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Behavioral Risk Factor Surveillance System – Core Asthma Questions
Uses for Asthma Surveillance
Several questions can be addressed using the BRFSS core asthma questions:
Q What is the prevalence of “lifetime asthma” among adults?
Q What is the prevalence of “current asthma” among adults?
Q Are state asthma prevalence rates among adults higher than national averages?
Q Does asthma prevalence among adults vary by age, sex, race, income and/or education?
Q What are the yearly trends in lifetime and current asthma prevalence among adults?
History of BRFSS Data Collection
In 1984, the Centers for Disease Control and Prevention (CDC) established the Behavioral Risk Factor Surveillance System (BRFSS). BRFSS is the nation’s premier system of health surveys that collect state data about U.S. residents regarding their health-related risk behaviors and events, chronic health conditions, and use of preventive services. (http://www.cdc.gov/brfss/factsheets/pdf/BRFSS-History.pdf)
Currently, BRFSS collects data in all 50 states as well as the District of Columbia and three U.S. territories. BRFSS completes more than 400,000 adult interviews each year, making it the largest continuously conducted multi-mode (mail, landline phone, and cell phone) health survey system in the world. (http://www.cdc.gov/brfss/about/index.htm)
BRFSS is administered by Population Health Surveillance Branch, Division of Population Health, National Center for Chronic Disease Prevention and Health Promotion, CDC. More information about BRFSS can be found at: https://www.cdc.gov/brfss/
The BRFSS has three main sections: the core (a fixed core which is asked every year and a rotating core which is asked every other year), optional modules (standardized sets of questions, which are optional to the state), and state-added questions (state-specific questions which states can add at their own discretion).
Before 1999, several states included state-added questions about asthma on their BRFSS questionnaire, but the wording of the questions varied among those states. In 1999, an optional two-question adult asthma module was added to the BRFSS, representing the first effort to systematically collect state-based asthma prevalence data. In 2000, the two questions were included in the core of the BRFSS questionnaire and were asked in all participating states and territories. The two adult asthma prevalence questions will be included in the BRFSS core in future years as well. For each year of BRFSS asthma data, two asthma prevalence measures were constructed. Lifetime asthma is defined as an affirmative response to the question:
“Have you ever been told by a doctor {nurse or other health professional} that you have asthma?”; Current asthma is defined as an affirmative response to that question followed by an affirmative response to the subsequent question “Do you still have asthma?”.
Additionally, in 2001, an 11-question optional asthma module with additional questions for adults and questions related to child prevalence was added to the BRFSS.
In 2002, the adult and child questions were separated; the nine adult asthma questions became the Adult Asthma History module and the two child asthma prevalence questions became the Childhood Asthma module.
In 2005, the ninth question on the adult module, which had asked about taking medication in general, was separated into two questions: one about controller medications and the other about rescue medications. Also in 2005, the Random Child Selection module was added as an additional step before the administration of the Childhood Asthma module and the wording of the child questions changed slightly. (See the Asthma Surveillance Fact Sheet entitled “Behavioral Risk Factor Surveillance System (BRFSS): Optional Asthma Modules” for additional information.)
BRFSS Sampling and Weighting Changes
Since 2011, BRFSS changed the weighting methodology and added cell phone only respondents into public use data files. The new weighting methodology—iterative proportional fitting, also known as “raking”—replaced the post stratification weighting method that had been used with previous BRFSS datasets. In addition to age, gender, and race/ethnicity, raking permits more demographic variables to be included in weighting such as education attainment, marital status, tenure (property ownership), and telephone ownership. Including new variables in the weighting process can reduce the potential for selection bias while increasing representation. Details are provided in the June 8, 2012 issue of the Morbidity and Mortality Weekly Report (MMWR), which highlights weighting effects on trend lines: www.cdc.gov/mmwr/preview/mmwrhtml/mm6122a3.htm.
For data analysis, the 2011 BRFSS data can 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 the BRFSS Frequently Asked Questions document for additional information: https://www.cdc.gov/surveillancepractice/reports/brfss/brfss_faqs.html
Source of Data (How to Access the Data)
Access the survey data and documentation for any BRFSS survey year. The documentation provides technical and statistical information regarding the BRFSS, such as comparability, sample information, and more. For the corresponding annual questionnaires, see the Questionnaires section of this site.
https://www.cdc.gov/brfss/annual_data/annual_data.htm
Accessing the CDC Public Use BRFSS Asthma Prevalence Data:
- Direct your internet browser to https://www.cdc.gov/brfss/data_tools.htm, select “Prevalence Data and Data Analysis Tools”.
- Select your state from the “State” pull-down menu, select “Year”;
- For year 2010 and before, select “Asthma” from the “Category” selection window, after making these selections, click on “Go.
- From 2011 and onward, select “Chronic Health Indicators”, you should now see the two asthma prevalence questions, “Adults who have ever been told they have asthma”, “Adults who have been told they currently have asthma”. Click questions for prevalence rate.
