3 Comments »Posted on Monday 19 January 2009 at 1:46 pm by Jacob Aron
In Getting It Wrong, Mathematics

According to the Daily Mail, today is “the most depressing day in HISTORY” – so say the “experts”. Forget your credit crunches, terrorist attacks and military invasions, today is Blue Monday, so we should all apparently feel very sorry for ourselves. Well, I’m quite pleased actually because I get another nonsense formula to bash!

You may remember “worst day ever” stories from years past, because in fact this little gem is rolled out annually. It is supposedly derived from a formula thought up by Cliff Arnall, “formerly of Cardiff University”, but is actually a product of PR company Porter Novelli according to good ol’ Ben Goldacre. The company approached Arnall to put his name to the “research” that was put out as part of a promotion for Sky Travel. Arnall, who Cardiff University have made clear was only a former part-time tutor for them, now seems to make a habit of promoting this rubbish at every opportunity.

On to the formula. The official “Beat Blue Monday” website offers the following formula for calculating the worst day of the year:

The model was broken down using six immediately identifiable factors; weather (W), debt (d), time since Christmas (T), time since failing our new year’s resolutions (Q), low motivational levels (M) and the feeling of a need to take action (Na).

These “immediately identifiable factors” are of course nothing of the sort; notice as well that the variable D is undefined. My usual complaints apply: variables that make no sense (how to you turn “weather” in to a number?) and broken equations (if your motivational level is zero, then the result is infinite), but there is also some nasty abuse of notation here. Na is obviously meant to stand for “need action”, but variables represented like this would normally be part of a series, e.g. Na, Nb, Nc, etc. I guess using the notation in this way makes it look more “scientific”.

Another fault is that although the formula supposedly results in a universal “worst day”, the variables seem to be very individual. Surely “time since failing our new year’s resolutions (Q), low motivational levels (M) and the feeling of a need to take action (Na)” all change from person to person? I was going to try and work back from the result to determine just what they are inputting for the equation, but it’s such a mess it isn’t even worth bothering. Today isn’t Blue Monday at all – I’ve just had a rather good laugh.


  1. 3 Comments

  2. Interesting you should say that variables like Na would normally be part of a series as we used to use the notation NA (apologies for lack of subscript!) to represent Avogadro’s Number in Physics calculations – obviously we weren’t being mathematically rigorous either!

    By Chloé on Tuesday 20 January, 2009 at 9:28 am

  3. Ah but in that case the point is to distinguish NA from any other N, for example if there are N atoms in a bar of gold, how many moles are there? N/NA.

    My choice of the word “series” is perhaps not the best, what I really mean is that Na is an unnecessary embellishment because there is only one N.

    It’s not really a question of mathematical rigour, more one of using unambiguous notation!

    By Jacob Aron on Tuesday 20 January, 2009 at 9:38 am

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