey design is described in the BRFSS User’s Guide Cdc-pdf[PDF – 1.7 MB].

Illinois used a disproportionate sampling method with clusters of size 1 and a split-sample design. The two asthma questions were only asked of half their total sample. Sample weights are assigned, according to BRFSS methodology, to the variable _FINALWT as described in the BRFSS Weighting Formula. For respondents from Illinois, substitute weights provided by the BRFSS staff were merged into the corresponding records in the BRFSS data set in order to properly accommodate the split-sample design used in that state. For this reason, the numbers for Illinois may differ from those in the published MMWR article (Self-Reported Asthma Prevalence Among Adults – United States, 2000. MMWR 2001;50(32):682-686).

Data Analysis

Data Used:

The BRFSS 2000 Survey Data file was used to calculate estimates for all states. As noted above, however, sample weights for Illinois data were adjusted to properly account for the state’s half-sample design.


Prevalence and standard error estimates were calculated using SUDAAN Release 7.5 (Research Triangle Institute, P.O. Box 12194, Research Triangle Park, NC 27709).

Data Management:

Only respondents with values of the variables as described in the table above are included in each prevalence table. Responses of “don’t know/not sure,” “refused” or missing values, were excluded.

For the question “Do you still have asthma?” respondents included only those who answered “Yes” to the question “Did a doctor ever tell you that you had asthma?” (asthma). Responses to the question, “Do you still have asthma?” (asthnow) were subsequently recoded (assigned a value of 2 = No) if the respondent answered “No” to the first question. Otherwise, this variable (asthnow) was unchanged.

Ratio of Adult Self-Reported Current to Lifetime Asthma by State:

The ratio is a survey-based estimate of prevalence of asthma based on those surveyed who responded “Yes” to question 3.1, “Did a doctor ever tell you that you had asthma?” It is not a rate ratio.

Table Conventions:

The “US Total” line of each table excludes Puerto Rico. “US Total,” therefore, designates an estimate for the 50 states and the District of Columbia combined.

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

Washington, D.C., is omitted from the maps. Its area is so small that the map colors and patterns were not discernible

Ranges in all maps (both overall and for subgroups) are based on quintiles of the overall prevalence estimates from year 2000 data. These same ranges will be used in future years to facilitate year-to-year comparison of the maps.

Data Analysis

When sample sizes in cells are less than 50, as they are in some of the subgroup tables, the standard error may be large relative to the prevalence value, leading to a wide 95% confidence interval. Caution should be used in interpreting such “imprecise” estimates of prevalence.

Also, when one or more of the following situations occurred, the indicated solutions were applied:

Possible Situations and the Solutions

table number 2
Situation Solution
1. The normal distribution approximation to the binomial distribution did not apply. 1. Values for the standard error and the 95% confidence interval were not provided.
2. If the normal distribution approximation does apply, it is appropriate to use values of the t-distribution to compute confidence intervals. 2. Two-sided 95% confidence interval values from the t-distribution with (n-1) degrees of freedom (where n is the number of observations for the subgroup) were used.
3. The lower limit of the 95% confidence interval was negative. 3. The lower limit was set to zero.
Page last reviewed: April 24, 2009