Joshua Prettyman reviews ‘The Tiger That Isn’t: Seeing through a world of numbers’, by Michael Blastland and Andrew Dilnot.

This is one of the very best books I have read about the importance of being careful around numbers, written by the creators of radio 4’s More Or Less it is a fact-packed gold mine of interesting statistical nuggets that really make the reader pause to think. The book makes the analogy that the human instinct which tells us to run every time we see stripes just in case there’s a tiger applies just as strongly in the modern number-filled world. Who wouldn’t cheer the previous government for spending £300million to create new childcare places? The authors put that number into context and explain that it means roughly £1.15 per week per child; could you find childcare for £1.15 per week? The human brain is not set up for dealing with massive numbers and yet the papers are full of them, each week a story about the economy tells us that £70billion is spent here, £12trillion is owed there; slapping zeros in the headline sells papers but it is misleading. Saying, as papers in 2007 did, that the NHS had a deficit of £800million makes the institution appear to be in dire straits, saying that the NHS hit its targets to within a 1% margin makes it sound well managed, so which is correct? Both are in fact; £800million is only 1% of the NHS budget, it equates to less than the cost of one visit to our GP each! The press are looking to stir up trouble and if they want to make any government, or organisation, look bad it’s very easy to do so simply by confusing the public with large numbers. Similarly, if they wish to make someone look good, such as themselves or the political party they support, with clever reporting they can do just that and they depend on the public’s ignorance of statistics to bend our opinions.

But this book is not at all patronising, it never makes fun of the public for their shortcomings but treats the subject very maturely. The only time the authors resort to a more childish style is when it isn’t the general public but the professionals in charge who are so easily swayed by dodgy stats. There is an amusing (and rather worrying) account of a survey conducted at a conference of senior civil servants; when asked how much a family would have to earn to be placed in the top 10% of UK households some of those asked overestimated the figure by as much as five times! None got near to the true figure of £35,000 and these are the people who are in charge of taxes and benefits. Another case study involves asking 24 physicians what the chances are of a woman having breast cancer given that a test for it came back positive. The test is 90% accurate for a positive result and 93% accurate for a negative. Only 2 of the 24 got the correct answer (11%), 20 of them guessed around 90%, if you are a woman with an 11% chance of having cancer and some professional tells you that you have a 90% chance of having cancer there could clearly be a lot of unnecessary grief caused.

Like myself, I suspect that the authors wish to see a greater level of mathematical competency across all professions and in general, but this isn’t the message given by their book. Instead they merely call for us all to be more wary of big numbers and baffling percentages in the media, they constantly praise the good work of statisticians throughout and blame bad reporters and journalists for twisting the figures to fit their ideals. I was surprised how much I learned (as a mathematician I presumed I would encounter nothing new here) but the day after I finished the book I was told by the BBC news that drinking can increase a woman’s risk of cancer by as much as 20%! Oh my god, my own mother is on death row, 20% is a huge number, the women in my life are doomed (except my wife; she doesn’t drink). Or at least that’s what I might once have thought, but having read the tiger that isn’t I know better than that; the BBC will always tell you how much the risk is raised by but they never tell you what the risk actually is. Say the risk of any given woman getting cancer is 0.5%, a 20% increase means that this is raised from 0.5% to 0.6%; not so scary now, eh? But a number like 0.6% won’t grab the headlines, 20% will. This kind of alarmist reporting is everywhere, from the Daily Mail and the BBC to the Guardian and the Independent, journalists are shocking and caution is required at all times; a big number such as £800billion might look like a scary tiger but it’s often just grass waving in the wind and whenever this happens there is a reporter waiting to convince us that it really is a tiger and maybe make some money out of our panic.

I promise that you will look at the world differently after this book, if everybody reads it we might finally stop running from imaginary tigers and start dealing with numbers sensibly.

Joshua Prettyman is studying Maths at the University of Edinburgh but he has a massive passion for natural history and wildlife as well as all things scientific.