Methodology for State-Level Estimates
 

Data Source

Estimates were calculated using data from CDC's Behavioral Risk Factor Surveillance System (BRFSS). The BRFSS is an ongoing, state-based telephone survey of the adult population of states.^1,2 The survey provides state-specific information on behavioral risk factors and preventive health practices.

Diabetes prevalence and incidence

Respondents were considered to be prevalent cases of diabetes if they responded "yes" to the question, "Has a doctor, nurse or other health professional ever told you that you have diabetes?" Women who indicated that they only had diabetes during pregnancy were not considered to have diabetes. We calculated the prevalence rate by dividing the weighted number of prevalent cases by the total number of persons.

Prevalent cases of diabetes were asked at what age they were diagnosed. We calculated the number of years each person had been diagnosed with diabetes by subtracting the age at which they were diagnosed from their current age. Adults who had a value of zero were identified as having been diagnosed with diabetes within the last year. In addition, half of the adults who had a value of one were classified as having been diagnosed with diabetes within the last year. To calculate incidence, the numerator was the weighted number of adults who were diagnosed with diabetes within the last year and the denominator was the weighted estimate of adult population, excluding adults who had been diagnosed with diabetes for more than one year and adults who answered "refused," "don’t know," or had missing values on the diabetes status question.

Diagnosed diabetes prevalence was calculated among adults aged 18 years and older. Prevalence estimates are based on single years of data. Diabetes incidence was calculated among adults aged 18 to 76 years. Incidence estimates are 3-year averages. The 2000 U.S. population was used as the standard for age adjustment for prevalence and incidence.

Top of Page

Physical Inactivity and Obesity

Adults who reported not participating in physical activity or exercise in the past 30 days were considered to be physically inactive. Self-reported weight and height were used to calculate body mass index (BMI): weight in kilograms divided by the square of height in meters. A BMI greater than or equal to 25 was considered to be overweight or obese, a BMI of greater than or equal to 30 was considered to be obese.

Estimates of physical inactivity and obesity were calculated among adults aged 18 years and older. Estimates are based on single years of data. The 2000 U.S. population was used as the standard for age adjustment.

Prior to year 2000, the physical inactivity question was rotated in and out of the core BRFSS questionnaire. When not part of the BRFSS core in odd years, the physical inactivity question was part of an optional BRFSS module. As a result, only a few states have physical inactivity data for years 1995, 1997, and 1999. Beginning in 2000, the physical inactivity question no longer rotated off the BRFSS core.

Top of Page

Data Limitations

Persons residing in nursing homes and in households without telephones are not included in this survey; therefore, these results cannot be generalized to those segments of the population. Because the BRFSS is a telephone survey, bias may be introduced because households without telephones are not included. Although telephone coverage is generally high, non-coverage may be high for certain population groups. For example, American Indians, rural blacks in some southern states, and persons in lower socioeconomic groups typically have lower telephone coverage (1,3,4). All data in the BRFSS are obtained by self-report and are subject to recall bias or may be underreported or overreported. Self-report of diagnosed diabetes, physical inactivity and sociodemographic characteristics are highly accurate (5-7).However, about one-third of persons with diabetes do not know they have it.⁸ Reliance on self-reported heights and weights to calculate the BMI is likely to underestimate average BMI and the proportion of the population in higher BMI categories in population surveys.⁹

Excel files with county estimates for the entire nation and for each state are available for downloading. Click on the Download Data button then select an indicator. Next, you will select either the nation, which contains data for all the states, or individual state data that you want to download. The files are saved in XML format but can be easily opened and viewed in Excel. If you wish to import the data into statistical software, you will need to save the XML file as an XLS file in Excel.

Top of Page

1. Centers for Disease Control and Prevention. Survey methodology. In: Behavioral Risk Factor Surveillance System Operational and User's Guide. Atlanta: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention; 2006. ftp://ftp.cdc.gov/pub/Data/Brfss/userguide.pdf [PDF–986KB] Accessed October 10, 2012.

2. CDC. Health Risks in the United States. Behavioral Risk Factor Surveillance System: At a glance, 2010 Web site. http://www.cdc.gov/chronicdisease/resources/publications/AAG/brfss.htm. Accessed October 10, 2012.