Many readers have questioned the latest figure that 116 million American adults suffer from chronic pain, which represents more than a third of the total population. Yet, looking at the original source of this data, the evidence seems generally reliable and, furthermore, the U.S. is not unique in the world — chronic pain seems to be a truly huge problem of global proportions.
That 116 million estimation of chronic pain in the U.S. comes from a lengthy Institute of Medicine (IOM) report released last June, 2011: Relieving Pain in America: A Blueprint for Transforming Prevention, Care, Education, and Research [discussed in UPDATE here]. Apparently, many healthcare providers and opinion leaders find that number a bit far-fetched. Where did it come from and can it be trusted as being valid?
ADDENDUM 3/20/2012 — In March 2012, the Institute of Medicine revised their report to state that an estimated 100 million U.S. adults experience chronic pain, and not the 116 million as stated in the original report "Relieving Pain in America" . This is consistent with the 101 million that we calculate below, and it is still a very significant number that does not include children, veterans, or persons who are institutionalized. --SBL
A Global Pandemic of Chronic Pain?
We found that the IOM report lists a single reference for their 116 million estimate; a study by Adley Tsang and an international team of researchers appearing in the October 2008 edition of the Journal of Pain [Tsang et al. 2008]. This was a monumental investigation, supported by dozens of government and non-government organizations, and spanning 10 developed and 7 developing countries. Goals of the study were to determine the prevalence by age and gender of common chronic pain conditions (headache, back or neck pain, arthritis or joint pain, and others), plus their association with both depressive and anxiety disorders.
Using the same questionnaire and face-to-face interviews, 18 surveys were carried out in 17 countries:
- Developing countries included China, Columbia, Lebanon, Mexico, Nigeria, South Africa, and Ukraine.
- Developed countries included Belgium, France, Germany, Israel, Italy, Japan, Netherlands, New Zealand, Spain, and the United States.
In the sample of 42,249 interviews included for analysis most of the respondents were at age 18 or older (except Japan ≥20 years of age; Israel ≥21; and New Zealand ≥16). The researchers found that that the overall age-standardized prevalence of chronic pain conditions in the prior 12 months was 37.3% in developed countries and 41.1% in developing countries [see figure]. After including chronic pain associated with anxiety/depression, and controlling for comorbid chronic physical diseases, several findings were evident:
- The overall age-standardized prevalence of chronic pain was 43.4% in the 17 countries studied (total bar on left).
- The prevalence of chronic pain conditions was consistently higher among females, and also significantly greater in older persons >age 65 (not shown in figure).
- Chronic pain was similarly associated with depression and anxiety disorders in both developed and developing countries (shaded portions of bars); however, the vast majority of persons reporting chronic pain did not meet criteria for these disorders (clear portions of bars).
If these 17 countries are considered representative of the worldwide population, it could be reasonable to say that chronic pain is endemic globally. Tsang and colleagues observe that prevalence rates in various earlier surveys ranged from 17% to 29% in west central Europe, and from 2% to 40% in one review of surveys in developed countries. A large-scale epidemiological study covering western, northern, and central Europe and Israel had found that 19% of respondents reported moderate or severe pain of at least 6 months' duration. We had reported on studies conducted in different parts of the world that found prevalence rates of chronic pain ranging from 12% to 80% [see UPDATE here]. Some of the reports seem to suggest that chronic pain may be increasing worldwide, and if this is the case the problem might be described as being of pandemic proportions
Chronic Pain Epidemic in America?
In their report, other than referencing the Tsang et al.  study, the IOM committee does not indicate the calculations they used to arrive at the 116 million number. In attempting to determine its origins, we examined the following data:
- U.S. Census Bureau [here] estimates the U.S. population in 2010 was about 309 million persons. Of these, roughly 76% were ≥18 years old, or 235 million adults.
- The Tsang et al. study indicates that the age-standardized prevalence of chronic pain in U.S. adults was 43%. This suggests a number of only about 101 million adults (.43 x 235 million).
- However, this does not include the proportion of subjects with chronic pain + anxiety/depression, and this number is unclear in the Tsang et al. data. If the IOM committee used a figure of 6% for this proportion (which is somewhat consistent with data in the figure above), making a total of 49% of all adults having chronic pain, the number does come out to roughly 116 million (based on 2010 census data).
- Another possibility is that the IOM committee used a figure greater than 309 million for the U.S. population for their calculations, since this is an ever-changing and increasing number. In this case, somewhat less than 49% of adults could be considered as having chronic pain.
So, there are certain unknown factors in the IOM estimation. However, it seems clear that, based on available evidence, the problem of chronic pain in America actually does affect a much larger proportion of adults — probably more than 45% of adults and in excess of 100 million persons at the least — than many people want to believe.
Earlier reports on chronic pain in America have suggested lower numbers. Several years ago, the American Pain Foundation (APF) estimated that 26% of Americans age ≥20 (76.5 million persons) had chronic pain to some extent, and in November 2010 we reported that 78 million adults suffered chronic pain lasting ≥3 months, or 72 million with pain lasting 6 months or longer [UPDATE here]. So, the latest estimate of 116 million adults from the IOM and background data convey that this may be a growing problem affecting a disproportionately large number of individuals within the U.S. population — this is the definition of an epidemic.
Strengths & Weaknesses
As with any survey research, there were strengths and weaknesses of the Tsang et al. study, which in turn affected accuracy of the IOM committee estimation. An important strength was that the prevalence of chronic pain was based on results from a large number of population surveys executed using rigorous sampling methods and a uniform questionnaire. A second strength was in controlling for variations in chronic physical and mental diseases, age, and gender across countries.
A potential weakness, or limitation, to be considered is whether a sample size of 42,249, covering 18 surveys in 17 countries, was sufficient. Certainly, only a relatively small and select portion of the populations were represented.
Another limitation was in how chronic pain conditions were assessed. Tsang and colleagues indicate that, using a standard checklist appropriately translated into different languages, respondents were asked if they ever had “arthritis or rheumatism” in their lifetime, and were then asked if this had been present in the prior 12 months. They were further asked whether they ever had “chronic back or neck problems,” “frequent or severe headaches,” and/or “other chronic pain” in the prior 12 months.
The authors concede that chronic pain may not have been adequately defined and some responses might have reflected misunderstandings of the specific pain conditions as well as their severity, frequency, and duration. However, a major strength of the study countering this and helping to ensure accuracy was that interviews were conducted face-to-face by persons specially trained in each country to survey subjects. So, it might be expected that overall categorizations of chronic pain versus no chronic pain in those interviewed were probably valid.
REFERENCE: Tsang A, Von Korff M, Lee S. et al. Common Chronic Pain Conditions in Developed and Developing Countries: Gender and Age Differences and Comorbidity With Depression-Anxiety Disorders. J Pain. 2008(Oct);9(10):883-891 [abstract here].