Skip directly to search Skip directly to A to Z list Skip directly to navigation Skip directly to site content Skip directly to page options
CDC Home

Frequently Asked Questions (FAQ)

National and State Surveillance Data

Top of Page

County Level Estimates Maps

Top of Page

Data Sources and Methodology for County-Level Estimates of Diagnosed Diabetes and Selected Risk Factors

Top of Page

How to Read the Maps of County-Level Estimates of Diagnosed Diabetes and Selected Risk Factors

Top of Page

Methodology for Mapping County-Level Estimates of Diagnosed Diabetes and Selected Risk Factors

Top of Page

County Level Estimates Maps
 

Where can I find the most current U.S. county-level estimates?

The Diabetes Interactive Atlases provide the most current county-level estimates of diagnosed diabetes, obesity, and leisure-time physical inactivity in the United States.

Top of Page

Data Sources and Methodology for County-Level Estimates of Diagnosed Diabetes and Selected Risk Factors
 

What method was used to create county-level estimates?

The prevalence of diagnosed diabetes and selected risk factors by county was estimated using data from CDC's Behavioral Risk Factor Surveillance System (BRFSS) and data from the U.S. Census Bureau’s Population Estimates Program.1 The BRFSS is an ongoing, monthly, state-based telephone survey of the adult population. The survey provides state-specific information on behavioral risk factors and preventive health practices. Respondents were considered to have diabetes if they responded "yes" to the question, "Has a doctor ever told you that you have diabetes?" Women who indicated that they only had diabetes during pregnancy were not considered to have diabetes. Respondents were considered obese if their body mass index was 30 or greater. Body mass index (weight [kg]/height [m]2) was derived from self-report of height and weight. Respondents were considered to be physically inactive if they answered "no" to the question, "During the past month, other than your regular job, did you participate in any physical activities or exercises such as running, calisthenics, golf, gardening, or walking for exercise?"

Three years of data were used to improve the precision of the year-specific county-level estimates of diagnosed diabetes and selected risk factors. For example, 2003, 2004, and 2005 were used for the 2004 estimate and 2004, 2005, and 2006 were used for the 2005 estimate. Estimates were restricted to adults 20 years of age or older to be consistent with population estimates from the U.S. Census Bureau. The U.S. Census Bureau provides year-specific county population estimates by demographic characteristics—age, sex, race, and Hispanic origin.

The county-level estimates for the over 3,200 counties or county equivalents (e.g., parish, borough, municipio) in the 50 U.S. states, Puerto Rico and the District of Columbia were based on indirect model-dependent estimates.2-4 The model-dependent approach employs a statistical model that “borrows strength” in making an estimate for one county from BRFSS data collected in other counties. Bayesian multilevel modeling techniques were used to obtain these estimates. Separate models were developed for each of the four census regions: West, Midwest, Northeast and South. Multilevel Poisson regression models with random effects of demographic variables (age 20–44, 45–64, 65+; race; sex) at the county-level were developed. State was included as a county-level covariate. The model specification is essentially the same as Malec, et al.3

For selected years, rates were age adjusted by calculating age specific rates for the following three age groups, 20-44, 45-64, 65+. A weighted sum based on the distribution of these three age groups from the 2000 census was then used to adjust the rates by age. The weights used were as follows: 0.52, 0.31, 0.17.

Ranks for county-level data of diagnosed diabetes and selected risk factors were based on age-adjusted prevalence rates. Models were fit using a Bayesian simulation method known as Markov Chain Monte Carlo.2-4 As part of the model fitting process we generated and saved two thousand draws from the distribution of each county's age-adjusted prevalence rate. For each of these draws we sorted the counties by prevalence and saved the counties' ranks. This gave us two thousand draws from the distribution of each county's rank. We then used the median for the rank estimate and the 5th and 95th percentiles for a 90% confidence interval.

Top of Page

Are the same types of data available for all years?

County-level estimates including age-adjusted rates and rankings are available for all years beginning in 2004 to the current year of available data. However, only data for diagnosed diabetes prevalence is available for Puerto Rico municipios from 2004 to the current year of available data.

Top of Page

Can I download the map data of county-level estimates?

