Everybody Hurts: Why Pain Is Not the Same at Every Age and in Every Place
In the 1999 Scotland study published in the Lancet that has become a basis for some claims that up to 150 million Americans suffer from chronic pain and yet very few are treated for it, there is a key sentence that seems to be missed by those citing it:
Prevalence of chronic pain also varies widely across different geographical locations.
The citation for that statement is a 1998 paper in the Journal of the American Medical Association (JAMA) that looked at pain prevalence in 15 health centers in 14 countries around the world. It studied the prevalence of “persistent pain,” which it defined as pain that was “present most of the time for a period of 6 months or more during the prior year.”
It found that 22% of primary care patients reported “persistent pain.” That’s less than half of the rate of “chronic pain” found in the Scotland study, which it defined as “continuous or intermittent pain or discomfort which has persisted for at least 3 months. (I’ll get into the definitional issues, like the difference between “persistent pain” and “chronic pain” in a later post.)
The JAMA study also found huge variation across the centers, ranging from 5.5% to 33%. The one center that participated in the U.S. was in Seattle, and it found a prevalence of 17.3%. Note, too, that in no center was the prevalence rate as high as 46.5%, which was the Scotland chronic pain prevalence rate.
I emailed the lead researcher on the Scotland study, Dr. Alison Elliott at the University of Aberdeen in Scotland, to ask her about how her study had become the basis for the 150 million claim. The first thing she told me was, “We do not make any reference to the numbers of people in the U.S. suffering from chronic pain in our Lancet paper.”
She, like me, had to make a best guess as to why her study is being used to make that claim. She wrote:
I suspect that our prevalence figure of 50.4% is being applied to the U.S. population to come up with the estimate of 75-150 million people in the U.S.. Large scale epidemiological studies are rare and costly and as a result prevalence figures from studies conducted in other countries are sometimes used to make estimates for countries where studies have not taken place.
The 50.4% figure is what the Scotland researchers found before adjusting the estimate they found from their survey sample to apply it to the general population in Scotland. And now the most important question: Does it make sense to take chronic pain estimates from Scotland – whether it’s 50.4% or 46.5% – and apply those estimates to the U.S.? Eliott recommended against it.
Prevalence estimates of any condition are hugely influenced by a number of factors including the population studied, time of study, definition used, research methods, measurement instruments used etc., all of which vary from study to study. Extrapolating figures from one country to another is difficult and should be undertaken with extreme caution since different populations will have different age distributions, different socio-economic circumstances, different cultures may experience conditions differently etc. For example, in our study the prevalence of chronic pain increased with age from 31.7% for the youngest age group (25-34 year olds) to 62.0% for the oldest age group (75 and older). So countries with a relatively young population would be likely to have a lower prevalence of chronic pain than countries with an older population. We cannot say anything about the prevalence of chronic pain in those under 25 since we didn’t include these ages in our study.
Remember, that when you apply a prevalence rate like 46.5% to a population of 309 million in the U.S., you are including a lot of young people. Taking out everyone under 25 would remove more than one-third of the population: 105 million people. That leaves about 204 million people, 46.5% of which is 95 million. That’s still a lot of people in a lot of pain, but instead of every other person in pain, it becomes closer to 1 out of 3. Does that still seem high?
Here’s another factor to consider. When we talk about pain, the definition matters quite a bit. Elliott made this point in her email to me, and I’m going to expand on it in my next post.
Next: Chronic Pain Is In the Body of the Sufferer
Image by Deborah Leigh via Flickr