- You should now see weighted current or lifetime prevalence of asthma in your state for the year you selected. The prevalence of reported lifetime asthma is expressed as a percentage in the “Yes” column of the table. Underneath the bold-faced prevalence estimate are 95% confidence intervals around this estimate, and the unweighted number of cases upon which this estimate was based. The pull-down menu in the upper right corner of the screen can be used to produce lifetime asthma estimates by demographic subgroups of your state’s population. This query can be repeated for any year that your state collected BRFSS asthma data.
Accessing BRFSS asthma prevalence tables produced by the APRHB, CDC
The Air Pollution and Respiratory Health Branch (APRHB), National Center for Environmental Health (NCEH), CDC has developed tables of self-reported lifetime and current asthma prevalence for demographic and socioeconomic subpopulations. Adult prevalence tables included all the 50 states and territories; Child tables only included the states and territories that participated in the Childhood Asthma Prevalence Module. Technical information and tables can be found at: https://www.cdc.gov/asthma/brfss/default.htm.
This page contains current and lifetime asthma prevalence estimates for states by sex, age, race, race/ethnicity, education and income. Consult with your state’s BRFSS coordinator to undertake more in-depth analyses of the asthma prevalence data. APRHB can provide additional guidance if necessary. States and territories are also encouraged to use the BRFSS asthma prevalence questions when undertaking health surveys in smaller geographic areas (e.g., cities or counties).
Analysis Standards
The demographic breakdowns to BRFSS asthma data are summarized below.
- Age Categories: Rates can be calculated separately for the 18-34 year age group, by 10-year age intervals for persons aged 35 to 64 (i.e., 25-34, 35-44, 45-54 and 55-64) and separately for the 65 and older age group.
- Sex Categories: Rates can be calculated separately for “male” and “female” categories.
- Race/Ethnicity Categories: Rates can be calculated separately for “White,” “Black,” “Other,” and “Multi” race categories. Rates should then be calculated for “Hispanic,” “White, non-Hispanic,” “Black, non-Hispanic,” “Other, non-Hispanic,” and “Multirace, non-Hispanic” race/ethnicity categories.
- Education Categories: Rates can be calculated separately for “High School, non-graduate,” “High School, graduate,” “Some College,” and “College graduate” categories.
- Annual Household Income Categories: Rates can be calculated separately for “less than $15,000,” “$15,000 to $24,999,” “$25,000-$49,999,” “$50,000-$74,999,” and “greater than or equal to $75,000” categories.
- Time Trends: Rates can be calculated by year if possible. However, keep in mind that since asthma questions were not added to the core BRFSS survey until 2000, states will not be able to calculate standardized trends in asthma prevalence prior to 2000. Since the changes starting from 2011 in weighting methodology and the addition of the cell phone only respondents, the 2011 BRFSS data should be considered a baseline year for onward trend analysis.
In addition to these demographic indicators, states can also cross-tabulate BRFSS data from the asthma modules with other theoretically relevant variables (e.g., obesity, health insurance status, etc.) or modules (e.g., Secondhand Smoke Policy, Indoor Air Quality). Consult with your state’s BRFSS coordinator to undertake more in-depth analyses of the modules. APRHB can provide additional guidance if necessary.
NOTE: Please consider collapsing years or demographic groups, presenting confidence intervals, or suppressing rates and counts, or a combination of these, if sample size is inadequate. Rates and estimates should be calculated when the denominator is based on 50 or more sample cases. This is the minimum required for stability (e.g., a relative standard error >30%) considering error in measurement introduced by sampling designs (https://www.cdc.gov/nchs/data/statnt/statnt24.pdf). For example, if the denominator is based on fewer than 50 sample cases in any particular year, we recommend combining years to achieve denominators with >50 sample cases, and/or estimating trends based on 3-year rolling averages (e.g., calculate a single rate for 2000-2002, then 2001-2003, etc.)
Anticipated Questions and Answers
Q Shouldn’t states use their own BRFSS data instead of the data at the CDC web sites?
A We recommend that all states make some use of the prevalence data query menus discussed above. This will facilitate standardization and the comparability of rates across states. We also encourage the use of these standard demographic breakdowns in any independent analyses that any state may wish to undertake.
Q Is prevalence a good indicator of the severity of asthma?
A Publication of prevalence data does not replace the need for estimation of asthma severity using ED, hospitalization and mortality data.
Q How have other states made legislative and programmatic use of BRFSS data?
A Examples of how states have used BRFSS data can be found at https://www.cdc.gov/brfss/state_info/brfss_use_examples.htm.
State and Federal Contacts and Resources for BRFSS Core Asthma Data
Centers for Disease Control and Prevention (CDC)
National Center for Environmental Health (NCEH)
Asthma and Community Health Branch
General Number: (770) 488-3700
National Center for Chronic Disease Prevention and Health Promotion
Population Health Surveillance Branch – BRFSS
Current contact information for all state BRFSS coordinators: https://www.cdc.gov/brfss/state_info/coordinators
Links to CDC BRFSS data documentation: BRFSS overview and on-line training: https://www.cdc.gov/brfss/index.htm
BRFSS users guide and technical information
