All too often we see a story in the newspaper where numbers are painfully parroted without giving any consideration to what they actually mean - and all too often that means we need recite our favourite mantra, 'correlation is not causality'. Today's paper carried a wonderful example of this, citing 'research' by Lloyds Bank showing that living in the vicinity of a supermarket will have a varying impact on the price of your house 'depending on the status of the shop.' As we all know, it shows nothing of the kind. There may be a correlation between being near the shop and house prices - but it's highly unlikely it's causal. The reason we can be reasonably sure of this is that occupant of the number 4 position, Iceland. Anyone who knows their 'status of the shop' rankings knows that Iceland is the pits - certainly below Asda. I don't doubt the pulling power of Waitrose, but the fact is I'd suggest there are other causal factors at ...

A story in the news today was a classic example of the confusion of correlation and causality. Scientists are always banging on about this, and some people wonder how this apparent statistical nicety matters - yet it's the reason that over the centuries people have been accused of witchcraft. Correlation is when two things happen in proximity - of time, space or both. Causality is when one causes the other. Because we understand the world through patterns, when there is correlation, we tend to assume causality - but without evidence, this is a mistake. In the case of witches, an old person might curse a farmer for not giving them some milk. Two days later, one of the farmer's cattle dies. Burn the witch! You might think that we are beyond such thinking in the UK, but unless there is data that wasn't presented in this news story, we clearly aren't (I read it in the i newspaper, but I'm sure it was elsewhere too.) There has been a large rise in the number of stude...

I have just read Ken Thompson's book Where Do Camels Belong for review , and it's one of those rare books that demands to be talked about. In the review I make the apparently outrageous claim that this book is to ecology what Darwin's Origin of Species is to evolution. By that I don't mean to minimise the importance of Origin - of course it's far more significant, because evolution is a much more fundamental part of biology. But just like Origin , Thompson's book points out an aspect of the science that is fundamentally obvious and crying out to be acknowledged, but that the experts of the time generally deny without even thinking about it. In the case of Camels , the topic is invasive species. We spend large amounts of money trying to control foreign plants and animals that come to our country, terrified that these aliens are taking over the habitat of our natives (is this beginning to sound like a UKIP statement?), in a panic that the natural balance will...

Thanks to the excellent Rosy Thornton for pointing out this piece in the Guardian blogs , suggesting that we should 'make sure the next book we read is by a woman.' I find this offensive and I suspect behind the rhetoric is my favourite bugbear, a confusion of correlation and causality. I would suggest that the vast majority of people do not choose their books based on the gender of the author, even subconsciously. Instead, most of us read books in a genre or genres that we like (and there's nothing wrong with that, though I always encourage people to experiment and take a tiptoe out of their habitual genres). Here comes the correlation bit. In quite a few genres, one sex of author dominates. I happen to read mostly popular science and science fiction, which have a preponderance of male authors. If instead I happened to enjoy reading fiction the genre that is usually labelled 'chick-lit' (though I think the term is going out of fashion), I suspect I would be ...

Does this get you pregnant? Sorry if that title sounds a bit like an obscure scientific paper, but there's an important point to make. I was listening last night to a radio documentary about domestic violence among military personnel and it made the most fundamental scientific blunder. It missed a phrase that should be tattooed on the hand of every broadcaster: ' Do not confuse correlation and causation .' Let me take a step back with an example that was used on my Operational Research masters course. For a good few years after the war, the pregnancy rate in the UK had a strong correlation with the import of bananas. When more bananas were imported there were more pregnancies. Fewer bananas, fewer pregnancies. The amusing response is that the bananas were causing the pregnancies. But to accept that at face value is to miss two other possibilities. One is simple reversal. The pregnancies could be causing the bananas. By this I mean that there could be a causal connec...