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The Hidden Half - Michael Blastland *****

Michael Blastland is co-author of one of my favourite titles on the use and misuse of numbers, The Tiger that Isn't - so I was excited to see this book and wasn't disappointed.

Blastland opens with the story of a parthenogenic crustacean that seems to demonstrate that, despite having near-identical nature and nurture, a collection of the animals vary hugely in size, length of life and practically every other measure. This is used to introduce us to the idea that our science deals effectively with the easy bit, the 'half' that is accessible, but that in many circumstances there is a hidden half that comprises a whole range of very small factors which collectively can have a huge impact, but which are pretty much impossible to predict or account for. (I put 'half' in inverted commas as it might be fairer to say 'part' - there's no suggestion that this is exactly 50:50.)

We go on to discover this hidden half turning up in all kinds of applications of science and maths from economics to healthcare, from the lives of individuals who were delinquent as children to measuring the benefit (or not) of giving a poor family a cow. Blastland picks out a number of factors that tend to mislead us - that as humans we aren't consistent in our responses, that things change with location and time, that the way research is undertaken can generate false results, that principles can mislead us and far more. As he points out, what this does is make us aware of the limitations of applied maths (particularly economics) and science. He is not saying we shouldn't use them - they are far better than the alternatives - but we have to be aware of their limitations.

At the end of the book, Blastland comes up with some suggestions for dealing with the hidden half. It isn't going to go away, and there are no easy solutions, but he does have some interesting ideas on mitigation. For example, he suggests we should experiment more (with political policies, for example), remember that we are betting on knowledge rather than making use of certainty and, for me, most importantly that scientists, journalists and politicians should do more to communicate the uncertainty involved. It's not that we want our politicians to be hesitant, but it would be far better if they made it clear that there are very few clear linkages between policies and outcomes. I was particularly struck by some data on GDP figures. The media and politicians often spend ages agonising over a GDP change of, say 0.2 per cent. The headline figures are revised over time as better data is available: Blastland points out that a typical correction might be 0.4 per cent up or down (and can be as high as 1 per cent). This makes it very clear that making pronouncements based on a 0.2 per cent change is futile and highly misleading.

My only criticism is that I felt that the book could have done with even more specific examples: in this kind of book, it's the examples that have the real bite and savour. Blastland spends a bit too long philosophising on the hidden half in a way that feels a little repetitive. It's not there aren't great examples (plenty more than the ones mentioned above), it was just for me that the ratio of examples to musings wasn't quite right. A brief mention also to the cover design - it's very clever (though I couldn't help thinking it had been put on wrong and wanting to re-position it).

We are getting more books now about the reality of applied maths (particularly economics) and science, which is an extremely good thing, provided the message is carried through to journalists and others who have to communicate these matters to the public. An excellent book.
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Review by Brian Clegg
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