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Estimates of Pain Prevalence and Severity in Adults: United States, 2012

  • Richard L. Nahin
    Correspondence
    Address reprint requests to Richard L. Nahin, PhD, MPH, National Center for Complementary and Integrative Health, National Institutes of Health, 6707 Democracy Blvd., Suite 401, Bethesda, MD 20892-5475.
    Affiliations
    National Center for Complementary and Integrative Health, National Institutes of Health, Bethesda, Maryland
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      Highlights

      • 2012 estimates of pain prevalence and severity are presented for U.S. adults.
      • A simple, 2-item measure for categorizing pain severity is introduced.
      • Pain persistence and bothersomeness designate 5 discrete categories of pain severity.
      • The study describes the concurrent validation of the measure.
      • Pain severity is associated with race, ethnicity, preferred language, sex, and age.

      Abstract

      Using a simple approach for coding pain severity, the present study describes self-reported pain in U.S. adults. Data are included for 8,781 adults who completed the Functioning and Disability Supplement of the 2012 National Health Interview Survey. An internationally piloted pain severity coding system was used to group participants into 5 discrete ordered pain categories based on their pain persistence (days with pain in the last 3 months) and bothersomeness (little, a lot, somewhere in between): pain free and categories 1 (low) to 4 (high). It is estimated that 126.1 million adults reported some pain in the previous 3 months, with 25.3 million adults (11.2%) suffering from daily (chronic) pain and 23.4 million (10.3%) reporting a lot of pain. Based on the persistence and bothersomeness of their pain, 14.4 million adults (6.4%) were classified as having the highest level of pain, category 4, with an additional 25.4 million adults (11.3%) experiencing category 3 pain. Individuals with category 3 or 4 pain were likely to have worse health status, to use more health care, and to suffer from more disability than those with less severe pain. Associations were seen between pain severity and selected demographic variables including race, ethnicity, preferred language, sex, and age.

      Perspective

      U.S. estimates of pain prevalence are presented using a simple approach for assigning pain severity developed by the Washington Group on Disability Statistics. Concurrent validity is assessed. Although this approach is promising, additional work is required to determine the usefulness of the Washington Group pain categories for pain research or clinical practice.

      Key words

      “Pain is always subjective.”
      International Association for the Study of Pain, Task Force on Taxonomy
      Pain terms, a current list with definitions and notes on usage.
      Because there are no objective measures of pain, patient reports are necessarily the primary source of estimates of pain prevalence and severity. Nevertheless, as stated by the Institute of Medicine (IOM),
      Institute of Medicine
      Relieving Pain in American: A Blueprint for Transforming Prevention, Care, Education and Research.
      “obtaining a definitive picture of the extent and significance of pain is difficult. Current data on the incidence, prevalence and consequences of pain are not consistent or complete, in part because in many cases pain is treated as a symptom and what is collected is data on underlying conditions or events.” The IOM further states: “data weaknesses previously discussed are particularly important when one is examining racial and ethnic disparities.”
      Institute of Medicine
      Relieving Pain in American: A Blueprint for Transforming Prevention, Care, Education and Research.
      Most available survey data on the prevalence of pain in demographic groups in the U.S. population have focused on the prevalence of chronic or persistent pain (eg, see
      • Hardt J.
      • Jacobsen C.
      • Goldberg J.
      • Nickel R.
      • Buchwald D.
      Prevalence of chronic pain in a representative sample in the United States.
      • Johannes C.B.
      • Le T.K.
      • Zhou X.
      • Johnston J.A.
      • Dworkin R.H.
      The prevalence of chronic pain in United States adults: Results of an Internet-based survey.
      • Kennedy J.
      • Roll J.M.
      • Schraudner T.
      • Murphy S.
      • McPherson S.
      Prevalence of persistent pain in the U.S. adult population: New data from the 2010 National Health Interview Survey.
      ) or health conditions associated with pain (eg, see
      • Bolen J.
      • Schieb L.
      • Hootman J.M.
      • Helmick C.G.
      • Theis K.
      • Murphy L.B.
      • Langmaid G.
      Differences in the prevalence and severity of arthritis among racial/ethnic groups in the United States, National Health Interview Survey, 2002, 2003, and 2006.
      • Deyo R.A.
      • Mirza S.K.
      • Martin B.I.
      Back pain prevalence and visit rates: Estimates from U.S. national surveys, 2002.
      • Plesh O.
      • Adams S.H.
      • Gansky S.A.
      Racial/ethnic and gender prevalences in reported common pains in a national sample.
      • Strine T.W.
      • Hootman J.M.
      US national prevalence and correlates of low back and neck pain among adults.
      ). These studies found almost uniformly that whites have higher prevalence rates of chronic pain and painful conditions than minority groups. The picture from surveys that compare pain frequency or intensity across racial/ethnic groups is not so clear: whereas some studies report more pain or greater pain severity in minorities,
      • Grubert E.
      • Baker T.A.
      • McGeever K.
      • Shaw B.A.
      The role of pain in understanding racial/ethnic differences in the frequency of physical activity among older adults.
      • Hitt H.C.
      • McMillen R.C.
      • Thornton-Neaves T.
      • Koch K.
      • Cosby A.G.
      Comorbidity of obesity and pain in a general population: Results from the Southern Pain Prevalence Study.
      • Meghani S.H.
      • Cho E.
      Self-reported pain and utilization of pain treatment between minorities and nonminorities in the United States.
      • Nguyen M.
      • Ugarte C.
      • Fuller I.
      • Haas G.
      • Portenoy R.K.
      Access to care for chronic pain: Racial and ethnic differences.
      others report less pain
      • Chowdhury P.P.
      • Balluz L.
      • Strine T.W.
      Health-related quality of life among minority populations in the United States, BRFSS 2001-2002.
      • Johannes C.B.
      • Le T.K.
      • Zhou X.
      • Johnston J.A.
      • Dworkin R.H.
      The prevalence of chronic pain in United States adults: Results of an Internet-based survey.
      or no difference.
      • Portenoy R.K.
      • Ugarte C.
      • Fuller I.
      • Haas G.
      Population-based survey of pain in the United States: Differences among white, African American, and Hispanic subjects.
      • Reyes-Gibby C.C.
      • Aday L.A.
      • Todd K.H.
      • Cleeland C.S.
      • Anderson K.O.
      Pain in aging community-dwelling adults in the United States: Non-Hispanic whites, non-Hispanic blacks, and Hispanics.
      These surveys differed in the population sampled, the definition of pain, the methods to measure pain frequency and severity, and how minorities groups are combined for the analyses. There are few data on Asians and other nonblack, non-Hispanic minority groups in these analyses. Also absent from this literature are age-specific and sex-specific prevalence rates of pain frequency and severity in minority groups.
      Data from the 2012 National Health Interview Survey (NHIS) provide a unique opportunity to develop a broader picture of pain within the U.S. adult population. The 2012 NHIS asked participants about the persistence (frequency) and bothersomeness (intensity) of pain experienced in the previous 3 months. Questions included in the 2012 NHIS allow a graded assessment of pain severity, using methods developed and validated qualitatively and with mixed-method assessment by the Washington Group on Disability Statistics.
      • Madans J.H.
      • Loeb M.E.
      • Altman B.M.
      Measuring disability and monitoring the UN Convention on the Rights of Persons with Disabilities: The work of the Washington Group on Disability Statistics.
      • Madans J.H.
      • Loeb M.
      Methods to improve international comparability of census and survey measures of disability.
      • Miller K.
      • Loeb M.
      Mixed-Method Assessment of Validity and Cross-Subgroup Comparability. AAPOR 69th Annual Conference.

