“One in four” with a mental health problem: the anatomy of a statisticBMJ 2012; 344 doi: http://dx.doi.org/10.1136/bmj.e1302 (Published 22 February 2012) Cite this as: BMJ 2012;344:e1302
- Stephen Ginn, Roger Robinson editorial registrar, BMJ,
- Jamie Horder, postdoctoral neuroscientist researcher, Department of Psychiatry, University of Oxford
“It’s time to talk” is a campaign currently being promoted by Time to Change, a charity whose aim is to change attitudes to people with mental ill health. On the charity’s website a banner tells us: “1 in 4 of us will experience a mental health problem at some point in our lives, but we still don’t talk about it. What are we afraid of?”
Yet it is not always clear to what the figure refers. Time to Change seems to be referring to lifetime prevalence, while a 2010 advertising campaign by Islington Primary Care Trust stated, “One in four people will experience mental health problems each year.” A statement on the Royal College of Psychiatrists’ website reads, “One in four people has a mental health problem,” implying point prevalence.
The evidence base
The number’s origin is unclear. When one of us (SG) contacted a selection of organisations that use “one in four” in their literature, they cited a number of different sources. The earliest seems to be a 2001 World Health Organization report, Mental Health: New Understanding New Hope, which stated, “During their entire lifetime, more than 25% of individuals develop one or more mental or behavioural disorders (Regier et al 1988; Wells et al 1989; Almeida-Filho et al 1997).”3
However, none of the three papers cited contains an estimate of 25% lifetime risk. One did not report on lifetime prevalence at all,4 and the two that did provide a lifetime figure of rather more than 25% (66% for “all [mental] disorders” in New Zealand and 31-51% in Brazil).5 6
Lifetime prevalence of mental disorder seems never to have been estimated in the United Kingdom. In 2007 the annual psychiatric morbidity survey (APMS) estimated a UK prevalence of 23% in the past week.7 In numerous other countries lifetime estimates are reported as being in the region of 50%.8
We are unaware of any evidence that straightforwardly supports a UK lifetime prevalence of 25%. The APMS past week prevalence most robustly supports one in four as a statement of the UK’s 12 month prevalence,7 but in this case the UK lifetime prevalence would be expected to be much higher.
A 2005 meta-analysis estimated a yearly prevalence of 27% for the European Union (including the UK),9 but a 2010 update of this work revised this to 38% a year,10 as a result of including more disorders such as insomnia and attention-deficit/hyperactivity disorder. This highlights the fact that over the years the consensus on what constitutes mental disorder has often changed.
Different population surveys adopt different definitions, and there is no agreement about whether to treat, for example, a phobia such as arachnophobia as “mental illness.” No major study has considered nicotine dependence or male erectile disorder in their calculations, despite these disorders being widespread and listed in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV). Nicotine dependence is perhaps responsible for more deaths than any other psychiatric disorder.
Furthermore, surveys such as the APMS establish diagnosis in a very different way from how it is discerned clinically. In the clinic, a doctor works from a patient’s presenting complaint, through their history, and on to mental state examination. By contrast the APMS recruited a large representative sample and used a structured diagnostic interview to screen each participant for a range of disorders. Structured interviews involve a patient answering a fixed series of questions taken from published criteria.
Systematic checking of a symptom inventory in this way lacks the benefit of clinical judgment and simultaneously creates a risk of both over-diagnosis and under-diagnosis. Taken literally, the DSM-IV criteria for major depressive disorder would deem many people depressed after bereavement or the end of a relationship. Conversely, a patient’s imperfect recall or lack of insight into their own psychopathology could lead to under-reporting.
The popularity of “one in four”
Despite these drawbacks, why has this figure proved so popular? We would like to suggest some reasons.
Demonstrating relevance: For journalists, quoting a high prevalence of mental disorder helps illustrate the newsworthiness of stories about mental health.
Fighting stigma: The one in four statistic has been used extensively by charities to advocate the interests of people with mental illness. Much of their recent campaigning has focused on attempting to combat stigma and prejudice through providing a more inclusive vision of mental disorder—one in which it is nothing unusual and a threat to everyone.
Not too big, not too small: If the intent is to raise awareness of the burden of mental illness, why do organisations not cite the even higher, and better supported, figures of one in three or one in two lifetime prevalence? We suggest that one in four is high enough to gain people’s attention but not so high that it provokes incredulity, as claims that over 50% of people have had a mental illness indeed have.
The one in four figure for mental illness prevalence is widely quoted, related variously to lifetime, yearly, or point prevalence. The evidence indicates that it is best supported as an estimate of yearly prevalence. However, estimates of the population prevalence of mental disorder should be approached with caution, as the methods used often have shortcomings. It is important that people know that mental illness is common and that treatment of mental disorder is essential, but it is not clear that championing a poorly supported prevalence figure is the way to achieve this.
Cite this as: BMJ 2012;344:e1302