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Technical Notes 2011

Behavioral Risk Factor Surveillance System (BRFSS)

Detailed data tables for NC BRFSS survey items are posted by the SCHS on an annual basis. The exact wording for each question is used as a title for the majority of the web tables, however due to space limitations the titles may not include some introductory remarks and explanations for some questions. Although not all survey questions are presented in the web tables, the full questionnaire may be viewed online.

For the majority of survey items, the results are displayed by sex, race, age, education and household income. For the statewide and regional tables, disability status, veteran status and Hispanic origin are also displayed as demographic groups.

Results are also posted separately by gender, by race (white and African American), and by selected risk factors (defined below). In addition, the results are posted for 23 of the state's largest counties. For 2011, if the total number of respondents was less than 100 for a particular survey item, the results were limited to the total sample and further subgroups are not presented. This occurred most often for county-level tables regarding topics, such as diabetes, that pertained to a small sample of respondents. As was the case in 2009 and 2010, the results for gender by race, e.g., white females, have not been posted for 2011. These results may be obtained by request by contacting the BRFSS staff.

Changes to the BRFSS Survey Methodology

Beginning in 2011, the Division of Behavioral Surveillance (DBS) of the Centers for Disease Control and Prevention made two major changes to the BRFSS Survey methodology. These changes were designed to improve the accuracy of BRFSS estimates; however the results using these new methods are not comparable to BRFSS estimates from previous years1.

The first change is the adoption of an improved weighting method called iterative proportional fitting, commonly referred to as “raking.”  Raking is a technique for weighting the survey data, whereby the weighted respondent data is made more comparable to the characteristics of the target population, such as the proportion of Hispanic adults in the state.  Raking improves the representativeness of state estimates by including socio-economic factors, such as education and marital status, in the final survey weights.  The former post-stratification methodology, was limited to adjusting the final weights by categories of age, race and sex and is no longer utilized.

The second change is the addition of cell phone interviews to the BRFSS. Adoption of cell phones (with no landline phone) has been particularly evident among younger adults and racial/ethnic minorities. Adding cell phone interviews improves the BRFSS coverage of these groups.

As a result of these changes, the BRFSS will better represent lower-income and minority populations and provide more accurate prevalence estimates. However, it will no longer be possible to compare results from 2011 or later BRFSS surveys to results from earlier years of BRFSS data.  It is also likely that prevalence estimates will be somewhat higher as a result of the change in methods for behaviors that are more common among younger adults and/or minorities.

Interpreting Results

For several years the CDC BRFSS program has suppressed prevalence estimates which did not met minimal criteria for statistical reliability based on sample size and the width of the confidence intervals. To better meet our goal of providing high quality health information for better informed decisions and effective health policies, the SCHS has adopted this practice for our 2011 BRFSS web tables.

We suppressed prevalence estimates when any of the following criteria were met:

  1. There were fewer than 10 respondents in the numerator (i.e. the number of respondents associated with the response categories, e.g. “Yes”, “No”).
  2. There were fewer than 50 respondents in the denominator (i.e. the table column labeled "Total Respond”).
  3. The width of the confidence interval for the prevalence estimate was greater then 20.

Some topics are age-dependent, such as prostate cancer screening, which was asked only of men 40 years or older. Please note age ranges for particular survey items in the web table’s footnotes or as cited in the table title.

Weighted BRFSS data are used in all calculations; therefore percentages shown in web tables cannot be derived from the numbers presented. BRFSS data are weighted for the probability of selection of a telephone number, the number of adults in a household, and the number of phones in a household and adjusted to reflect the demographic distribution of North Carolina's adult population (ages 18 and older).

Respondents who refused to answer or did not know the answer were excluded from most calculations in these tables. However, there are instances when "Don't know/Not sure" responses may provide valuable information and are included in the response categories.

For more technical information about BRFSS, please visit national BRFSS web site.

Change in Disability Status

The definition for disability status has changed beginning with our 2011 BRFSS web tables. In October 2011, the U.S. Department of Health & Human Services (DHHS) issued new standards for the collection of disability information2. The use of these standards is now required on all federally-funded population surveys. The disability data collection standards were designed to improve health surveillance by allowing researchers to consistently monitor disability across federal surveys. These changes also allow North Carolina to compare our disability data with the rest of the U.S.

Thus, 2011 will become the year to re-benchmark our definition of disability. The data collection standards now include two disability questions that will comprise North Carolina’s definition of disability: 1) Respondents that reported being limited due to physical, mental or emotional problems or 2) Respondents who reported that they have a health problem that requires the need for special equipment.

Risk Factors and Calculated Variables Presented in the 2011 BRFSS Results

Body Mass Index Grouping

Body mass index (BMI) is computed as weight in kilograms divided by height in meters squared:(kg/ m2). BMI is an intermediate variable used in calculating these measures:
Underweight: BMI less than 18.5, Recommended Range: BMI 18.5 to 24.9, Overweight: BMI 25.0 to 29.9, Obese: BMI greater than 29.9. and Overweight or Obese: BMI greater than 24.9.