      Washington Group on Disability Statistics. Available at: http://www.cdc.gov/nchs/washington_group.htm. Accessed April 23, 2015

      Also available in NHIS is information on an extended list of potentially painful health conditions. The complex sampling design of the NHIS allows some confidence in extrapolations to the U.S. adult population, and the survey is of sufficient size to examine differences among subpopulations.
      The purpose of this article is twofold. First, we present data on the concurrent validity of the Washington Group categories of pain severity. We then use these pain categories to investigate whether there is significant heterogeneity in pain status between whites and minority groups. The data presented here begin to answer the IOM's
      Institute of Medicine
      Relieving Pain in American: A Blueprint for Transforming Prevention, Care, Education and Research.
      call for national data “to describe the nature and extent of the [pain] problem” and “to identify subpopulations that will benefit more from future interventions.”

      Methods

      Population

      The data used in this report are from the 2012 NHIS Sample Adult Core and the NHIS Adult Functioning and Disability Supplement (AFD).
      National Center for Health Statistics
      Data File Documentation, National Health Interview Survey, 2012.
      The NHIS is an annual survey of the health of the U.S. civilian, noninstitutionalized population conducted by the National Center for Health Statistics, Centers for Disease Control and Prevention. This in-person survey contains 4 main modules: household, family, sample child, and sample adult. The first 2 modules collect health and sociodemographic information on each member of all families residing within a sampled household. Within each family, additional information is collected from 1 randomly selected adult (the sample adult) aged 18 years or older. Bilingual interviewers or interpreters were recruited to interview all respondents who preferred using a language other than English. A Spanish language version is available for participants who prefer speaking in Spanish. The survey uses a multistage clustered sample design and oversamples black, Asian, and Hispanic populations. When combined with sampling weights derived from the Centers for Disease Control and Prevention, this design allows accurate extrapolation of findings to the civilian, noninstitutionalized U.S. adult population.
      For the 2012 interview sample, there were 42,366 households, consisting of 108,131 persons in 43,345 families. The total household response rate was 77.6%. From the households interviewed, 34,525 adults completed interviews, resulting in an overall sample adult response rate of 79.7%. Approximately one-quarter of sampled adults were randomly chosen to participate in the AFD supplement. Almost all chosen adults (8,781) completed the supplement, resulting in a 98% supplement response rate.
      The 2012 NHIS was approved by the National Center for Health Statistics Research Ethics Review Board. Verbal consent was obtained from all survey respondents.

      Dependent Variable: Assessment of Pain

      The AFD collected information on the persistence and bothersomeness of self-reported pain in the previous 3 months. The Washington Group on Disability Statistics, constituted by the United Nations Statistical Commission, developed and validated these questions through cognitive testing and pilot surveys in the United States and internationally.
      • Madans J.H.
      • Loeb M.E.
      • Altman B.M.
      Measuring disability and monitoring the UN Convention on the Rights of Persons with Disabilities: The work of the Washington Group on Disability Statistics.
      • Madans J.H.
      • Loeb M.
      Methods to improve international comparability of census and survey measures of disability.
      • Miller K.
      • Loeb M.
      Mixed-Method Assessment of Validity and Cross-Subgroup Comparability. AAPOR 69th Annual Conference.

      Washington Group on Disability Statistics. Available at: http://www.cdc.gov/nchs/washington_group.htm. Accessed April 23, 2015

      Respondents were first asked how often they had pain in the previous 3 months: never, some days, most days, or every day. Data from this question provide estimates of the 3-month persistence (period prevalence) of pain. For those who had pain on at least some days, a follow-up question assessing bothersomeness was asked: “Thinking about the last time you had pain, how much pain did you have—a little, between a little and a lot, or a lot.” Ninety-six percent of AFD participants completed these pain questions. Given this high response rate, no attempt was made to impute missing data. To compare the present data with the literature on the prevalence of chronic pain (defined here as pain for at least half the days in a 6-month period
      • Deyo R.A.
      • Dworkin S.F.
      • Amtmann D.
      • Andersson G.
      • Borenstein D.
      • Carragee E.
      • Carrino J.
      • Chou R.
      • Cook K.
      • DeLitto A.
      • Goertz C.
      • Khalsa P.
      • Loeser J.
      • Mackey S.
      • Panagis J.
      • Rainville J.
      • Tosteson T.
      • Turk D.
      • Von Korff M.
      • Weiner D.K.
      Report of the NIH Task Force on research standards for chronic low back pain.
      National Pain Strategy Task Force
      Draft National Pain Strategy.
      ), individuals who reported having pain every day in the previous 3 months were coded as having chronic pain.
      For individuals reporting pain at least some days, the Washington Group
      • Miller K.
      • Loeb M.
      Mixed-Method Assessment of Validity and Cross-Subgroup Comparability. AAPOR 69th Annual Conference.
      has suggested a coding scheme that combines persistence and bothersomeness of pain to create 4 discrete categories of increasingly severe pain (Table 1). This coding scheme was tested and validated in a number of countries using a variety of qualitative and mixed-method assessments such as cognitive testing.
      • Madans J.H.
      • Loeb M.E.
      • Altman B.M.
      Measuring disability and monitoring the UN Convention on the Rights of Persons with Disabilities: The work of the Washington Group on Disability Statistics.
      • Madans J.H.
      • Loeb M.
      Methods to improve international comparability of census and survey measures of disability.
      • Miller K.
      • Loeb M.
      Mixed-Method Assessment of Validity and Cross-Subgroup Comparability. AAPOR 69th Annual Conference.

