Prevention. Promotion. Protection.

Section Programs

Resources

BRFSS logo

For more information:

Rebecca W. Topol, SM,
Health Survey Lab Manager & BRFSS Coordinator
Telephone: (907) 465-8540
surveylab@alaska.gov

Survey Information

Methodology

The Behavioral Risk Factor Surveillance System (BRFSS) is conducted by the Alaska Division of Public Health in cooperation with the National Centers for Disease Control and Prevention (CDC). It is a monthly telephone survey that utilizes a standard protocol and interviewing methods developed by the CDC.

Sample Design

Although the main purpose of the BRFSS is to estimate the prevalence of behavioral risk factors in the general population, interviewing each person is not economically feasible. Thus, a probability (or random) sample is selected in which all persons have a known chance of selection. The BRFSS in Alaska uses a stratified random sampling design. The Alaska sample is stratified into six regions based on common demographics. An equal number of interviews are conducted from each region, which purposely oversamples the nonurban areas of Alaska.

Sample Size

Each month over 200 Alaska residents age 18 and older are interviewed over the telephone regarding their health practices and day to day living habits, to reach an annual sample size of at least 2,500. The data are collected from January through December, for each year.

For some indicators BRFSS data have been combined with data from a second survey, the Alaska Supplemental BRFSS. This survey was state developed and is funded by the Alaska Tobacco Prevention and Control Program. The survey focuses largely on tobacco use and attitudes.  It has been collected in Alaska since 2004. The Supplemental BRFSS uses the same sample design, data collection methodology, and has the same sample size goal as the BRFSS. Combining the Supplemental BRFSS survey with the BRFSS where possible allows for a larger sample size for analysis and more stable estimates. Also note that when the combined BRFSS or Supplemental BRFSS data are used, estimates will not match those provided by the CDC for those indicators.

Sampling Process

The GENESYS sampling system through Marketing Systems Group provides a random telephone number sample each month. They use a Disproportionate Stratified Sample (DSS) process that is designed to improve the probability that all households in Alaska with telephones have a chance of inclusion in the study.  For DSS, 100 number blocks of telephone numbers are placed into two strata based on the presumed density (high or low) of residential telephone numbers.  One-plus block strata have at least one residential telephone number while zero blocks have none.  The BRFSS sample is drawn from one-plus blocks; zero blocks are not sampled. The one-plus blocks are further divided based on whether the numbers are listed in a directory (listed one-plus block) or not listed (not listed one-plus block).  Numbers in the listed one-plus blocks are sampled at a higher rate than those in the not listed one-plus blocks.  In addition, GENESYS electronically identifies business, non-working, and cell phone numbers through its identification services and has modified its identification services to detect non-working numbers in rural Alaska. This technological adjustment has improved the process and the survey efficiency for Alaska.  Because Alaska has such a low number of active residential lines, the study requires a large phone sample each month to operate successfully.

Survey Instrument

Participation in the BRFSS is random, anonymous and confidential. Respondents are randomly selected from household residents 18 years of age or older. Only those living in households are surveyed, omitting residents of institutions, nursing homes, dormitories and group homes.

The questionnaire has three parts:

  • Core
  • Optional standard modules
  • State-added questions

The core is a standard set of questions asked by all states. It includes questions about current health related perceptions, conditions, and behaviors (e.g., health status, health insurance, diabetes, tobacco use, selected cancer screening procedures, and HIV/AIDS risks) and questions on demographic characteristics.

Optional modules are CDC-supported sets of questions on specific topics that states can choose to add to their survey. State-added questions are developed or acquired by participating states and added to the questionnaire, they are not edited or evaluated by CDC. States are selective with choices of modules and state-specific questions to keep the questionnaires at a reasonable length of around 100 questions or 20-25 minutes.

Each year the states and CDC agree on the content of the core component and possible optional modules. BRFSS protocol specifies that all states ask the core component questions without modification and may elect to add modules and state-added questions. Any new questions proposed as additions to the BRFSS must go through cognitive and field-testing prior to their inclusion in the survey. The practice of utilizing questions from other surveys such as the National Health Interview Survey or the National Health and Nutrition Examination Survey allows the BRFSS to take advantage of cross-comparison between studies.

Data Collection

A staff of college interns and office assistants, each extensively trained using a standardized CDC protocol, conduct the interviews 7 days a week.  The CDC-developed interviewer training is based on seven basic areas: overview of the BRFSS, role descriptions for staff involved in the interviewing process, the questionnaire, sampling, codes and dispositions, survey follow-up and practice sessions. The survey supervisor and coordinator routinely monitor the interviewers for training purposes and quality control.  Data are collected via computer using WinCATI (Windows-based Computer Assisted Telephone Interviewing) software.

