Questioning One in Four: Part 1

Link - Part 2, Part 3

One in four people suffer mental illness at some point in their lives.

Everyone knows that. But where does that number come from? The answer may surprise. Join me, if you will, as I explore the biography of a statistic.

"1 in 4" is ubiquitous, at least in the English-speaking world. I can't think of another such number which is better known, except perhaps the fact that 1 in 3 people will suffer from cancer.

Anyone who's used the London Underground or watched British TV recently will be familiar with the Time to Change anti-stigma advertising drive. This £18 million campaign, run by the charities Mind and Rethink, is awash with "1 in 4"s, left right and center. Mind have it on their About Us page. The BBC have it on their main mental health page. There's even a One in Four magazine. And so on.

In the next post, I'll be examining the truth behind this statistic, but first, a little history. Google archive reveals that 1 in 4 is a child of the 1990s. English-language news media from the late 1980s contain the statement that in 1 in 4 (American) families will have a member who suffers from mental illness, but this is not the same thing.

As far as I can tell, "1 in 4 people" entered the popular mind in the early to mid 1990s. By 1995, it was common and being referred to as an accepted fact. See for example this snap-shot of the newspapers in 1995 under the search term ("one in four" + mental), showing that the idea had taken root by this point. Whereas the equivalent from 1992 is quite different.

Interestingly, the early 1990s also feature repeated references to 1 in 4 (Americans) suffering from mental illness in any given year; this statistic, however, gradually fades from view as the decade goes on. By 2000, 1 in 4 appears more often than ever, but now it refers almost mostly to lifetime prevalence.

These graphs show the number of Google archive hits from 1950 to 2008. I had hoped that this would illustrate my argument nicely, but sadly, the picture isn't all that clear. Here it is anyway - the top graph shows the increase in ("1 in 4" + mental) hits. The second shows, by way of comparison, the number of hits for just ("mental health"), which is much more level. That's nice. But the bottom graphs shows that ("1 in 8" + mental) also becomes more popular over about the same time-frame, which is a bit confusing, as 1 in 8 is not a number especially linked to mental health.

But - where did 1 in 4 come from? When I set out to write this post, I thought it would be fairly easy to find out, but having done a lot of digging, I genuinely don't know.

My first guess was that it must have been the National Comorbidity Survey (NCS). The NCS was an ambitious attempt to measure the prevalence of mental disorders in a representative sample of the U.S. population, masterminded by Harvard Prof. Ronald C. Kessler. Data collection took place between 1990 - 1992 and the results started to be published in 1993 - just about the time when 1 in 4 started to appear in the media.

But in fact the headline finding from the NCS, as published in 1994, was that the lifetime prevalence of mental disorders was nearly 50%! That's 1 in 2 (sic). The proportion estimated to suffer from a disorder in any given year was almost 1 in 3. But no sign of 1 in 4.

Meanwhile, in Britain, 1993 also saw the first Psychiatric Morbidity Survey, a similar enterprise. (Attentive Neuroskeptic fans will recall that this was the survey that the Mental Health Foundation recently distorted to make it look like rates of anxiety disorders are rising). Could this be the source? No, the headline number here was 1 in 6, which referred to mental illness in the past week, not over the lifetime.

Going further back, the Epidemiological Catchment Area (ECA) project, the first large-scale psychiatric epidemiology study, happened in the early 80's. The ECA famously concluded that 1 in 3 Americans suffer at least one mental illness over the lifetime, and 1 in 5 do in any given six month period! 3, 5 - but still not 4.


The World Health Organization quoted 1 in 4 lifetime in 2001, to much media fanfare, and I have seen the WHO given as a source for the figure. But where did they get it from? Well, good question.

Their report, New Understanding New Hope: The World Health Report 2001, notes that according to the WHO's own data, 450 million people worldwide currently suffer from a "neuropsychiatric conditions". With 6 billion people on Earth that's less than 1 in 12 (and that includes Alzheimer's, Parkinson's, epilepsy, etc.) And that's at any one time, not over the whole lifetime.

The report then quotes at least 1 in 4 as a lifetime prevalence (on page 23). Finally! But this is not based on WHO data. Instead, they cite three references: Regier et al. 1988; Wells et al. 1989; and Almeida-Filho et al. 1997. Let's check these references.

The first refers to an Epidemiological Catchment Area study of 12 month prevalence. Not lifetime. The ECA, as we've previously seen, gave a lifetime estimate of 1 in 3. The 12 month estimate is 15.4%, or 1 in 6. No 1 in 4 to be found here. The second refers to a 1989 paper from Christchurch, New Zealand. It reported a lifetime prevalence of 65.8% (sic) for any mental disorder. 2 in 3. For the "main" diagnoses, i.e. excluding most anxiety disorders, it was 36.6%. 1 in 3. The closest I could find to 1 in 4 in this study was 22.9% for main disorders, also excluding substance abuse disorders. 1 in 4, 1 in 3, or 2 in 3 - take your pick. The last reference is to a Brazilian study finding lifetime prevalence rates from 31.0% to 50.5% in three cities.

So, in 2001, the WHO quoted 1 in 4, but their only references, if taken seriously, put the lifetime prevalence is more like 1 in 2. So we still don't know where 1 in 4 comes from.

Recently, the National Comorbidity Survey Replication (NCS-R), another Kessler project, claimed a lifetime prevalence of any disorder in Americans of 50.8%. But the proportion suffering from a disorder in any one year was estimated at about one in four. So that's 1 in 4 at last, but that number appeared only appeared in 2005 - far too late to explain the origin of the meme. (And it was yearly, not lifetime, but you can see how people might have misinterpreted it.)

So, I give up. I don't believe there is a single source for 1 in 4. If anyone thinks they know where I've gone wrong, please let me know. But as far as I can see, 1 in 4 lifetime represents a kind of informal average of all of the studies I've discussed. It's a number that sticks in people's minds because it's high enough to capture the sense that "they're very common" while not being so high as to make people think "that's ridiculous" (as most of the actual estimates do). It's less a statistic, more a collective guess.

In the next post, I'll try to make sense of all these numbers.

[BPSDB]

Grant, B. (2006). About 26% of people in the US have an anxiety, mood, impulse control, or substance disorder Evidence-Based Mental Health, 9 (1), 27-27 DOI: 10.1136/ebmh.9.1.27