What do a government department, a charity, a Royal College and a journal paper all have in common?
They've all quoted the same, widely used statistic: one in four people have experienced a mental health problem. And they've all sourced the figure to the same place: the 2007 Adult Psychiatric Morbidity Survey.
Except they don't all say the same thing:
Department of Health: "At least one in four of us will experience a mental health problem at some point in our life"
Mental Health Foundation: "1 in 4 people will experience some kind of mental health problem in the course of a year"
Royal College of Psychiatrists: "Almost one in four British adults ... experience a diagnosable mental health problem at any given time."
In the British Medical Journal: "In 2007 the annual psychiatric morbidity survey (APMS) estimated a UK prevalence of 23% in the past week"
We spoke to the authors of the 2007 study to find out why there might be such stark differences in interpretation.
The study itself is explicit about one of its main findings:
"in 2007 nearly one person in four (23.0 per cent) in England had at least one psychiatric disorder and 7.2 per cent had two or more disorders"
In terms of this particular survey, that means about one in four adults met the criteria or screened positive for at least one of the psychiatric conditions or behaviours being studied. That includes, for instance: forms of anxiety, depression, phobias, eating disorders and drug or alcohol dependence.
The problem, as one of the authors informed us, is putting a time period on the figure. That's because not all the conditions being measured cover the same timeframe.
Anxiety and depression, for instance, were measured by identifying symptoms people demonstrated in the past week. Alcohol dependence refers to the past six months. Meanwhile drug dependence and eating disorders were measured based on the past year.
None, however, measured prevalence over a lifetime (the study did cover lifetime prevalence for some behaviours, but not for the purposes of this particular comparison).
So while the study pinpointed one in four having had a mental health problem, it confuses matters to assign a single time period to the claim, unless looking at a specific condition within.
An old relic
That said, the one in four claim also predates the 2007 Survey, so not all references to the figure necessarily refer to the recent findings. The earliest such reference we've found is research paper dating back to 1980 by David Goldberg and Peter Huxley.
It gathered evidence suggesting that around 25% of people in 'community' samples (outside the care system at GP practices and hospitals) had some form of mental disorder in the past year. But importantly, this defined mental problems differently - excluding drug and alcohol dependence and more severe conditions such as schizophrenia.
Again, there was no measure of how many people had ever experienced a mental problem, and the authors themselves commented only a few years ago that looking at lifetime prevalence was:
"a highly questionable concept where common mental disorders are concerned, since it assumes that people not only can, but will reveal information about minor disorders that occurred many years ago, but that they have either forgotten or suppressed. For this reason, we have never quoted figures for life-time rates.
"However, for those that like to think in these terms, we would suggest that the figure of "at least 25%" is almost certainly a conservative figure."
Isn't it nice to have the whole picture?
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