Behavioral Risk Factor Surveillance System (BRFSS)
Florida is one of 50 states conducting the Behavioral Risk Factor Surveillance System (BRFSS) with financial and technical assistance from the Centers for Disease Control and Prevention (CDC). This state-based telephone surveillance system is designed to collect data on individual risk behaviors and preventive health practices related to the leading causes of morbidity and mortality in the United States. Information from the survey is used for health planning, program evaluation, and monitoring health objectives within the Department of Health. Target population of BRFSS are people 18 years and older, who reside in a Florida household. In Florida, BRFSS started in 1986. Since then, it has been conducted annually. Sample Size and Response Rate, 1986-2010
Junwei Jiang, MPH
Tel: (850) 245-4444 ext. 2445
- About BRFSS Questionnaires
- Sampling and Weighting Methods
- Data Analysis and Collection
- What Can the DOH Provide?
The BRFSS questionnaire is jointly developed by CDC and state. Core questions are provided by CDC, and states are asked not to make any changes to these questions. Rotating core questions are those questions asked every other year. The emerging core is a set of questions, also called a test module, that typically focus on issues of a "late breaking" nature and are evaluated at the end of one year to determine their potential value in future surveys. The BRFSS also includes optional modules provided by CDC, which are sets of questions on selected topics. States may choose to add any of the modules. States can add their own original questions. Available Modules 1986-2014
Florida is using the disproportionate stratified sampling (DSS) from the 1999 survey. In DSS, phone numbers were drawn from two sets of telephone number blocks, and one adult is selected from one telephone number (Flow chart of DSS: http://www.floridashealth.com/reports-and-data/survey-data/behavioral-risk-factor-surveillance-system/_documents/DSS-flowchart.jpg). First, CDC purchases a list of randomly selected telephone numbers and provides it to each state. Then, as you can see from the flow chart, there are standard procedures to follow. If there is no answer, the interviewer redials up to 15 times across a period of time. If interviewer reaches a nonworking number or a business, calls to that number stop. If the interviewer reaches a household with more than one adult 18 or older, one of them is randomly selected for the interview.
Prior to 2003, the Florida sample was stratified by seven regions, which were groups of counties that were contiguous but otherwise might have little in common with each other. From 2003 through 2006, Florida used three strata groups based on county population size: small (less than 50,000), medium (50,000-299,999) and large (300,000 or more), and a fourth stratum was added from 2004 through 2006 that sample areas with telephone exchanges that are known to have at least 45% minority households. In 2007 and 2010, the Florida sample has been stratified by county to ensure more useful estimates at the local level.
After the data collection is completed, data is cleaned and weighted by CDC. Data weighting is an important statistical process that attempts to remove bias in the sample. BRFSS data set is weighted by density status, geographic region, number of residential telephone numbers, number of adults, age, gender and race/ethnicity.
As we have seen so far, BRFSS is not based on simple random sampling. Because of this fact, we recommend that SAS/SUDAAN software be used to conduct data analysis. Confidence intervals are an important measures of the role of chance.
BRFSS data is collected by calendar year. Since 2000, the Florida Department of Health has contracted out the BRFSS data collection to a survey company. Data are collected through monthly telephone interviews, and the Department of Health regularly monitors interviews to maintain and ensure data quality. At the completion of the interviewing cycle each month, the survey company sends the data to CDC. At the end of the year, the CDC aggregates monthly data for the entire year. The Department of Health usually receives the annual dataset from the CDC in late spring following the survey administration year.
There is no charge to use BRFSS data. The data request form is available in this site. We can also provide technical assistance for those interested in conducting their own data analysis with SAS or SUDAAN. Prevalence data for the major questions is available at CDC BRFSS website at http://www.cdc.gov/brfss/. At this website, you can view the estimated prevalences with 95% confidence intervals by demographic break down such as age gender race/ethnicity and socioeconomic status.