2001 Adult Asthma Data: Technical Information
Viewing and Printing Tables and Maps
The view option for your browser should be set to the smallest available text size to ensure that columns of numbers are properly formatted and that part of the page is not lost when printing.
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) if a color printer is not available. Maps should be printed in landscape orientation.
Tables are provided in both HTML and PDF format. The PDF files will load more quickly, but cannot be used with ADA assisted technology. Tables printed in portrait orientation using Adobe Acrobat may produce more pleasing results than printing the HTML-formatted tables.
In 2001, 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 are conducted, respondents are randomly selected from noninstitutionalized civilian adults (18 years of age or older) living in households with a telephone (Chapter 1, page xviii of BRFSS User's Guide [PDF - 1.7 MB]). Asthma prevalence data are produced from the responses to two asthma questions on the year 2001 BRFSS Core Questionnaire.
6.1 Have you ever been told by a doctor, nurse, or other health professional that you had asthma? (variable name: asthma2)
If the response to 6.1 was Yes, then question 6.2 was asked: Do you still have asthma? (variable name: asthnow)
Subgroup tables are based on data from the following questions:
|Survey Question||Variable name||Codes used|
|13.16 Indicate sex of respondent||sex||1 = male|
2 = female
|13.1 What is your age?||age||Grouped into:|
18-24, 25-34, 35-44,
45-54, 55-64, 65+
|13.2 Are you Hispanic or Latino?||hispanc2||1 = yes|
2 = no
|13.3 Which one or more of the following would you say is your race?||_mrace||1 = white|
2 = black or African American
3 = Asian
4 = Native Hawaiian, Pacific Islander
5 = American Indian, Native Alaskan
6 = other race
7 = multiracial
|Responses to 13.2 and 13.3 are used to define race/ethnicity||_racegr2||1 = white, non-Hispanic|
2 = black, non-Hispanic
3 = other, non-Hispanic
4 = multiracial, non-Hispanic
5 = Hispanic
|13.7 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
|13.9 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 technical pages document, entitled, "2001 Overview" at http://www.cdc.gov/brfss/annual_data/annual_2001.htm. Sample weights are assigned, according to BRFSS methodology, to the variable _FINALWT as described in the BRFSS Weighting Formula.
The BRFSS 2001 Survey Data file was used to calculate estimates for all states.
Prevalence and standard error estimates were calculated using SUDAAN Release 9.0 (Research Triangle Institute, P.O. Box 12194, Research Triangle Park, NC 27709).
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 question 6.1, “Did a doctor ever tell you that you had asthma?” (asthma2). Responses to question 6.2, “Do you still have asthma?” (asthnow) were subsequently recoded (assigned a value of 2 = No) if the respondent answered “No” to question 6.1. 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 6.1, “Did a doctor ever tell you that you had asthma?” It is not a rate ratio.
The 95% Confidence Intervals were calculated using the following formulae:
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 t equals the z distribution value of 1.96 for state level prevalence in Table 1. For other tables with smaller sample sizes due to the use of demographic subcategories, the exact value from the t distribution appropriate to the sample size for the percent prevalence was used instead of the approximate z-value of 1.96. Because of the use of the more exact t-value, 95% Confidence Intervals in the tables may differ slightly from those presented in other representations of these data.
The “US Total” line of each table excludes Puerto Rico, Guam and the Virgin Islands. “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.
The chart presents the state and territory prevalence percents from Table 1 sorted from high to low. Confidence intervals are also represented graphically for each prevalence value. Overlapping confidence intervals for two states is a rough indication that state prevalence values are not significantly different from one another.
Small Sample Size
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:
|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.|