Excel files with county estimates for the entire nation and for each state are available for downloading. Under County Level Estimates (National Maps), the link to download the national data is located below the national map, and under County Level Estimates (State Maps), the link to download the state data is located in the Options and Tools box above each state map.

Top of Page

Where are the definitions of variables that are found in the downloadable dataset of county-level estimates?

The national-level and state-level variables with definitions are located in the Data Dictionary, shown as a link beside each downloadable file. Under County Level Estimates (National Maps), the link to the downloadable file is located below the national map, and under County Level Estimates (State Maps), the link to the downloadable file is located in the Options and Tools box above each state map. Variables found in the national and state datasets are the same.

Top of Page

How to Read the Maps of County-Level Estimates of Diagnosed Diabetes and Selected Risk Factors
 

How do I access the various types of maps available?

Both national-level and state-level views are available for county estimates. For national-level view, click on County-Level Estimates (National Maps) on the Diabetes Data and Trends homepage. For state-level view, you can obtain county estimates through the Diabetes Data and Trends homepage or the County-Level Estimates (National Maps) homepage. On the Diabetes Data and Trends homepage, click the link State Maps under County Level Estimates, then select the state of interest from the drop down menu State and click GO. You can also select your state of interest on the Diabetes Data and Trends homepage from the drop-down menu under State Surveillance Data including County Maps and then click GO, or click directly on the state on the U.S. map. On the County-Level Estimates (National Maps) homepage, you must select your state of interest from the drop-down menu County Level Estimates—State Maps at the bottom of the page and then click GO.

Top of Page

What factors do I need to choose to display a map?

For national maps of county-level estimates, select a State, Indicator (e.g., diagnosed diabetes), Year, Data Type (Percent of Adults, Age-adjusted Percent of Adults, Number of Adults, Percent by Number of Adults, Low/High Median Rank), and Classification (trends, quartiles), and then click GO. For state maps of county-level estimates, select an Indicator, Year, Data Type, and Classification and then click GO. See the next question if interested in looking at trends using these maps. For the definition of quartiles, see the glossary.

Top of Page

How can I use the maps to look at trends?

Under the drop-down menu Classification in either the County Level Estimates (National Maps) or County Level Estimates - State Maps homepage, select 'trends' to look at trends in county-level estimates. The legend categories have been set to the 2005 natural breaks categories to visualize the change in prevalence across years. For national maps, five natural breaks were used to view trends. For state maps, four natural breaks were used to view trends. Trends cannot be examined using either quartiles or ranks. For definitions of natural breaks and quartiles, see the glossary.

Top of Page

Can I map two categories at the same time?

Maps showing county-level estimates of the percentage of adults by the number of adults (i.e., bivariate maps) are available at the national level for the indicators (e.g., diagnosed diabetes). On the County-Level Estimates (National Maps) homepage, select "Percentage by the Number of Adults" from the Data Type drop-down box to view these national bivariate maps. At the state level, however, no bivariate maps are available at this time.

Top of Page

How do I interpret the different colors in the maps of county-level estimates?

Colors used in the shaded area maps represent the different levels of the scale. The lighter color represents the lowest level of the scale whereas the darker color represents the highest level of the scale.

Top of Page

How do I interpret the symbols in the maps of county-level estimates?

In the dot-density maps (i.e., maps showing the number of adults), the symbols used represent the different levels of the scale. The smallest dots represent the lowest level of the scale whereas the largest dots represent the highest level of the scale. In the bivariate maps (i.e., maps showing percentage by number of adults), small to large squares of different colors (blue, orange, red) were used to represent the gradation of the percentage of adults with diabetes by the total number of adults with diabetes. For example, for all indicators, the small blue squares indicate the lowest percentage of adults by the lowest total number of adults. On the other hand, the large red squares indicate the highest percentage of adults by the highest total number of adults.

Top of Page

Can I use the county maps and estimates to make comparisons or rank counties?

Caution should be exercised in making comparisons based on the county maps and estimates. The estimates are intended as individual point estimates. Significance testing or hypothesis testing may be inappropriate. The maps are presented for displaying possible geographic patterns and stimulating further investigation, but are not intended as formal representations of similarities and differences.

