Case Definition FAQs

This case-finding question appears in two US-based surveys.

• It has appeared in the US-based National Health Interview Survey (NHIS) since 2002. The question is asked annually.
• It has appeared in the state-based Behavioral Risk Factor Surveillance System (BRFSS) since 2003. From 2003 to 2009, this question was asked in alternating years, and it has been asked annually from 2010 to the present.

The survey question lists four specific types of arthritis: rheumatoid arthritis, gout, lupus, and fibromyalgia. The question lists these specific conditions because survey respondents may not readily recognize some of these conditions as arthritis. For public health surveillance, CDC aims to identify people with one of at least 100 diseases that are considered “arthritis or other rheumatic conditions.”  The National Arthritis Data Workgroup expert panel recommended that the definition include these four conditions.

Reference:

Helmick CG, Lawrence RC, Pollard RA, Lloyd E, Heyse SP. Arthritis and other rheumatic conditions: who is affected now, who will be affected later? National Arthritis Data Workgroup. Arthritis Care Res. 1995;8(4):203–211. PubMed PMID: 8605258 html

Multiple studies show that people who have osteoarthritis may not remember the specific diagnosis of osteoarthritis or may confuse their diagnosis of osteoarthritis with rheumatoid arthritis.  For example, one study using data from the Medical Expenditure Panel Survey (MEPS) found that only 35% of respondents who had a health care provider diagnosis of osteoarthritis reported that they had osteoarthritis. Many respondents simply reported that they had arthritis. We believe that most people with osteoarthritis are captured by the term “arthritis” in the question.

Reference:

Cisternas MG, Murphy L, Sacks JJ, Solomon DH, Pasta DJ, Helmick CG. Alternative methods for defining osteoarthritis and the impact on estimating prevalence in a US population-based survey. Arthritis Care Res (Hoboken). 2016;68(5):574–580. doi: 10.1002/acr.22721. PubMed PMID: 26315529; PubMed Central PMCID: PMC4769961. Abstract

CDC includes fibromyalgia for three reasons.

1. The case definition for arthritis and other rheumatic conditions includes fibromyalgia because the doctors who treat arthritis, rheumatologists, also treat fibromyalgia. Additionally, the National Arthritis Data Workgroup expert panel recommended including it in this definition.
2. Many of the symptoms of fibromyalgia, such as joint pain and stiffness, fatigue, and depression, resemble those of arthritis. For this reason, arthritis surveillance is the most appropriate fit for fibromyalgia across the various conditions monitored by public health surveillance in the United States.
3. The public health interventions that are effective for managing arthritis are also effective for managing fibromyalgia. To help people with fibromyalgia reduce their symptoms and improve function and quality of life, CDC recommends proven self-management strategies. These strategies include getting regular physical activity, participating in community-based self-management education programs, and maintaining a healthy weight.

Learn more about CDC-recommended arthritis self-management strategies on our Five Key Public Health Messages page.

Osteoporosis is not included in the arthritis definition because it is a metabolic bone disease and not arthritis or a rheumatic condition.
Some neck/back problems are caused by arthritis, but most are not. If they were included in the arthritis definition, the definition would contain too many conditions that are not arthritis or a rheumatic condition. By not including these cases, we are undercounting arthritis slightly which is preferable to substantial overcounting.

National estimates should come from a survey designed to represent a national population. CDC uses the National Health Interview Survey (NHIS) for such estimates. Healthy People 2020 also recommends using NHIS data for national estimates.

See our National Statistics page for current national prevalence estimates.

Reference:

Barbour KE, Helmick CG, Boring M, Brady TJ. Vital signs: prevalence of doctor-diagnosed arthritis and arthritis-attributable activity limitation—United States, 2013–2015. Morb Mortal Wkly Rep. 2017;66:246–253. DOI: 10.15585/mmwr.mm6609e1 html

CDC recommends calculating state-specific estimates from the Behavioral Risk Factor Surveillance System (BRFSS). The BRFSS provides estimates for the 50 US states, the District of Columbia, and three US territories (Guam, Puerto Rico and US Virgin Islands).

• For current state arthritis prevalence, see our State Statistics page.
• For state-specific prevalence by county and for selected characteristics by state, see the MMWR Surveillance Summary: “Geographic Variations in Arthritis Prevalence, Health-Related Characteristics, and Management—United States, 2015.”

Reference:

Barbour KE, Moss S, Croft JB, et al. Geographic variations in arthritis prevalence, health-related characteristics, and management—United States, 2015. MMWR Surveill Summ. 2018;67(No. SS-4):1–28. doi: 10.15585/mmwr.ss6704a1. html

The CDC Arthritis Program (the Program) strongly discourages the collection and reporting of self-reported data on specific types of arthritis (e.g., osteoarthritis, rheumatoid arthritis, and lupus). Scientific studies demonstrate that self-reported condition information for specific types of arthritis is inaccurate. For example, as described above for osteoarthritis, many individuals who have osteoarthritis do not report it. Many people who self-report rheumatoid arthritis do not have it. Because self-reported information on type of arthritis is not valid, the Program discourages states and researchers from measuring and using self-reported data for specific types of arthritis. Instead, we recommend using data that incorporate clinical information, such as ambulatory or hospital care records.

In 2011, BRFSS made two major changes to the survey.

1. BRFSS moved the case finding question for doctor-diagnosed arthritis from the Arthritis Burden module and into a new Chronic Health Conditions core section. This section includes questions for other chronic conditions.
   • The three other questions remain in the Arthritis Burden core section.
   • The change in the sequence of questions may alter respondents’ answers to the arthritis-related questions.
2. BRFSS made substantial changes to its methods including the survey sampling and weighting procedures. Therefore, estimates of doctor-diagnosed arthritis calculated from BRFSS in 2011 and subsequent BRFSS surveys are not comparable with estimates of doctor-diagnosed arthritis calculated from BRFSS surveys prior to 2011.

When studying time trends, CDC strongly recommends analyzing data for 1996–2001, 2003–2009 or 2011 forward but not combining data across these periods (for example, 1996–2009).  The reason data should not be combined across time periods is that it is then impossible to know if any change in prevalence across these periods is real or actually due to the changes to the BRFSS survey.

BRFSS analysts should not combine 1996–2001 BRFSS data with subsequent years because in 2003, the arthritis case definition on BRFSS changed to its current form; BRFSS did not collect information on arthritis in 2002.