Frequently Asked Questions (FAQ)

County Level Estimates Maps

Data Sources and Methodology for County Level Estimates of Diagnosed Diabetes

• References
• What method is used to create county-level estimates of diagnosed diabetes?
• Can I download the county-level estimates of diagnosed diabetes map data?
• Where are the definitions for variables that are found in the downloadable county-level estimates of diagnosed diabetes data?

How to Read County-Level Estimates of Diagnosed Diabetes Maps

• How do I access the various types of maps available?
• What factors do I need to choose to display a map?
• Can I map two categories at the same time?
• How do I interpret the different colors in the county-level estimates of diagnosed diabetes map?
• How do I interpret the symbols in the county-level estimates of diagnosed diabetes map?
• Can I use the county maps and estimates to make comparisons, rank counties, or evaluate trends?

Methodology for Mapping County-Level Estimates of Diagnosed Diabetes

• What method is used to create the county-level estimates of diagnosed diabetes maps?
• What color sequences were used?
• What method was used to produce the bivariate county-level estimates of diagnosed diabetes map?

National and State Surveillance Data

• What is the National Diabetes Fact Sheet?
• What is the difference between type 1 and type 2 diabetes?
• Does the surveillance system provide estimates for type 1 and type 2 diabetes?
• Can I make state-to-state comparisons?
• Does the surveillance system include estimates of gestational diabetes?
• Does the surveillance system include prevalence estimates for American Indians/Alaska Natives?
• Why is there no national diabetes surveillance data for Hispanics prior to 1997?
• What is the difference between incidence and prevalence?
• What is the difference between crude and age-adjusted rates?
• Do you have surveillance data for the reasons why people do not perform regular self-monitoring? (i.e., lack of information about the need, inconvenience, cost, pain caused by the lancets, etc.)?

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County Level Estimates Maps

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

The prevalence of diagnosed diabetes 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. Three years of data are used to improve the precision of the year-specific county-level estimates of diagnosed diabetes estimates. For example, 2003, 2004, and 2005 are used for the 2004 estimate and 2004, 2005, and 2006 are used for the 2005 estimate. Estimates are 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 3,141 counties or county equivalents (e.g., parish, borough) in the 50 U.S., states and the District of Columbia are based on indirect model-dependent estimates.² 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 are used to obtain estimates. Separate models are 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 is included as a county-level covariate. The model specification is essentially the same as Malec, et al.³

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Excel and HTML files with county estimates for the entire nation and for each state are available for downloading. National data is available as a link located below the national maps, and the state data is available as a link below each state map.

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The national-level and state-level variables with definitions are located in Data Dictionary, shown as a link beside each downloadable file. Variables found in the national and state data sets are the same except for variables PERTOT04, and PERTOT05, which are found in the national data set used to produce the national bivariate maps.

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How to Read County-Level Estimates of Diagnosed Diabetes Maps

National-level and state-level views are available for county estimates of diagnosed diabetes. You can obtain county estimates within a state through the Data and Trends homepage or the County-Level Estimates homepage. On the County-Level Estimates homepage, you must select your state of interest from the drop-down menu,View Estimates by State and then click GO. On the Data and Trends homepage, select your state of interest from the drop-down menu under State Surveillance Data including County Maps and then click GO, or click directly on the state on the map.

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For county-level estimates of diagnosed diabetes maps, select a State, Year (2004, 2005), Classification (natural breaks, quartiles), and Data Type (% with diabetes, number with diabetes) and then click GO. For national maps of county estimates, select a Year, Data Type, and Classification and then click GO.

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Within a state, county-level estimates are available for the percentage of adults with diagnosed diabetes and the number of adults with diagnosed diabetes, but no bivariate maps (e.g., prevalence by number) are available. However, a bivariate map of percentage of adults with diabetes by number of adults with diabetes is available at the national level. To view this map under County-Level Estimate, select “Both” from the Data Type drop-down box.

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Colors used in the shaded area maps represent the different levels of the scale. The lighter color (e.g., light yellow) represents the lowest level of the scale whereas the darker color (e.g., red or dark brown) represents the highest level of the scale.

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Symbols used in the dot-density maps 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. Small to large squares of different colors (blue, orange, red) were used in bivariate maps to represent the gradation of percentage of adults with diabetes by total number of adults with diabetes. For example, the lowest percentage of adults with diabetes by the lowest total number of adults with diabetes is denoted by small blue squares. The highest percentage of adults with diabetes by the highest total number of adults with diabetes is denoted by large red squares.

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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-point estimates, and should be used in data analyses.

Ranks have not been estimated and ranking the data is not recommended.

One should not assume that counties mapped in different colors have significantly different diabetes prevalence. To produce a state or national map, the county estimates are grouped in categories (natural breaks or quartiles). This grouping does not incorporate the standard deviation or confidence interval, and does not imply any formal comparison between counties.

Trends should also be evaluated with caution. Direct comparison of the 2004 national and state maps to the 2005 maps is not possible. The quantiles and natural breaks were estimated separately for each year, and the categories used for the maps are not the same.

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Methodology for Mapping County-Level Estimates of Diagnosed Diabetes

The maps are created by merging the modeled estimates in database format, with geographic boundary files, called shapefiles. In this manner, the statistical data in the database are 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. Users can specify the use of natural breaks or quartiles to classify the data. The NAD 1983 UTM Zone 14N map projection was used for state maps. The Albers Equal-Area (Continental United States) projection was used for national maps.

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Color schemes were chosen based upon the number of data classes, the types of data being mapped (e.g., number of adults versus percent 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.⁴ The color schemes for the maps were selected by referring to ColorBrewer (http://www.colorbrewer.org*), an online tool for selecting color schemes.

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The data distribution for percentage of adults with diabetes was based on three classes of natural breaks. The data distribution for the number of adults with diabetes was based on three classes of natural breaks. The gradation of percentage of adults with diabetes by total number of adults with diabetes was mapped using small to large symbols of three different colors for a total of nine levels. The variable is defined in Data Dictionary.

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National and State Surveillance Data

The National Diabetes Fact Sheet 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 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 Fact Sheet. The data in the fact sheet 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.

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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 5% to 10% 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.

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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.

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Yes, the Data and Trends Web site includes a feature where you can view maps and tables and compare states across data categories.

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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.

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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.

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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.

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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).

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

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1. U.S. Census Bureau http://www.census.gov/popest/estimates.php
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. Brewer, CA. Basic mapping principles for visualizing cancer data using geographic information systems (GIS). American Journal of Preventive Medicine 2006;30(2S):S25–S36.

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