How is the new case definition of doctor-diagnosed
(used since 2002) different from the old case definition (used 1996–2001)?
From 1996 to 2001, the case definition included those with
doctor-diagnosed arthritis and/or
those with chronic joint symptoms and labeled them “arthritis or chronic joint
symptoms.”
Since 2002, CDC, partners, and outside experts have agreed on a new
case definition of simply “doctor-diagnosed arthritis.”
[Note: People with chronic joint symptoms but no doctor-diagnosed arthritis, are now
called “possible arthritis.” Estimates for “possible arthritis”
should not be added to estimates for doctor-diagnosed arthritis.
See more about “possible arthritis.”]
Back to top
Why was the arthritis case definition changed in
2002?
CDC, partners, and outside experts agreed to use a new definition, starting
in 2002. The reasons for this were many.
First, the questions used to determine both doctor-diagnosed arthritis and
chronic joint symptoms were changed. A summary of the BRFSS arthritis questions from
1996 on can be found in the following document.
Because of the change in the questions and the results of validation studies, a new case definition appeared in order. Using doctor-diagnosed arthritis as
the definition:
Back to top
What estimate best indicates the prevalence of
arthritis for the nation?
National estimates should come from a national survey; CDC uses the National Health Interview Survey (NHIS) for such estimates.
Healthy People 2010 also recommends using NHIS data for national estimates.
Using NHIS data (2003-2005), we estimate that 46.4 million (21.6%)
adults had doctor-diagnosed arthritis.
Back to top
There are differences in the national arthritis
prevalence estimates between 2001 to 2002. Why?
There are three main reasons account for the differences.
Back to top
Why did CDC add the four types of
arthritis to the end of the survey question addressing doctor-diagnosed
arthritis: “Have you ever been told by a doctor or other health professional
you have some form of arthritis, rheumatoid arthritis, gout, lupus, or fibromyalgia?”
For public health surveillance, we are trying to capture more than 100 diseases
that are considered “arthritis or other rheumatic conditions.” Some of these
conditions may not be readily recognized as arthritis by survey respondents. Experts recommended adding these conditions.
Back to top
Why are the neck and back excluded from the survey
question addressing joint symptoms: “The next questions refer to your joints.
Please do NOT include the back or neck. DURING THE PAST 30 DAYS, have
you had any symptoms of pain, aching, or stiffness in or around a joint?”
Although many types of arthritis can affect the neck and back,
many neck and back symptoms are due to
other conditions. Experts recommended we exclude those with neck or back
symptoms to assure a conservative estimate of doctor-diagnosed arthritis.
Back to top
Should people with
doctor-diagnosed arthritis but no chronic joint symptoms be excluded from the
prevalence estimate?
No, they should not be excluded from prevalence estimates.
It is not unusual for joint symptoms to come
and go as the condition worsens and improves. Moreover, the use of medications
can affect the occurrence of joint symptoms. Accordingly, we would not
exclude these persons when making estimates of the prevalence of arthritis.
State prevalence estimates should be for all persons with doctor-diagnosed
arthritis regardless of whether they have symptoms at the time they are surveyed.
Back to top
Is self-reported information on the type of arthritis
valid?
The CDC
Arthritis Program strongly discourages the collection and reporting of
self-reported data on arthritis type (e.g., osteoarthritis, rheumatoid
arthritis, lupus) because self-reported condition data have been shown to be
inaccurate based on studies done
by the program and other researchers. For example, the CDC Arthritis Program
compared how frequently the arthritis condition type reported by participants in
the Medical Expenditure Panel Survey1 (MEPS) agreed with each of
the participants’ doctor’s diagnosis. This study found that among persons
whose doctor had diagnosed them with osteoarthritis, only 9% of survey
participants reported that they had osteoarthritis. Since self-reported
information on type of arthritis is not valid, the CDC arthritis program
discourages states and researchers from measuring and using data on
self-reported arthritis condition type.