      Washington Group on Disability Statistics. Available at: http://www.cdc.gov/nchs/washington_group.htm. Accessed April 23, 2015

      Table 1Pain Severity Categories Based on Pain Persistence and Bothersomeness
      CategoryPain Persistence (Last 3 Months)Pain Bothersomeness (Last Time You Had Pain)
      Pain freeNo pain in last 3 monthsNot applicable
      Category 1 pain
       DefinitionSome daysA little pain
      Category 2 pain
       Definition 1Most or every dayA little pain
       or
       Definition 2Some daysBetween a little and a lot
      Category 3 pain
       Definition 1Some daysA lot
       or
       Definition 2Most or every dayBetween a little and a lot
      Category 4 pain
       DefinitionMost or every dayA lot of pain

      Demographic Variables

      Language of Interview, Ethnicity, and Race

      Based on self-identified race and ethnicity and on the language of interview as reported by the interviewers, individuals were coded into 16 discrete categories. Data for the following 7 groups are presented in Table 2: 1) non-Hispanic whites (NHW) who preferred English (reference group); 2) non-Hispanic blacks (NHB) who preferred English; 3) non-Hispanic Asians (NHA) who preferred English; 4) non-Hispanic individuals who did not self-report as white, black, or Asian (“other races” includes those self-reporting as of mixed race) who preferred English; 5) Hispanic whites (HW) who preferred English, 6) NHA who did not prefer English; and 7) HW who did not prefer English (HWNE). Because of small sample sizes and resulting large variance (greater than 25% of the point estimate), data for other race/ethnic/language groups are not presented in the tables but were included in the regression models. No Hispanic Asians (any language) were identified in the sample.
      Table 2Demographic Characteristics of the Study Population
      Sample Population% Reporting Pain
      Defined as pain on at least some days in the last 3 months.
      ,
      Row percentage; denominator is the number of individuals in each demographic group.
      (Total = 55.7)
      SE
      N (Total = 8,781)Weighted N (Millions) (Total = 234.9)Weighted %
      Column percentage; denominator is the total number of adults. As a result of rounding, in some cases, group percentages do not total 100%.
      (Total = 100)
      SE
      Race, ethnicity, and language of interview
       White
      Non-Hispanic
       English5,393157.667.1.759.7.9
      Hispanic
       English77919.08.1.449.32.3
       Not English55113.35.7.438.42.6
       Black
      Non-Hispanic
       English1,29027.711.8.553.52.0
       Asian
      Non-Hispanic
       English49711.75.0.338.63.0
       Not English35.7.3.129.29.3
       Other race
      individuals who did not self-report as white, black, or Asian as well as those self-reporting as of mixed race.
      Non-Hispanic
       English891.7.7.159.67.1
      Sex
       Male3914113.148.1.753.31.0
       Female4867121.951.9.757.3.9
      Age (y)
       18–443857110.847.2.746.71.1
       45–64303782.135.0.763.31.1
       65 or more187442.017.9.564.71.5
      Number of painful health conditions
      The following potentially painful health conditions were included in the count: abdominal pain, arthritis, back pain, fibromyalgia, gout, jaw pain, joint pain or stiffness, knee problems or stiffness, lupus, muscle or bone pain, neck pain, poor circulation in legs, recurring headache, rheumatoid arthritis, sprain or strain, severe headache or migraine, and other types of chronic pain.
       0245470.530.0.725.11.1
       1169646.019.6.548.01.5
       2124733.314.2.562.21.8
       3 or 4175345.219.2.575.81.2
       5+163140.017.0.590.8.9
      nWeighted N (Millions)Weighted %
      Column percentage; denominator is the total number of adults. As a result of rounding, in some cases, group percentages do not total 100%.
      SE% of Those With Pain
      Column percentage; denominator is the total number of adults with pain on at least some days in the last 3 months.
      SE
      Pain persistence within last 3 months
       None3663100.344.3.7
       Some days325886.638.3.768.7.9
       Most days55314.06.2.411.1.6
       Every day99225.511.1.420.2.8
      Pain bothersomeness for those reporting pain
       A little237362.927.8.649.9.9
       Between a little and a lot149939.817.6.531.6.8
       A lot92623.410.3.418.6.7
      Column percentage; denominator is the total number of adults. As a result of rounding, in some cases, group percentages do not total 100%.
      Defined as pain on at least some days in the last 3 months.
      Row percentage; denominator is the number of individuals in each demographic group.
      § individuals who did not self-report as white, black, or Asian as well as those self-reporting as of mixed race.
      The following potentially painful health conditions were included in the count: abdominal pain, arthritis, back pain, fibromyalgia, gout, jaw pain, joint pain or stiffness, knee problems or stiffness, lupus, muscle or bone pain, neck pain, poor circulation in legs, recurring headache, rheumatoid arthritis, sprain or strain, severe headache or migraine, and other types of chronic pain.
      Column percentage; denominator is the total number of adults with pain on at least some days in the last 3 months.
      Pain prevalence by sex and age is also examined, because these characteristics have previously been shown to be associated with pain prevalence.
      • Hardt J.
      • Jacobsen C.
      • Goldberg J.
      • Nickel R.
      • Buchwald D.
      Prevalence of chronic pain in a representative sample in the United States.
      • Johannes C.B.
      • Le T.K.
      • Zhou X.
      • Johnston J.A.
      • Dworkin R.H.
      The prevalence of chronic pain in United States adults: Results of an Internet-based survey.
      • Portenoy R.K.
      • Ugarte C.
      • Fuller I.
      • Haas G.
      Population-based survey of pain in the United States: Differences among white, African American, and Hispanic subjects.
      • Reyes-Gibby C.C.
      • Aday L.A.
      • Todd K.H.
      • Cleeland C.S.
      • Anderson K.O.
      Pain in aging community-dwelling adults in the United States: Non-Hispanic whites, non-Hispanic blacks, and Hispanics.
      • Riskowski J.L.
      Associations of socioeconomic position and pain prevalence in the United States: Findings from the National Health and Nutrition Examination Survey.
      Age was coded as 18 to 44 years; 45 to 64 years; and 65 years and older.