Bayesian 95% confidence intervals and standard deviations are provided as precision indicators of the individual county-level point estimates and should be used in data analyses.

One should not assume that counties mapped in different colors have significantly different prevalence. The county estimates are grouped in categories by various methods to produce a state or national map. This grouping does not incorporate the standard deviation or confidence interval and does not imply any formal comparison between counties.

Top of Page

How were ranks created for the data?

 

Ranks for county-level data of diagnosed diabetes and selected risk factors were based on age-adjusted prevalence rates. Models were fit using a Bayesian simulation method known as Markov Chain Monte Carlo.2-4 As part of the model fitting process we generated and saved two thousand draws from the distribution of each county's age-adjusted prevalence rate. For each of these draws we sorted the counties by prevalence and saved the counties' ranks. This gave us two thousand draws from the distribution of each county's rank. We then used the median for the rank estimate and the 5th and 95th percentiles for a 90% confidence interval. Note that ranks for Puerto Rico were not included with the national dataset because Puerto Rico ranks were not generated using the national data. Ranks for Puerto Rico are specific to that territory.

Top of Page

How can we use the county ranks?

 

A county's rank is a reflection of relative burden. The associated confidence interval quantifies the uncertainty associated with a county's rank and determines the extent to which conclusions may be based on ranks. For example, if a county's rank confidence interval is entirely below 1571, which is the median rank for all counties, we could confidently place that county in the lower half of counties.

Top of Page

How can we map the county ranks?

 

For each indicator (e.g., diagnosed diabetes), confidence intervals of counties' ranks were used to identify counties that were either below the median rank for all counties or above the median rank for all counties. On the County Level Estimates (National Maps) homepage, you can obtain the maps showing counties above and below the median rank by selecting "Low/High Median Rank" from the drop-down menu Data Type and then clicking GO. State-level maps are not available for ranks because the counties' ranks are based on the national estimates. For more information about mapping county ranks, see the related Morbidity and Mortality Weekly Report http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5845a2.htm.

Top of Page

Methodology for Mapping County-Level Estimates of Diagnosed Diabetes and Selected Risk Factors
 

What method was used to create the maps of county-level estimates?

The maps were created by merging the modeled estimates in database format, with geographic boundary files, called shapefiles. In this manner, the statistical data in the database were spatially referenced with their associated state and county boundaries. As a result, the data can be viewed as a map and the user can interactively map the geospatially-based data. The Albers Equal-Area (Continental United States) projection was used for the national maps and the NAD 1983 UTM Zone 14N map projection was used for the state maps.

Top of Page

What color sequences were used for the maps?

Color schemes were chosen based upon the number of data classes or categories, the types of data being mapped (e.g., number of adults versus percentage of adults), consideration of the display devices to be used for the resulting maps, and the need to avoid colors that cannot be differentiated by individuals with impaired color-vision.5 The color schemes for the maps were selected by referring to ColorBrewer (http://www.colorbrewer.org*), an online tool for selecting color schemes.

Top of Page

What method was used to produce the bivariate (i.e., percentage by number) maps of county-level estimates?

For all indicators, the data distribution for the number of adults and the percentage of adults was based on three classes or categories of natural breaks. The gradation of the percentage of adults by the total number of adults was mapped using small to large symbols of three different colors for a total of nine levels. See related information on interpreting symbols and colors in the maps. For the definition of natural breaks, see the glossary.

Top of Page

National and State Surveillance Data
 

What is the National Diabetes Statistics Report?

The National Diabetes Statistics Report is a report that summarizes the latest estimates of Americans with both diagnosed and undiagnosed diabetes. It is a collaborative effort involving CDC and the National Diabetes Education Program and other organizations in the U.S. Department of Health and Human Services, including the Agency for Health Research and Quality, the Centers for Medicare and Medicaid Services, the Food and Drug Administration, the Health Resources and Services Administration, the Indian Health Service, the National Institute of Diabetes and Digestive and Kidney Diseases, the National Diabetes Information Clearinghouse, and the Office of Minority Health. The American Diabetes Association, the American Association of Diabetes Educators, Juvenile Diabetes Research Foundation International, and U.S. Department of Veterans Affairs are also partners in the National Diabetes Statistics Report. The data in the statistics report will help national, state, and local health officials understand the health and economic burden of diabetes and better direct efforts to reach populations hardest hit by the disease.