1 The Medical Expenditure Panel Survey is a nationally
representative survey of the U.S. civilian non-institutionalized population.
Back to top
What is CDC doing to learn more about the people with
possible arthritis?
Analyses are under way to further
characterize this group. Four states
collected additional information through the 2005 BRFSS on this specific
population. Two of the questions are: 1) “Earlier you said you had never seen
a doctor about your joint symptoms. Please tell me why you did not see a
doctor about your joint symptoms?” 2) “Earlier you said you had seen a doctor
for your joint symptoms. What did the doctor say was the cause of your joint
symptoms?” The responses to these questions should give us additional insight
about this group. We will share results of this work as it
becomes available. Additionally, CDC will be analyzing data for people with
possible arthritis from a national sample collected in 2005-2006 through the
Arthritis Conditions Health Effects Survey (ACHES).
See note.
Back to top
What changes are expected for future BRFSS surveys?
We expect BRFSS will continue to put arthritis questions on the core in odd
numbered years, although the number of questions allotted for arthritis may
decrease in future years. We are proposing a new arthritis questions for the
BRFSS Core in 2009. A list of BRFSS
Arthritis Core (Burden Questions) by year is available.
Back to top
How often are the Arthritis Burden Questions on
the BRFSS survey?
Starting in 2003, the BRFSS Arthritis Core
(Burden Questions) are offered on the core survey in odd
numbered years. State programs are encouraged to add the optional module
known as the
BRFSS Arthritis Optional Module (Management
Questions) in the same odd-numbered year. Although states may be
interested in using the questions every year, CDC will NOT financially or
analytically support the use of any arthritis questions in even numbered
years. States may add them as state-added questions.
Back to top
What does the CDC
Arthritis Program recommend state arthritis programs do regarding the BRFSS
survey in even years?
CDC is not supporting the use of arthritis questions in even years. This means
we are not funding the BRFSS to put the questions on the survey nor are we
providing our standard analytic tables, as we
do for all states using odd number year data. Any use of
these questions in even years would have to be as state-added questions. We do
not feel it is necessary to have the data each year, as the prevalence is
unlikely to change rapidly and with lots of programs competing for space on the
questionnaire, one can quickly wear their welcome out with the BRFSS
coordinator. In infrequent instances, when a state feels it is imperative for
its program to make substate prevalence estimates (e.g., for large cities),
it may choose to use the arthritis questions in even years. CDC is unable to
provide any support for doing this and we don’t recommend it.
Back to top
Is there more than
one way to define a “case” of arthritis?
Yes, the purpose (e.g., estimating prevalence or assessing
burden) and source of the data
determine the arthritis case definition to be used. In general, data used in arthritis
surveillance falls into two broad categories, self-reported data and health
care system data.
For the purpose of estimating the population prevalence of arthritis, we
recommend using self-reported data as the data source and using doctor-diagnosed
arthritis as the case definition. Both the state-based Behavioral Risk
Factor Surveillance System (BRFSS) and National Health Interview Survey (NHIS)
are self-reported data surveys, and use doctor-diagnosed arthritis as the case
definition. A “case” of doctor-diagnosed arthritis in these surveys is defined
as a “yes” answer to the following question: “Have you EVER been told by a
doctor or other health professional that you have some form of arthritis,
rheumatoid arthritis, gout, lupus, or fibromyalgia?” Further information on the
CDC arthritis case definition
is available.
For assessing the burden of arthritis using
health care system data (e.g.
hospital discharge data, ambulatory care, death.)
a “case” of arthritis is defined by the
National Arthritis Data Workgroup definition using
arthritis related ICD–9–CM codes
(PDF-73K) and
is labeled “arthritis and other rheumatic conditions”. The CDC discourages
states from pursuing these assessments unless there is a direct link to program
activity that is consistent with the state arthritis plan.
Be aware that other studies (e.g., clinical trials) including some statistics
and studies cited elsewhere on this Website, have different data sources and use
different arthritis case definitions.
Back to top