      Number of Painful Health Conditions

      The 2012 NHIS Adult Core included questions on the presence or absence of 17 health conditions frequently associated with acute, recurring, or chronic pain: abdominal pain, arthritis, back pain, fibromyalgia, gout, jaw pain, joint pain or stiffness, knee problems or stiffness, lupus, muscle or bone pain, neck pain, poor circulation in legs, recurring headache, rheumatoid arthritis, sprain or strain, severe headache or migraine, and other types of chronic pain. From this list, we created a 5-level count variable, which had a roughly quintile distribution: none of the conditions; 1, 2, 3, or 4 conditions; and 5 or more conditions.

      Concurrent Validity

      The concurrent (known-group) validity of the Washington Group pain categories was assessed by examining the relationship of these categories to NHIS questions (see later discussion) that are reasonable surrogates for measures of pain dysfunction.
      • Deyo R.A.
      • Dworkin S.F.
      • Amtmann D.
      • Andersson G.
      • Borenstein D.
      • Carragee E.
      • Carrino J.
      • Chou R.
      • Cook K.
      • DeLitto A.
      • Goertz C.
      • Khalsa P.
      • Loeser J.
      • Mackey S.
      • Panagis J.
      • Rainville J.
      • Tosteson T.
      • Turk D.
      • Von Korff M.
      • Weiner D.K.
      Report of the NIH Task Force on research standards for chronic low back pain.
      Institute of Medicine
      Relieving Pain in American: A Blueprint for Transforming Prevention, Care, Education and Research.
      National Pain Strategy Task Force
      Draft National Pain Strategy.
      • Von Korff M.
      • Dworkin S.F.
      • Le Resche L.
      Graded chronic pain status: An epidemiologic evaluation.
      • Von Korff M.
      • Jensen M.P.
      • Karoly P.
      Assessing global pain severity by self-report in clinical and health services research.
      • Von Korff M.
      • Ormel J.
      • Keefe F.J.
      • Dworkin S.F.
      Grading the severity of chronic pain.
      Physical impairment was assessed with the survey question, “Do you have difficulty walking or climbing steps? Would you say no difficulty, some difficulty, a lot of difficulty, or are you unable to do this?” Data from this question were recoded into 2 categories: 1) no or some difficulty or 2) a lot of difficulty or unable to do.
      Psychological impairment was addressed with 2 survey questions: 1) “Do you take medication for depression?” (Yes, No); 2) “How often do you feel worried, nervous or anxious? Would you say daily, weekly, monthly, a few times a year, or never?” Data from the second question were recoded into 2 categories: 1) less than daily or 2) daily.
      Fatigue was assessed with the survey question, “In the past 3 months, how often did you feel very tired or exhausted? Would you say never, some days, most days, or every day?” Data from this question were recoded into 2 categories: 1) never or some days or 2) most days or every day.
      Health-related unemployment was addressed with the survey question, “I am unable to work NOW due to health problem” (Yes, No)
      Health-related bed-disability days were assessed with the survey question, “During the PAST 12 MONTHS, ABOUT how many days did illness or injury keep you in bed more than half of the day (include days while an overnight patient in a hospital)?” This category was examined both as a continuous variable and as a dichotomous variable (less than 5 days, 5 days or more).
      We also examined the association between the Washington Group pain categories and 3 survey questions measuring health care use: 1) “During the past 12 MONTHS did you receive care from doctors or other health care professionals 10 or more times? Do not include telephone calls” (Yes, No); 2) “How many times did you visit a doctor or other health care professional DURING THE LAST 2 WEEKS?”; and 3) DURING THE PAST 12 MONTHS, HOW MANY TIMES have you gone to a HOSPITAL EMERGENCY ROOM about your own health (This includes emergency room visits that resulted in a hospital admission.)?” The data from the latter 2 questions were treated as both continuous and dichotomous variables: 1) fewer than 2 office visits versus 2 or more office visits or 2) fewer than 4 emergency room visits versus 4 or more visits.
      We assessed the association of the pain categories with a global measure of self-reported health status: “Would you say your health in general is excellent, very good, good, fair, or poor?” Following normal convention, data were recoded into 2 categories: 1) fair or poor or 2) good, very good, and excellent.

      Statistical Analyses

      Contingency tables were used to assess associations between the ordinal pain categories and all other variables. One-way analysis of variance with pain category as the classification variable was used to assess the association of pain category with continuous independent variables: number of comorbid painful health conditions; number of bed-days; number of physician visits in the last 2 weeks; and number of emergency room visits. The χ2 test for linear trends (extended Mantel-Haenszel) was used to assess the association between the ordinal pain categories and dichotomous variables. The Z-test was used to compare individual prevalence rates. All estimates were generated using SUDAAN software (version 9.0; Research Triangle Institute, Research Triangle Park, NC). For inferences about the U.S. population, we used the National Center for Health Statistics sampling weights assigned to the AFD.

      Results

      Table 2 presents selected demographic and health status characteristics of the study population, as well as the proportion of individuals who reported at least some pain in the last 3 months. We found that 44.3% (standard error [SE] .71) of adults, or 100.3 million individuals, were pain free, whereas 126.1 million adults (55.7%, SE .71) reported some pain in the previous 3 months. We found that females, older individuals, and non-Hispanics were more likely to report any pain, whereas Asians were less likely.
      Table 2 also presents the distribution of the adult population according to their response to questions on the persistence and bothersomeness of pain in the previous 3 months. There is a moderate association between pain persistence and bothersomeness (Tau-b = .38, χ2(4) = 824.9, P < .001). The scaling differences between having “a lot of pain” and having “somewhere between a little and a lot of pain” disappear in those with pain every day (chronic pain) (Fig 1). During the 3 months before the survey, 86.6 million adults had pain on some days, 14 million had pain on most days, and 25.5 million had pain every day and are classified as having chronic pain. Of all adults, 62.9 million reported only a little pain, 23.4 million reported a lot of pain, and 39.8 million reported that their pain fell between a little and a lot. An estimated 10.5 million adults reported a lot of pain every day.
      Figure thumbnail gr1
      Figure 1Prevalence of Washington Group pain categories 1 to 4 in the U.S. adult population by pain persistence and bothersomeness.
      Based on the relationship between pain persistence and bothersomeness (Fig 1), 54.1 million adults (23.9% of all adults, SE .59) would be classified as belonging to pain category 1 (least severe); 32.2 million (14.2%, SE .49) to pain category 2; 25.4 million (11.3%, SE .43) to pain category 3; and 14.4 million (6.3%, SE .36) to pain category 4 (most severe).