Top of Page

Why is there a difference between the number of people with diagnosed diabetes in the National Diabetes Surveillance System and the National Diabetes Statistics Report?

The number of people with diagnosed diabetes in the National Diabetes Surveillance System http://www.cdc.gov/diabetes/statistics/prev/national/figpersons.htm and the National Diabetes Statistics Report http://apps.nccd.cdc.gov/ddtstrs/FactSheet.aspx are close but not exactly the same because the data sources, methodologies, and time periods are different. In the surveillance system, we use National Health Interview Survey (NHIS) data to estimate the U.S. population with diagnosed diabetes. In the statistics report, the estimate of the U.S. population with diagnosed diabetes comes from the National Health and Nutrition Examination Survey (NHANES) for those aged 20 years or older and the NHIS for those younger than 20 years. We use NHANES data in the statistics report because we present the number of people with diagnosed and undiagnosed diabetes; the medical examination component in NHANES allows us to estimate the number of people with undiagnosed diabetes. From NHIS, we can only obtain estimates of diagnosed diabetes.

If looking at trend data (i.e., looking at changes over time), refer to the National Diabetes Surveillance System. The data source, NHIS, and the methodology have been consistent throughout the years. If looking at a single year, refer to the National Diabetes Statistics Report. However, the statistics report should not be used for comparison across time because the methodology for estimating the U.S. population with diabetes has changed over time.

Top of Page

What is the difference between type 1 and type 2 diabetes?

Type 1 diabetes was previously called insulin-dependent diabetes mellitus (IDDM) or juvenile-onset diabetes. Type 1 diabetes develops when the body's immune system destroys pancreatic beta cells, the only cells in the body that make the hormone insulin that regulates blood glucose. To survive, people with type 1 diabetes must have insulin delivered by injection or a pump. This form of diabetes usually strikes children and young adults, although disease onset can occur at any age. Type 1 diabetes accounts for about 5% of all diagnosed cases of diabetes. Risk factors for type 1 diabetes may be autoimmune, genetic, or environmental. There is no known way to prevent type 1 diabetes. Several clinical trials of methods to prevent type 1 diabetes are currently in progress or are being planned.

Type 2 diabetes was previously called non-insulin-dependent diabetes mellitus (NIDDM) or adult-onset diabetes. Type 2 diabetes accounts for about 90% to 95% of all diagnosed cases of diabetes. It usually begins as insulin resistance, a disorder in which the cells do not use insulin properly. As the need for insulin rises, the pancreas gradually loses its ability to produce it. Type 2 diabetes is associated with older age, obesity, family history of diabetes, history of gestational diabetes, impaired glucose metabolism, physical inactivity, and race/ethnicity. African Americans, Hispanic/Latino Americans, American Indians, and some Asian Americans and Native Hawaiians or Other Pacific Islanders are at particularly high risk for type 2 diabetes and its complications. Type 2 diabetes in children below the age of 10 years is extremely rare. In youth aged 10–19 years it becomes more common, particularly in American Indians, African Americans, and Hispanic/Latino Americans.

Top of Page

Does the surveillance system provide estimates for type 1 and type 2 diabetes?

No questions are asked about the type of diabetes. We estimate the number and percentage of the U.S. population with diagnosed diabetes by using data from the National Health Interview Survey (NHIS) of the National Center for Health Statistics (NCHS), Centers for Disease Control and Prevention (CDC). All sampled adults are asked whether a health professional had ever told them they had diabetes. Also, parents of sampled children are asked whether their child had diabetes.

Top of Page

Can I make state-to-state comparisons?

Yes, the Diabetes Data and Trends Web site includes a feature where you can view state maps and tables and compare states across the same data category. However, you cannot compare county-level data within a state or across states due to the variability of the estimates.

Top of Page

Does the surveillance system include estimates of gestational diabetes?

