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Sunday, October 11, 2009

Statistically

"Statistically, airplane travel is safer than driving..." "Statistically, you're more likely to be struck by lightning than to..." "Statistically, the benefits outweigh the risks..."

What does statistically mean in sentences like this? Strictly speaking, nothing at all. If airplane travel is safer than driving, then that's just a fact. (It is true on an hour-by-hour basis). There's no statistically about it. A fact can't be somehow statistically true, but not really true. Indeed, if anything, it's the opposite: if there are statistics proving something, it's more likely to be true than if there aren't any.

But we often treat the word statistically as a qualifier, something than makes a statement less than really true. This is because psychologically, statistical truth is often different to, and less real than, other kinds of truth. As everyone knows, Joseph Stalin said that one death is a tragedy, but a million deaths is a statistic. Actually, Stalin didn't say that, but it's true. And if someone has a fear of flying, then all the statistics in the world probably won't change that. Emotions are innumerate.

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Another reason why statistics feel less than real is that, by their very nature, they sometimes seem to conflict with everyday life. Statistics show that regular smoking, for example, greatly raises your risk of suffering from lung cancer, emphysema, heart disease and other serious illnesses. But it doesn't guarantee that you will get any of them, the risk is not 100%, so there will always be people who smoke a pack a day for fifty years and suffer no ill effects.

In fact, this is exactly what the statistics predict, but you still hear people referring to their grandfather who smoked like a chimney and lived to 95, as if this somehow cast doubt on the statistics. Statistically, global temperatures are rising, which predicts that some places will be unusually cold (although more will be unusually warm), but people still think that the fact that it's a bit chilly this year casts doubt on the fact of global warming.

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Some people admit that they "don't believe in statistics". And even if we don't go that far, we're often a little skeptical. There are lies, damn lies, and statistics, we say. Someone wrote a book called How To Lie With Statistics. Few of us have read it, but we've all heard of it.

Sometimes, this is no more than an excuse to ignore evidence we don't like. It's not about all statistics, just the inconvenient ones. But there's also, I think, a genuine distrust of statistics per se. Partially, this reflects distrust towards the government and "officialdom", because most statistics nowadays come from official sources. But it's also because psychologically, statistical truth is just less real than other kinds of truth, as mentioned above.

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I hope it's clear that I do believe in statistics, and so should you, all of them, all the time, unless there is a good reason to doubt a particular one. I've previously written about my doubts concerning mental health statistics, because there are specific reasons to think that these are flawed.

But in general, statistics are the best way we have of knowing important stuff. It is indeed possible to lie with statistics, but it's much easier to lie without them: there are more people in France than in China. Most people live to be at least 110 years old. Africa is richer than Europe. Those are not true. But statistics are how we know that.

[BPSDB]

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