While conducting the telephone interview, the interviewer has the script and questionnaire on a computer screen, which is read verbatim. The designated answer of the respondent is selected on the screen. Incorporating edits and skip patterns into the CATI instrument reduces interviewer errors, data entry errors, and skip errors, while reducing respondent burden.

Data Analysis

Data processing is an integral part of the survey process, with collected data sent to CDC during each month of the year. Data conversion tables are developed to read the survey data and associated call history information from the WinCATI software, and to combine the information into the final format specified for the data year. CDC also created and distributes a Windows-based editing program that can perform data validations on properly formatted survey results. This program is used to output lists of errors or warning conditions encountered in the data. These edited reports are produced monthly and corrections are made by the survey supervisor or coordinator after which data files are sent to the CDC electronically. At the end of each survey year, data are compiled and weighted by CDC, and cross tabulations and prevalence reports are prepared using SAS and SUDAAN software. To create the specific at-risk variables, such as binge drinking, several variables from the data file are combined with varying complexity. With the binge drinking example, the results from several questions in the alcohol section are combined to determine if a respondent is considered a binge drinker. The creation of some at-risk variables requires only combining codes, while others require sorting and combining selected categories from multiple variables.

Weighting

Unweighted data are the actual responses of each survey respondent. The data are weighted or adjusted to compensate for the overrepresentation or under-representation of persons in various subgroups. The data are further weighted to adjust the distribution of the sample data so that it reflects the total population of the sampled area.

Data Reporting

Data are analyzed by the CDC for Alaska by gender, race, age, marital status, education, income and employment and standard tables are produced.

Comparisons

All comparisons made to the national BRFSS median are comparisons made to the median prevalence of the 50 states participating in the Behavioral Risk Factor Surveillance System, plus the District of Columbia, Guam, Puerto Rico, and the U.S. Virgin Islands.

Limitations

The BRFSS uses telephone interviewing for several reasons. Telephone interviews are faster and less expensive than face-to-face interviews.

The main limitation of any telephone survey is that people without landline phones cannot be reached and are not represented. In Alaska, about 97% of households have phones[1] with the U.S. average of phone coverage being 97.6%. The percentage of households with a telephone varies by region in Alaska (see Appendix C). In general, persons of lower socioeconomic status are less likely than persons of higher socioeconomic status to have phones and may be under-sampled. With surveys based on self-reported information, the potential for bias must be kept in mind when interpreting results. Survey response rates may also affect the potential for bias in the data. The literature shows that most questions on the core BRFSS instrument are at least moderately reliable and valid and many were reported to be highly reliable and valid.[2]

In recent years, there has been increase number of people who live in “cell phone only” households.[3,4]  Through 2008 these households were not included in the BRFSS as only households with landline telephones are eligible.  For 2009, all states conducted a small cell phone-based BRFSS using a sample of cell phone exchanges.  To date responses from the cell phone survey have not been combined with those from the landline survey.  The estimates in this report are from the landline survey only.

The reliability of a prevalence estimate depends on the actual, unweighted number of respondents in a category or demographic subgroup. Interpreting and reporting weighted numbers that are based on a small unweighted number of respondents can be misleading since the degree of precision for this instrument increases as the sample size increases.

Prevalence estimates are not reported for those categories in which there were less than 50 respondents and/or the 95% confidence interval half-width is greater than 10. Estimates are rounded to the nearest whole percentage when there are less than 500 observations.

Endnotes

[1] Census 2000 Summary File 4 (SF 4)

[2] Nelson, DE, Holtzman D, Bolen J, et al. Reliability and validity of BRFSS measures. Soz Praventivmed. 2001; Vol. 46:suppl.1

[3] Blumberg, SJ, Lukem, JV. Wireless substitution: early release of estimates from the National Health Interview Survey, June – December 2010. National Center for Health Statistics.  Available from www.cdc.gov/nchs/data/nhis/earlyrelease/wireless201106.pdf.  Accessed: June 2011.

[4] Link, MW, Battaglia, MP, Frankel, MR, Osborn, L, Mokdad AH. Reaching the U.S. cell phone generation: comparison of cell phone survey results with an ongoing landline telephone survey. Public Opinion Quarterly. 2007, Vol. 71: No 5, 814-839.