No. We estimate the number and percent of the United States population with diagnosed diabetes by using data from the National Health Interview Survey (NHIS) of the National Center for Health Statistics (NCHS), Centers for Disease Control and Prevention (CDC). The number of women with gestational diabetes is excluded from the diabetes surveillance estimates. For estimates of gestational diabetes in the United States refer to the website Behavioral Risk Factor Surveillance System.

Top of Page

Does the surveillance system include prevalence estimates for American Indians/Alaska Natives?

No. The data sources used for diabetes surveillance do not provide an adequate sample size of this population to produce accurate and reliable estimates. However, several states, including Minnesota, Montana, New Mexico, North Carolina, and Oklahoma have conducted surveys with an oversample of American Indians. For the contact information of the state survey coordinators,
visit http://www2.cdc.gov/nccdphp/brfss2/coordinator.asp.

Top of Page

Why is there no national diabetes surveillance data for Hispanics prior to 1997?

The National Health Interview Survey, which is used to estimate diabetes prevalence in the United States, did not begin collecting data on Hispanics until 1997.

Top of Page

What is the difference between incidence and prevalence?

Incidence is the rate at which new events occur in a population. The numerator is the number of new events that occur in a defined period; the denominator is the population at risk of experiencing the event during this period.

Prevalence is the total number of all individuals who have an attribute or disease at a particular time (or during a particular period) divided by the population at risk of having the attribute or disease at this point in time (or midway through the period).

Top of Page

What is the difference between crude and age-adjusted rates?

The crude rate is the raw or unadjusted estimate.

The age-adjusted rate is an artificial estimate that minimizes the effects of different age distributions and allows comparisons between different populations. It represents what the crude rate would have been in the study population if that population had the same age distribution as a "standard" population. A "standard" population is a population in which the age composition is known precisely, for example, as a result of a census.

Top of Page

How many people with type 1 diabetes use insulin pumps?

Unfortunately, we do not have surveillance data on insulin pump use. However, surveillance data on insulin and oral medication use among adults with diagnosed diabetes, not specifically type 1 diabetes, are available at http://www.cdc.gov/diabetes/statistics/treating_national.htm.

Top of Page

Do you have surveillance data on reasons (e.g., lack of information about the need, inconvenience, cost, pain caused by the lancets) why people do not perform self-monitoring of blood glucose regularly?

We do not have surveillance data on barriers to self-monitoring of blood glucose.

Top of Page

References

  1. U.S. Census Bureau http://www.census.gov/popest/
  2. Rao JNK. Small Area Estimation. Ch.10:223:280. John Wiley & Sons; Hoboken, New Jersey, 2003.
  3. Malec D, Sedransk J, Moriarity CL, LeClere FB. Small Area Inference for Binary Variables in the National Health Interview Survey. Journal of the American Statistical Association 1997;92(439):815–826.
  4. Cadwell BL, Thompson TJ, Boyle JP, Barker LE. Bayesian Small Area Estimates of Diabetes Prevalence by U.S. County, 2005. Journal of Data Science 2010;8(1):173-188.
  5. Brewer, CA. Basic mapping principles for visualizing cancer data using geographic information systems (GIS). American Journal of Preventive Medicine 2006;30(2S):S25–S36.

Top of Page

 
* Links to non-Federal organizations found at this site are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization Web pages found at these links.
 

Know Your Score Widget. Flash Player 9 is required.
Know Your Score Widget.
Flash Player 9 is required.

CDC 24/7 – Saving Lives. Protecting People. Saving Money Through Prevention. Learn More About How CDC Works For You…
Contact Us:
  • Centers for Disease Control and Prevention
    1600 Clifton Rd
    Atlanta, GA 30333
  • 800-CDC-INFO
    (800-232-4636)
    TTY: (888) 232-6348
  • Contact CDC-INFO
USA.gov: The U.S. Government's Official Web PortalDepartment of Health and Human Services
Centers for Disease Control and Prevention   1600 Clifton Rd. Atlanta, GA 30329-4027, USA
800-CDC-INFO (800-232-4636) TTY: (888) 232-6348 - Contact CDC-INFO