      Concurrent Validity

      Fig 2 and Table 3 examine the association between the reported number of painful health conditions and the pain categories. The mean number of comorbid health conditions increased from .6 conditions in those with no pain to 6.05 conditions in those with category 4 pain (P < .001). We found that 46% of those with 1 condition did not report any pain in the last 3 months (Fig 2). For those with 5 or more conditions, more than half had either category 3 or category 4 pain. About 2% of those without any painful health conditions had category 3 or 4 pain, and 3.7% of individuals reporting 5 or more health conditions had no pain.
      Figure thumbnail gr2
      Figure 2Association between the reported number of painful health conditions and Washington Group pain categories.
      Table 3Associations Between Pain Categories and Health Status, Health Care Use, and Disability Variables
      Type of MeasurePain CategoriesExtended Mantel-Haenszel χ2dfP Value
      No Pain n = 3663Category 1 n = 2,029Category 2 n = 1,217Category 3 n = 983Category 4 n = 575
      %
      Denominator is the total number of individuals in each pain category.
      SE%
      Denominator is the total number of individuals in each pain category.
      SE%
      Denominator is the total number of individuals in each pain category.
      SE%
      Denominator is the total number of individuals in each pain category.
      SE%
      Denominator is the total number of individuals in each pain category.
      SE
      Health status
       Poor/fair overall health5.4.49.6.816.21.426.11.950.33.1882.54<.001
       Exhausted most/every day2.6.36.9.716.21.325.11.846.42.81020.44<.001
       Taking medication for depression3.7.45.7.612.91.216.61.431.72.7482.84<.001
       Worried, nervous, anxious every day4.1.45.3.610.11.014.81.428.32.8365.44<.001
      Health care use
       Received medical care ≥10 times in last year5.1.410.1.815.21.324.11.738.52.4580.94<.001
       ≥2 office visits with health professional in last 2 weeks2.7.33.9.56.4.99.91.217.72.0426.64<.001
       ≥4 visits to emergency room in last year.5.1.6.22.3.64.71.010.11.5532.54<.001
      Disability
       Unable to work because of health problem2.3.34.3.58.817.81.636.72.5709.74<.001
       A lot of difficulty walking or climbing steps1.22.7.45.2.711.41.228.32.21441.98<.001
       ≥5 bed-disability days6.58.9.817.41.4241.537.82.4701.216<.001
      No PainCategory 1Category 2Category 3Category 4
      Mean
      Denominator is the total number of individuals in each pain category.
      SDMean
      Denominator is the total number of individuals in each pain category.
      SDMean
      Denominator is the total number of individuals in each pain category.
      SDMean
      Denominator is the total number of individuals in each pain category.
      SDMean
      Denominator is the total number of individuals in each pain category.
      SDF
      F statistic calculated from 1-way ANOVA.
      dfP Value
      Health status
       Number of painful health conditions.61.212.052.253.333.144.453.456.053.611074<.001
      Health care use
       Number of health professional visits in last 2 weeks.17.55.24.61.35.81.561.34.741.13102.54<.001
       Number of visits to the emergency room in last year.21.78.27.79.461.08.691.491.362.52149.94<.001
      Disability
       Number of health-related bed-disability days in last year1.4611.032.4114.454.822.97.7127.8715.2638.3974.54<.001
      Denominator is the total number of individuals in each pain category.
      F statistic calculated from 1-way ANOVA.
      Fig 3 and Table 3 show the relationship between the pain categories and other measures of health status. As one moves to successively more severe pain states, there is increased probability of being in a poorer health state. For instance, although 5.4% of individuals reporting no pain rated their overall health as poor or fair, this increased to 9.6 in those with category 1 pain, 16.2% in those with category 2 pain, 26.1% in those with category 3 pain, and 50.3% in those with category 4 pain (P < .001) Similarly, those with category 4 pain were more likely to report being exhausted most or every day (46.4%), to be taking medication to treat their depression (31.7%), and to be worried, nervous, or anxious every day (28.3%).
      Figure thumbnail gr3
      Figure 3Association between Washington Group pain categories and measures of health status.
      The association between pain category and disability is shown in Fig 4 and Table 3. The number of bed-disability days increased from 1.46 days in those with no pain to 15.26 days in those with category 4 pain (P < .001). Similarly, 38.7% of those with category 4 pain had at least 5 bed-disability days versus 6.0% of those with no pain. Although 2.3% of those without pain were unable to work for health reasons, this increased to 36.7% in those with category 4 pain. Those with category 4 pain were more likely to have a lot of difficulty walking or climbing steps (28.3%) versus those in lower pain states.
      Figure thumbnail gr4
      Figure 4Association between Washington Group pain categories and measures of disability.
      Fig 5 and Table 3 show that individuals in more severe pain have greater use of health care than those in less severe pain. A significant increase was seen in the number of visits to a health profession within the previous 2 weeks (P < .001), with a mean of .17 visits seen in those not reporting pain to .74 visits seen in those with category 4 pain. Similarly, 17.7% of those with category 4 pain had 2 or more office visits in the previous 2 weeks versus 2.7% in those not reporting pain (P < .001). Individuals with category 4 pain were likely to have had 4 or more visits to the emergency room in the last year (10.1%) and to have received medical care 10 or more times in the last year (38.5%) compared with those in lower pain states (P < .001).
      Figure thumbnail gr5
      Figure 5Association between Washington Group pain categories and measures of healthcare utilization.

