The third Monday in January is supposedly "the most depressing day of the year". Here's what the web has to say about "Blue Monday", with help from Microsoft's search engine Bing.
Commuters walking through the rain(PA)

PA

You might have seen or heard mention that today, 17 January 2011, is "Blue Monday": the most depressing day of the year.

You won't be that surprised to learn there is no scientific basis for this description.

The name was first popularised in 2005 as part of a publicity campaign devised by the now defunct satellite channel Sky Travel.

The campaign claimed that the third Monday in January was the most depressing day in the calendar year.
The depression "equation"

This assumption was supported by a press release containing a mathematical equation published under the name of Cliff Arnall, who at the time was a tutor at the Centre for Lifelong Learning, a further education centre affiliated with Cardiff University.

The "equation" ran as follows:
[W + (D-d) x Tq]
______________
M x Na
where W = weather, d = Debt, T = time since Christmas, Q = time since failing our new year resolutions, M = low motivational levels and Na the feeling of a need to take action.
D was never defined in the press release, nor were any of the equation's units.
"Corrosive, meaningless, empty, bogus nonsense"

Shortly before "Blue Monday" in 2007, Dr Ben Goldacre wrote in the Guardian of how this equation was "scientifically uninformative, and driven by money."

According to the Goldacre, the "Blue Monday" press release was substantially pre-written by PR agency Porter Novelli, which had then offered academics money to put their names to it.

Indeed, the Guardian later printed a statement from Cardiff University distancing themselves from Cliff Arnall: "Cardiff University has asked us to point out that Cliff Arnall... was a former part-time tutor at the university but left in February."

Goldacre concluded: "I am of the opinion that these equation stories - which appear with phenomenal frequency, and make up a significant proportion of the total science coverage in the UK - are corrosive, meaningless, empty, bogus nonsense that serve only to caricature and undermine science."
Other appearances of 'Blue Monday'

Despite Goldacre's efforts, the "Blue Monday" tag has persisted and has even been taken up by other organisations such as the Mental Health Foundation.

This year the phrase has given rise to a website, beatbluemonday.org, which confusingly labels the fourth rather than the third Monday of the month as "Blue Monday".

The website declares that Blue Monday is "the brainchild of Flexible Thinking Forum, a creativity consultancy which helps managers challenge their thinking to come up with new ideas and new ways of doing things."
The site also references Cliff Arnall, but describes him as a "happiness and motivation expert" and "formerly a researcher, lecturer, and post graduate tutor at the Medical and Dental School of Cardiff University."
Such initiatives only partly hint at the less flippant side to the dubious concept of "Blue Monday".

Raising awareness of mental health issues and helping to fight depression are serious topics that merit serious attention and resources. MSN Him has

By contrast, another website treats the idea of "Blue Monday" as a hook upon which to hang a good-natured campaign promoting the simple notion of cheering people up. But importantly, this site does not pretend the concept of "Blue Monday" has any grounding in fact or science.

No scientific formula for feeling blue
In short, there's no scientific or mathematical reason at all that you might be feeling a little blue today. But if you are, here are a few things that might constitute something of a pick-me-up.

Opera North begin their winter season in Leeds today with a new production of Bizet's opera Carmen, while Lenny Henry begins previews for his new musical stand-up tour at the Corn Exchange in Newbury.

The Australian Open is now underway, giving Andy Murray the chance to get his year off to a winning start. The Brit Insurance Designs of the Year shortlist is being announced. And Tom Jones is performing his latest album Praise and Blame as part of the Celtic Connections festival in Glasgow.