Ah yes, Dr Cliff Arnall's equation for the most depressing day of the year - the third Monday in January. This started life as a corporate puff for Sky Travel (end of January, perfect time to book a holiday). But now Blue Monday has slipped out of Sky's ownership and become part of the canon of pseudoscientific media myth.
Most alarmingly, last year it was used by the Samaritans, and this year by the Mental Health Foundation. These people, apparently, think it's okay to use bullshit to promote awareness of mental health issues.
The Sun said: "It is officially the most depressing point of the year. The misery of Blue Monday was worked out by psychologist Dr Cliff Arnall." The Express loved it. The Mirror too. "Experts have worked it out," said Channel 4. CBBC fed it to children: "Researchers say the third Monday in January is when people are more unhappy than at any other time."
When I last criticised Arnall in 2006 (he also has a formula sponsored by Walls for the happiest day, which is in June), Cardiff University asked us to point out that he had only been a part-time tutor and had left. These efforts to distance themselves felt disingenuous since they were also, at the same time, quoting Arnall's ridiculous appearances in their monthly roundups.
I hope they are disabusing everyone else this year, including the Daily Mail, of course: "Today - January 19, 2009 - is the most depressing day in HISTORY."
Meanwhile Martin Hird, a senior lecturer in mental health and psychological therapies at Leeds Metropolitan University, told the Telegraph: "I would guess there is something in it based on the daylight hours and people's social circumstances." Right. You'd guess.
And is there good evidence? Seasonal affective disorder is its own separate thing. If you look at the evidence on the population's mood, depression, and suicide changing over the seasons, you do, in fact, find a glorious mess.
Back in 1838 Esquirol commented on the higher incidence of suicide in spring and early summer. Swinscow showed the same thing with all UK suicides from 1921-1948. So that's not winter blues.
What about elsewhere? A 1974 study on all suicides in North Carolina (3,672) showed no seasonal variation. A 1976 Ontario study found peaks of suicide and admissions for depression in spring and autumn. Suicide is highest in summer, says a paper from Australia in 2003.
Maybe you want data from the general population on mood. A study in 1986 looked at 806 males from Finland and found low mood more common in the summer. Some studies do find higher rates of depressive symptoms in the winter but some find the opposite results, like a peak in the spring (Nayham et al 1994) or summer (Ozaki et al 1995).
I'm not claiming to have done a thorough review. I'm just saying it's possibly a bit more complicated than everyone getting depressed in winter. Making up stupid stuff about the most depressing day of the year doesn't help anyone, because bullshit presented as fact is simply disempowering.
Please send your bad science to bad.science@theguardian.com