      Demographic Variables

      The distribution of pain categories across language/ethnic/racial groups was consistent with prevalence decreasing as one moves to more severe pain categories (Fig 6). Despite this similarity, some significant differences between groups were noted. NHA who preferred English and HW who did not prefer English were significantly more likely to be pain free than NHW who preferred English (P < .001), NHB who preferred English (P < .001), HW who preferred English (P = .004), and non-Hispanic individuals who did not self-report as white, black, or Asian who preferred English (P = .007). NHA who preferred English and HWNE were also 1) significantly less likely to have category 3 pain (P < .001) than NHW who preferred English, NHB who preferred English, and HW who preferred English and 2) less likely to have category 4 pain than NHW who preferred English (P = .004) and NHB who preferred English (P = .011).
      Figure thumbnail gr6
      Figure 6Distribution of Washington Group pain categories across selected language/ethnic/racial groups.
      We further explored whether the observed differences in pain severity between language/ethnic/racial groups were consistent across the reported number of painful health conditions. As shown in Fig 7, for each demographic group except HWNE, the prevalence of category 3 or 4 pain is substantially higher in those with 5 or more conditions compared with those with 3 or 4 conditions (P < .05). It was found that HWNE with 5 or more health conditions had lower prevalence of category 3 or 4 pain than NHW who preferred English (P = .006). No difference was noted between HWNE and any other group.
      Figure thumbnail gr7
      Figure 7Impact of the number of painful health conditions on the prevalence of category 3 or 4 pain across selected language/ethnic/racial groups.
      The impact of sex and age on the prevalence of category 3 or 4 pain varies by the specific language/ethnic/racial group. Although female NHW who preferred English and female NHB who preferred English have higher rates of category 3 or 4 pain than males (P < .001 and P = .016, respectively), no gender difference was seen for the other language/ethnic/racial group (Fig 8). Although 18-year-olds to 44-year-olds had a lower prevalence of category 3 or 4 pain then older age groups across language/ethnic/racial groups (Fig 9), no difference was seen between individuals 45 to 64 years old and 65 years or older. HWNE and NHA aged 18 to 44 years who preferred English had substantially lower rates of category 3 or 4 pain compared with this same age group in NHW who preferred English, HW who preferred English, and NHB who preferred English (P < .001). In subjects aged 45 to 64 years, NHA who preferred English also had substantially lower rates of category 3 or 4 pain than NHW who preferred English and NHB who preferred English. No other age differences were seen between language/ethnic/racial groups.
      Figure thumbnail gr8
      Figure 8Impact of sex on the prevalence of category 3 or 4 pain across selected language/ethnic/racial groups.
      Figure thumbnail gr9
      Figure 9Impact of age on the prevalence of category 3 or 4 pain across selected language/ethnic/racial groups.

      Discussion

      Using data from a large national survey, we estimated that 55.7% of American adults (approximately 126 million individuals) reported having some level of pain within the 3 months before the survey. Substantially fewer individuals (11.2% or 25.5 million adults) had experienced chronic pain (pain every day for the past 3 months), a lot of pain (10.3% or 23.4 million adults), or were coded to the most severe Washington Group pain category (category 4: 6.3% or 14.4 million adults).
      This study provides evidence on the concurrent (known-group) validity of the Washington Group pain categories in the general population, in that the pain categories clearly discriminate between different levels of health status, disability, and health care use. Although there was a strong relationship between pain categories and both health status and disability variables, about 50% of individuals with category 4 pain still reported their overall health status as good or better. This finding is similar to findings by Von Korff and colleagues
      • Von Korff M.
      • Ormel J.
      • Keefe F.J.
      • Dworkin S.F.
      Grading the severity of chronic pain.
      and Kamaleir and colleagues,
      • Kamaleri Y.
      • Natvig B.
      • Ihlebaek C.M.
      • Benth J.S.
      • Bruusgaard D.
      Number of pain sites is associated with demographic, lifestyle, and health-related factors in the general population.
      who used different measures of pain severity. In a series of studies examining the impact of multiple painful musculoskeletal sites, Kamaleri and colleagues
      • Kamaleri Y.
      • Natvig B.
      • Ihlebaek C.M.
      • Benth J.S.
      • Bruusgaard D.
      Number of pain sites is associated with demographic, lifestyle, and health-related factors in the general population.
      found that about 50% of individuals reporting as many as 10 painful musculoskeletal sites still rated their overall health status as good or better. In an early evaluation of the Chronic Pain Grade, Von Korff and colleagues
      • Von Korff M.
      • Ormel J.
      • Keefe F.J.
      • Dworkin S.F.
      Grading the severity of chronic pain.
      found that many individuals with a Chronic Pain Grade of IV (most severe) still reported their overall health status as good or better: 45% in those with temporomandibular pain, 75.3% in those with headache, and 79.4% in those with back pain. These data show the heterogeneity of responses to pain even in those with similar levels of pain.
      The Washington Group pain category approach used in this analysis has both substantial strengths and limitations. The approach has been tested and validated in a number of countries using a variety of qualitative assessments, such as cognitive testing,
      • Madans J.H.
      • Loeb M.E.
      • Altman B.M.
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      • Madans J.H.
      • Loeb M.
      Methods to improve international comparability of census and survey measures of disability.
      • Miller K.
      • Loeb M.
      Mixed-Method Assessment of Validity and Cross-Subgroup Comparability. AAPOR 69th Annual Conference.

      Washington Group on Disability Statistics. Available at: http://www.cdc.gov/nchs/washington_group.htm. Accessed April 23, 2015

