NYSDOH Expanded BRFSS 2009 Frequently Asked Questions

What is the Expanded BRFSS?

The New York State Expanded Behavioral Risk Factor Surveillance System (Expanded BRFSS) is a random digit dialed telephone survey of adults 18 years of age and older. The goal of the Expanded BRFSS is to collect county-specific data on preventive health practices, risk behaviors, injuries and preventable chronic and infectious diseases. Topics assessed by the Expanded BRFSS include tobacco use, physical inactivity, diet, use of cancer screening services and other factors linked to the leading causes of morbidity and mortality. Survey data collection occurred in 58 geographic areas of New York State, including each of the 57 counties outside of New York City and New York City (5 counties) as a single area.

How are participants selected?

Participants are selected randomly by telephone number. Selection is designed to be representative of the non-institutionalized civilian population with landline telephones living in New York State.

How many people participated from each county?

The goal was to complete about 650 interviews in each area. The final number of interviews varies because of the sampling design of the survey and differential response rates. More detailed information on the sampling design is available in the technical brief (available by request).

Who conducted the Expanded BRFSS?

The New York State Department of Health contracted with RTI International, which is responsible for the data collection, sampling, weighting and creation of the statistical reports. RTI International subcontracted with Clearwater Research Inc. for data collection and additional expertise in sample design and data quality control.

Is there technical documentation available regarding survey methods?

A technical brief that describes the sampling design, the handling of missing data, and the weighting of data to be representative of each county and of New York City has been developed (available by request).

How are health indicators calculated?

For each topic, health indicators are based on answers to one or more questions in the survey. The survey results are weighted to more accurately represent the adult population living in each county. Weighting procedures adjust for the differential selection probabilities by race, age and gender. More detailed information on weighting procedures will be available in the technical brief (available by request).

What is a confidence interval?

A confidence interval is a range around a measurement that conveys how precise the measurement is. The measures estimated in the Expanded BRFSS reports are either a proportion or a rate (e.g., the percent of New Yorkers who have health insurance or the diabetes prevalence rate).

Confidence intervals are often seen on the news when the results of polls are released. This is an example from the Associate Press in October 1996:

  • “The latest ABC News-Washington Post poll showed 56 percent favored Clinton while 39 percent would vote for Dole. The ABC News-Washington Post telephone poll of 1,014 adults was conducted March 8-10 and had a margin of error of plus or minus 3.5 percentage points.”
  • Although it is not stated, the margin of error presented here was probably the 95 percent confidence interval. In the simplest terms, this means that there is a 95 percent chance that between 35.5 percent and 42.5 percent of voters would vote for Bob Dole (39 percent plus or minus 3.5 percent).
  • Conversely, there is a 5 percent chance that fewer than 35.5 percent of voters or more than 42.5 percent of voters would vote for Bob Dole. If the telephone poll were conducted 100 times, 95 times the percent of respondents favoring Bob Dole would be within the calculated confidence intervals and five times the percent favoring Dole would be either higher or lower than the range of the confidence intervals.
  • The Expanded BRFSS reports show the 95 percent confidence intervals for all prevalence rates.

What does a confidence interval tell you?

The confidence interval tells you more than just the possible range around the estimate. It also tells you about how stable the estimate is. A stable estimate is one that would be close to the same value if the survey were repeated. An unstable estimate is one that would vary from one sample to another. A wider confidence interval around the estimate indicates more instability. For example, if 5 percent of voters are undecided, but the margin of error of your survey is plus or minus 3.5 percent, then the estimate is relatively unstable. In one sample of voters, you might have 2 percent say they are undecided, and in the next sample, 8 percent are undecided. This is four times more undecided voters, but both values are still within the margin of error for the survey sample.

On the other hand, narrow confidence intervals in relation to the point estimate tell you that the estimated value is relatively stable, i.e., repeated polls would give approximately the same results.

When making comparisons between counties or to statewide results, how do I determine if the differences are statistically significant?

Confidence intervals are similar to margins of error. When the confidence intervals of two estimates of the same indicator from different areas do not overlap, they may be said to be statistically significantly different, i.e., these differences are unlikely related to chance and are considered true differences. If there is any value that is included in both intervals, the two estimates are not statistically significantly different.

Why are some health indicators missing from the tables?

Health indicators are not shown, i.e., suppressed, if they were considered statistically unreliable or when issues of confidentiality exist. Suppression frequently occurred for estimates made for racial and ethnic groups.

How did you decide to suppress some health indicators?

Health indicators are suppressed when there were fewer than ten respondents who answered the question with the same answer, when the number of respondents answering a particular question was fewer than 50, or when the confidence interval was wide enough to suggest the health indicator was not precise or stable.

Why are some statewide health indicators in the Expanded BRFSS different from statewide health indicators reported on the CDC BRFSS website for 2008?

Expanded BRFSS health indicators for New York State as a whole are based on the county level health indicators combined and weighted to represent the entire state. Health indicators reported for New York State BRFSS on the CDC website for 2008 were calculated from an independent sample of adults in New York State.

Are the health indicators in the 2009 Expanded BRFSS reports comparable to those in the 2003 Expanded BRFSS reports?

Health indicators from the 2009 Expanded BRFSS are generally comparable to those from the 2003 Expanded BRFSS. However, the sampling methods were different between the surveys and the questions used in 2003 and 2009 were not always the same. In the 2003 Expanded BRFSS, samples were drawn for 38 geographic areas including some individual counties, each of the five boroughs of New York City and some of the smaller counties grouped together to form areas. In the 2009 Expanded BRFSS, there were 58 separate geographic areas including the 57 counties outside of New York City and New York City (5 counties) as a single area.

Can I request an electronic version of the Expanded BRFSS data sets so I may do my own analysis?

Final Expanded BRFSS data sets will be provided on request following release of county reports and department approval. At that time, applications to request data will be made available.

When will the next Expanded BRFSS be conducted?

There are no plans to conduct another Expanded BRFSS unless the required resources become available.

If I have other questions, whom should I contact?

All questions should be directed to the BRFSS coordinator. You can send an email to brfss@health.state.ny.us or call the BRFSS Coordinator at 518-473-0673.