Frequently
Asked Questions (FAQ) |
County Level Estimates
Maps
Data Sources and Methodology for County Level Estimates
of Diagnosed Diabetes
How to Read County-Level Estimates of Diagnosed Diabetes Maps
Methodology for Mapping County-Level Estimates of Diagnosed
Diabetes
National and State Surveillance Data
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County Level Estimates Maps |
Data Sources and Methodology
for County-Level Estimates of Diagnosed Diabetes |
What
method is used to create 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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Can
I download the county-level estimates of diagnosed diabetes map data? |
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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Where
are the definitions for variables that are found in the downloadable county-level estimates of diagnosed diabetes data? |
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 |
How
do I access the various types of maps available? |
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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What
factors do I need to choose to display a map? |
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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Can
I map two categories at the same time? |
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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How
do I interpret the different colors in the county-level estimates of
diagnosed diabetes map? |
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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How
do I interpret the symbols in the county-level
estimates of diagnosed
diabetes map? |
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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Can I use the county maps and estimates to make comparisons, rank counties,
or evaluate trends? |
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 |
What
method is used to create the county-level
estimates of diagnosed diabetes
maps? |
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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What
color sequences were used for the maps? |
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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What
method was used to produce the bivariate county-level estimates of diagnosed
diabetes map? |
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 |
What
is the National Diabetes Fact Sheet? |
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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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 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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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.
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Can
I make state-to-state comparisons? |
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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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.
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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.
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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.
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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).
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Do
you have surveillance data for
the reasons why people do not perform
regular self-monitoring fail to do so (i.e., lack of information about
the need, inconvenience, cost, pain caused by the lancets, etc.)? |
We do not have surveillance data on
barriers to self-monitoring of blood glucose.
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References |
- U.S. Census Bureau http://www.census.gov/popest/estimates.php
- Rao JNK. Small Area Estimation. Ch.10:223:280. John Wiley &
Sons; Hoboken, New Jersey, 2003.
- 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.
- 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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