      and, as shown in the present report, has concurrent validity. Importantly, the category assignment is based on just 2 questions. This brevity makes it easy to understand and to apply the scoring system and should ease its inclusion into epidemiologic studies in which participant burden is already high. In this regard, the approach has met many of the criteria that Elliott and colleagues
      • Elliott A.M.
      • Smith B.H.
      • Chambers W.A.
      Measuring the severity of chronic pain: A research perspective.
      suggest for measures of chronic pain severity in epidemiologic research: be brief, be simple, be acceptable, be reliable, and ask about appropriate duration of symptoms. However, the Washington Group pain categories have not yet been evaluated using psychometric approaches and clearly do not meet a critical criterion for a pain scale: multidimensionality. By multidimensional, Elliott and colleagues
      • Elliott A.M.
      • Smith B.H.
      • Chambers W.A.
      Measuring the severity of chronic pain: A research perspective.
      specifically mean the “psychological and social dimensions of chronic pain” and cite trying to combine multidimensionality with simplicity and brevity as the great challenge in designing new pain measures. Of the current pain measures, perhaps the one that comes closest to balancing brevity and multidimensionality is the Chronic Pain Grade approach developed and initially validated by Von Korff and colleagues,
      • Von Korff M.
      • Ormel J.
      • Keefe F.J.
      • Dworkin S.F.
      Grading the severity of chronic pain.
      with subsequent replication completed across multiple countries,
      • Elliott A.M.
      • Smith B.H.
      • Penny K.I.
      • Smith W.C.
      • Chambers W.A.
      The epidemiology of chronic pain in the community.
      • Klasen B.W.
      • Hallner D.
      • Schaub C.
      • Willburger R.
      • Hasenbring M.
      Validation and reliability of the German version of the Chronic Pain Grade questionnaire in primary care back pain patients.
      • Wong W.S.
      • Fielding R.
      Prevalence and characteristics of chronic pain in the general population of Hong Kong.
      for both cross-sectional and longitudinal purposes,
      • Bruhn H.
      • Bond C.M.
      • Elliott A.M.
      • Hannaford P.C.
      • Lee A.J.
      • McNamee P.
      • Smith B.H.
      • Watson M.C.
      • Holland R.
      • Wright D.
      Pharmacist-led management of chronic pain in primary care: Results from a randomised controlled exploratory trial.
      • Elliott A.M.
      • Smith B.H.
      • Hannaford P.C.
      • Smith W.C.
      • Chambers W.A.
      The course of chronic pain in the community: Results of a 4-year follow-up study.
      • Elliott A.M.
      • Smith B.H.
      • Smith W.C.
      • Chambers W.A.
      Changes in chronic pain severity over time: The Chronic Pain Grade as a valid measure.
      • Khan F.
      • Amatya B.
      • Kesselring J.
      Longitudinal 7-year follow-up of chronic pain in persons with multiple sclerosis in the community.
      • Ohrbach R.
      • Turner J.A.
      • Sherman J.J.
      • Mancl L.A.
      • Truelove E.L.
      • Schiffman E.L.
      • Dworkin S.F.
      The Research Diagnostic Criteria for Temporomandibular Disorders. IV: Evaluation of psychometric properties of the Axis II measures.
      and in both the general population and clinical cohorts.
      • Bruhn H.
      • Bond C.M.
      • Elliott A.M.
      • Hannaford P.C.
      • Lee A.J.
      • McNamee P.
      • Smith B.H.
      • Watson M.C.
      • Holland R.
      • Wright D.
      Pharmacist-led management of chronic pain in primary care: Results from a randomised controlled exploratory trial.
      • Khan F.
      • Amatya B.
      • Kesselring J.
      Longitudinal 7-year follow-up of chronic pain in persons with multiple sclerosis in the community.
      • Klasen B.W.
      • Hallner D.
      • Schaub C.
      • Willburger R.
      • Hasenbring M.
      Validation and reliability of the German version of the Chronic Pain Grade questionnaire in primary care back pain patients.
      • Ohrbach R.
      • Turner J.A.
      • Sherman J.J.
      • Mancl L.A.
      • Truelove E.L.
      • Schiffman E.L.
      • Dworkin S.F.
      The Research Diagnostic Criteria for Temporomandibular Disorders. IV: Evaluation of psychometric properties of the Axis II measures.
      • Von Korff M.
      • Ormel J.
      • Keefe F.J.
      • Dworkin S.F.
      Grading the severity of chronic pain.
      When developing this approach, Von Korff and colleagues
      • Von Korff M.
      • Dworkin S.F.
      • Le Resche L.
      Graded chronic pain status: An epidemiologic evaluation.
      • Von Korff M.
      • Ormel J.
      • Keefe F.J.
      • Dworkin S.F.
      Grading the severity of chronic pain.
      considered several additional criteria not listed by Elliot and colleagues
      • Elliott A.M.
      • Smith B.H.
      • Chambers W.A.
      Measuring the severity of chronic pain: A research perspective.
      : 1) be a mutually exclusive and exhaustive set of ordered categories of rank, which correspond to qualitative differences in chronic pain severity; 2) be an important indicator of chronic pain severity and ability to predict patient outcomes; and 3) be generalizable across different anatomical sites and heterogeneous causes of chronic pain. In the present report, we have shown that the Washington Group approach meets some of these criteria by producing discrete ordinal categories that can discriminate levels of health status, health care use, and disability. However, to fully meet the 2 sets of criteria listed earlier, some additional studies are needed to explore the Washington Group approach, including, but not limited to 1) psychometric analyses to confirm the category cutoffs identified in qualitative and mixed-method studies; 2) longitudinal studies to assess changes in the pain severity category over time and the predictors of this change; 3) direct comparisons with established measures of pain and function, including but not limited to the Chronic Pain Grade, PROMIS (Patient Reported Outcomes Measurement Information System) measures of pain, and the Short Form-36 questionnaire (especially, body pain domain); 4) studies to assess the usefulness of the Washington Group pain categories in the clinic to aid diagnosis, guide treatment, and assess treatment outcomes; and 5) exploration of the usefulness of the Washington Group approach in pediatric populations and other populations who might require a proxy respondent.
      Although the Washington Group approach and the Chronic Pain Grades appear similar on first glance in that both divide pain status into 5 (including no pain) discrete ordinal categories, the domains creating the pain categories and grades differ substantially. The Washington Group categorization is based on questions assessing pain persistence and bothersomeness (which is related to pain intensity), whereas the Chronic Pain Grades I to IV are assigned based on pain intensity and pain-related disability. Originally, Von Korff and colleagues
      • Von Korff M.
      • Dworkin S.F.
      • Le Resche L.
      Graded chronic pain status: An epidemiologic evaluation.
      • Von Korff M.
      • Ormel J.
      • Keefe F.J.
      • Dworkin S.F.
      Grading the severity of chronic pain.
      had considered pain persistence as an additional fact in grade assignment, but psychometric analysis found
      • Von Korff M.
      • Ormel J.
      • Keefe F.J.
      • Dworkin S.F.
      Grading the severity of chronic pain.
      that persistence “was inconsistently and weakly associated with intensity and disability,” and that “it did not appear that the product of pain intensity and pain persistence substantially increase the prediction of threshold at which significant disability was present.” Persistence was eliminated from the scale. In the present analysis, we found that overall persistence had a moderate association with bothersomeness, but that the scaling differences between having “a lot of pain” and having “somewhere between a little and a lot of pain” disappear in those with pain every day (chronic pain). The differences in the present finding and that of Von Korff and colleagues
      • Von Korff M.
      • Dworkin S.F.
      • Le Resche L.
      Graded chronic pain status: An epidemiologic evaluation.
      • Von Korff M.
      • Ormel J.
      • Keefe F.J.
      • Dworkin S.F.
      Grading the severity of chronic pain.
