2013 Adult Asthma Data: Technical Information

Behavioral Risk Factor Surveillance System (BRFSS) - 2013

BRFSS Survey

In 2013, the BRFSS survey was conducted in all 50 states and 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. Asthma prevalence data are produced from the responses to two asthma questions on the year 2013 BRFSS Core Questionnaire.

Lifetime asthma: Question number 7.4

Has a doctor, nurse, or other health professional ever told you had any of the following: (Ever told) you had asthma? (variable name: ASTHMA3)

The calculated variable _LTASTH1 (based on question 7.4) from the BRFSS public use file was used when creating the tables.

Current asthma: Question number 7.5

If the response to 7.4 was Yes, then question 7.5 was asked: Do you still have asthma? (variable name: ASTHNOW)

The calculated variable _CASTHM1 (based on questions 7.4 and 7.5) from the public use file was used when creating the tables.

BRFSS Sampling and Weighting Changes

The 2011 BRFSS data collection changed from a landline only sample to a dual-frame survey, landline and cellphone. The 2013 BRFSS data continues to reflect the changes initially made in 2011 in weighting methodology (raking) and the addition of cell phone only respondents. The aggregate BRFSS combined landline and cell phone dataset is built from the landline and cell phone data submitted for 2013 and includes data for 50 states, the District of Columbia, Guam, and Puerto Rico. More information about the changes to the 2011 BRFSS can be found at the CDC Surveillance Resource Center.

For data analysis, the 2011 BRFSS data should be considered a baseline year and are not directly comparable to previous years of data because of the changes in weighting methodology and the addition of the cell phone only respondents. Please see BRFSS Comparability of Data for additional information.

Data Analysis

Data Used:

The BRFSS 2013 Survey Data file was used to calculate estimates for all states.


The BRFSS 2013 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 11.1 (Research Triangle Institute, P.O. Box 12194, Research Triangle Park, NC 27709).

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:

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.

Table Conventions:

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.

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 t equals the z distribution value of 1.96 for state level prevalence in the Table titled "Overall Adult Asthma Prevalence in The US and New York State - 2011 BRFSS". 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.

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
  • Education: HS Nongrad(less than High School graduate), HS Grad, Some Coll(College), and Coll Grad
  • Income: $0-$14,999, $15,000-$24,999, $25,000-$49,999, $50,000-$74,999, and $75,000+

Small Sample Size Assumptions

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.

Note: The asthma prevalence data presented were extracted from the The Centers for Disease Control and Prevention (CDC) Asthma Data: Prevalence Tables and Maps website. For more technical information, please visit 2013 Asthma BRFSS Technical Information, CDC website.