Health Insurance Coverage - Age Under 65

Yes: All respondents less than age 65 who answered YES to the Core question on having any kind of health (HLTHPLN1). Respondents with missing age were excluded.
No: All respondents less than age 65 who answered NO to the Core question on having any kind of health (HLTHPLN1). Respondents with missing age were excluded.

Health Insurance Coverage for Those Employed for Wages (Age under 65)

Yes: All respondents less than age 65 who answered YES to the Core question on having any kind of health (HLTHPLN1), and answered “yes” to being employed for wages. Respondents with missing age were excluded.
No: All respondents less than age 65 who answered YES to the Core question on having any kind of health (HLTHPLN1), and answered something OTHER then “yes” to being employed for wages. Respondents with missing age were excluded.

Smoking Status

Current Smoker (every day): Respondents who have smoked at least 100 cigarettes in their lifetime and now smoke every day.
Current Smoker (some days): Respondents who have smoked at least 100 cigarettes in their lifetime and now smoke some days.
Former Smoker: Respondents who have smoked at least 100 cigarettes in their lifetime and currently do not smoke.
Never Smoked: Respondents who have not smoked at least 100 cigarettes in their lifetime.

Current Smoker

Yes: Current Smoker (every day or some days)
No: Former Smoker or Never Smoked.

Binge Drinking

No : Respondents who report they did not drink in the past 30 days, or who drank in the past 30 days but did not have five or more drinks for males or four or more drinks for females on an occasion.
Yes : Respondents who report they did drink in the past 30 days and had five or more drinks for males or four or more drinks for females on one or more occasions in the past month.

Heavy Drinking

Yes: Respondents reported having MORE than 2 drinks/day for MALES and MORE than 1 drink/day for FEMALES.
No: Respondents reported having LESS than or equal to 2 drinks/day for MALES and LESS than or equal to 1 drink/day for FEMALES.

County-level Results

Considering the data suppression rules that went into affect this year, and considering the potential for small numbers at the county-level, there are some questions or modules that will not feature any county-level data, including the top row of data. The following is an example of total suppression of county-level data. In this case, only the state totals are shown. If there are less than 50 respondents in total, all county data is suppressed.

2011 BRFSS Survey Results: Alamance County

Following your heart attack, did you go to any kind of outpatient rehabilitation?* This is sometimes called rehab.

Total
Respond.^

Yes

No

N

%

C.I.(95%)

N

%

C.I.(95%)

North Carolina

623

240

36.6

30.8-42.8

383

63.4

57.2-69.2

DUE TO SMALL NUMBERS, COUNTY-LEVEL RESULTS ARE NOT AVAILABLE.

 

Strengths and Limitations of the BRFSS Survey Data

One limitation of a telephone survey is the lack of coverage of persons who live in households without a telephone. Households without a telephone are, on average, of lower income. Therefore, for many of the health risks measured, the results are likely to understate the true level of risk in the total population of adults in North Carolina. A second limitation is due to the fact that the data are self-reported by the respondents. We expect that respondents tend to underreport health risk behaviors, especially those that are illegal or socially unacceptable. A third limitation is that these data are “cross-sectional,” meaning that the data are collected in a single point in time. Each month an entirely new sample of respondents are contacted. Therefore, causality cannot be inferred from BRFSS survey results.  All that can be determined is the likelihood of an association between two or more variables, such as the association between smoking and cardiovascular disease – these results do not permit one to say that smoking “causes” heart disease.

There are some significant advantages of the telephone survey methodology, including better quality control over data collection made possible by a computer-assisted-telephone-interviewing system, relatively low cost, and speed of data collection. The BRFSS methodology has been used and evaluated by the CDC and participating states since 1984. The content of the survey questions, questionnaire design, data collection procedures, interviewing techniques and editing procedures have been carefully developed to improve data quality and lessen the potential for bias. The data collection is ongoing, and each year new annual results become available.

 

1 Pierannunzi, C., Town, M., Garvin, W., Shaw, F and Balluz, L. Methodologic Changes in the Behavioral risk Factor Surveillance System in 2011 and Potential Effects on Prevalence Estimates. Morbidity and Mortality Weekly Report; 2012 June;61(22):410-413. Available at http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6122a3.htm?s_cid=mm6122a3_w. Accessed September 12, 2012.

2 U.S. Department of Health and Human Services. Implementation Guidance on Data Collection Standards for Race, Ethnicity, Sex, Primary Language, and Disability Status. Available at: http://aspe.hhs.gov/datacncl/standards/ACA/4302/index.shtml. Accessed September 17, 2012.

Return to 2011 BRFSS Annual Results Table of Contents