      might have several explanations, most especially differences in how pain persistence and intensity (bothersomeness) were assessed. For instance, in the Washington Group approach, bothersomeness was based on a single question with only 3 options (a little pain, between a little and a lot of pain, and a lot of pain), whereas the Chronic Pain Grades averaged 0 to 10 ratings of pain right now, average pain (last 6 months), and worst pain (in the last 6 months). Given these differences, additional studies are needed to directly compare the 2 pain assessment approaches.
      Our finding that 55.7% of adults reported any pain is a higher prevalence rate than reported in previous U.S. national surveys. The difference probably reflects the questions used to assess pain. The initial pain question in the 2012 NHIS simply asked if the participant had pain in the last 3 months, without any qualifiers. Studies using National Health and Nutrition Examination Survey (NHANES) data reported prevalence ranging from 26 to 34%,
      National Center for Health Statistics
      Health, United States, 2006 With Chartbook on Trends in the Health of Americans.
      • Riskowski J.L.
      Associations of socioeconomic position and pain prevalence in the United States: Findings from the National Health and Nutrition Examination Survey.
      • Slade G.D.
      • Sanders A.E.
      • By K.
      Role of allostatic load in sociodemographic patterns of pain prevalence in the U.S. population.
      but the initial question asked participants if they had any pain within the last month that lasted at least 24 hours. Data from the Health and Retirement Study
      • Reyes-Gibby C.C.
      • Aday L.A.
      • Todd K.H.
      • Cleeland C.S.
      • Anderson K.O.
      Pain in aging community-dwelling adults in the United States: Non-Hispanic whites, non-Hispanic blacks, and Hispanics.
      produced similar prevalence rates (27–33%) to NHANES estimates. The Health and Retirement Study also qualified its question on pain by asking participants if they “were often troubled with pain.” In contrast, national surveys of the general population that have collected information on more severe pain (eg, visual analog scale score of 8 or above) found prevalence rates between 7 and 11%,
      • Banks J.
      • Kapteyn A.
      • Smith J.P.
      • van Soest A.
      Work disability is a pain in the ****, especially in England, the Netherlands, and the United States.
      • Gaskin D.J.
      • Richard P.
      The economic costs of pain in the United States.
      • Johannes C.B.
      • Le T.K.
      • Zhou X.
      • Johnston J.A.
      • Dworkin R.H.
      The prevalence of chronic pain in United States adults: Results of an Internet-based survey.
      consistent with our observation that 10.3% of adults reported a lot of pain. Similar to our data, analysis of NHANES data consistently estimated chronic pain (pain ≥3 months) prevalence at 13 to 15%.
      • Dansie E.J.
      • Turk D.C.
      • Martin K.R.
      • Van Domelen D.R.
      • Patel K.V.
      Association of chronic widespread pain with objectively measured physical activity in adults: Findings from the National Health and Nutrition Examination Survey.
      • Hardt J.
      • Jacobsen C.
      • Goldberg J.
      • Nickel R.
      • Buchwald D.
      Prevalence of chronic pain in a representative sample in the United States.
      • Riskowski J.L.
      Associations of socioeconomic position and pain prevalence in the United States: Findings from the National Health and Nutrition Examination Survey.
      The slightly lower rate we observed (11.1%) most likely results from our requirement that defined chronic pain as daily pain. These consistencies across national surveys reinforce our confidence that the pain questions in the NHIS provide reliable national estimates of pain prevalence.
      To the best of our knowledge, these are the first data to assess the interactions of race, ethnicity, and language preference in relation to pain severity. In contrast to the present results, the 2 previous national studies of which were are aware that considered the impact of language
      • Jimenez N.
      • Dansie E.
      • Buchwald D.
      • Goldberg J.
      Pain among older Hispanics in the United States: Is acculturation associated with pain?.
      • Portenoy R.K.
      • Ugarte C.
      • Fuller I.
      • Haas G.
      Population-based survey of pain in the United States: Differences among white, African American, and Hispanic subjects.
      did not find associations between the use of Spanish or English and pain. However, these studies differed from the present report in several substantial ways. Portenoy and colleagues
      • Portenoy R.K.
      • Ugarte C.
      • Fuller I.
      • Haas G.
      Population-based survey of pain in the United States: Differences among white, African American, and Hispanic subjects.
      collected data only from whites, blacks, and Hispanics and limited the regression analysis to those with disabling pain (both high pain severity and high life interference). The Health and Retirement Study analyzed by Jimenez and colleagues
      • Johannes C.B.
      • Le T.K.
      • Zhou X.
      • Johnston J.A.
      • Dworkin R.H.
      The prevalence of chronic pain in United States adults: Results of an Internet-based survey.
      was limited to participants at least 50 years old who were “often troubled by pain.” In addition, neither of these studies presented age-specific and sex-specific prevalence rates of pain in whites and minority groups. Thus, although both studies present unique insights into specific populations, they do not reflect the association between race, ethnicity, and language and the spectrum of pain in the U.S. adult population.
      The current study has several limitations beyond those already mentioned. First, because these are cross-sectional data, the study cannot assess clinical outcomes associated with pain severity. Second, because the NHIS did not collect pain treatment information, we were unable to determine whether differences in treatment could have further explained the difference in pain experiences of the participants. Third, although the NHIS sampling design allows for unbiased estimates of national trends, the data are limited to the noninstitutionalized population. Future research should consider nationally representative pain assessment for persons in nursing home, hospice, and other residential health care facilities, because these persons are likely to be disproportionately affected by chronic conditions. Because of sample size limitations, 1) we were not able to examine Asians and Hispanic subpopulations (eg, Koreans, Chinese, Puerto Ricans, Mexicans), who vary in their underlying health status
      • Barnes P.M.
      • Adams P.F.
      • Powell-Griner E.
      Health characteristics of the Asian adult population: United States, 2004–2006.
      • Jerant A.
      • Arellanes R.
      • Franks P.
      Health status among US Hispanics: Ethnic variation, nativity, and language moderation.
      ; 2) we were not able to examine Native Americans, Native Alaskans, Native Hawaiians, and Pacific Islanders individually but had to combine them into a single group; and 3) we had to code preferred languages into 2 broad groups: those who preferred English and those who preferred another language.
      In 2012, nearly 40 million adults (17.6% of all adults) were classified as falling within the 2 most severe Washington Group pain categories (3 and 4). Individuals with category 3 or 4 pain were more likely to have worse health status, to use more health care, and to suffer from more disability than those with less severe pain. Associations were seen between pain severity and selected demographic variables, including race, ethnicity, preferred language, sex, and age. Although these data are promising, additional work is required to determine the usefulness of the Washington Group pain categories for pain research or clinical practice.

      Acknowledgments

      The author thanks Dr. Laura Lee Johnson, PhD, of National Center for Complementary and Integrative Health (NCCIH), National Institutes of Health for her statistical advice, Ms. Danita Byrd-Clark, BBA, of Social & Scientific Systems, for her programming skills, Mr. Bryan Ewsichek, BA, of NCCIH, National Institutes of Health for his help with graphic design, and the many NCCIH staff who read and commented on earlier versions of this work.

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