When the sums don’t add up

January 15th, 2004 by Ben Goldacre in bad science, scare stories, statistics | 2 Comments »

When the sums don’t add up

Ben Goldacre
Thursday January 15, 2004
The Guardian

Like most people who know the first thing about science, I don’t usually bother to read scare stories in the media, as I know they’re not going to tell me anything useful. Parabens from deodorant in breast cancer cells? That sounds interesting. Oh, you haven’t measured it in normal cells yet. Thanks for wasting my time. Four minutes poorer, life goes on.

And the stories always fit that anti-science, anti-government, anti-industry, anti-medical agenda, as if they were the same thing, with shared blame. But here’s some real news: we’re not doing so badly. In the chemical industry, red-list discharges – releases of the most noxious substances – have fallen by 95% over the past decade.

So I’ll tell you what I want to know from a scare story, or any science story. If it’s about an experiment, I want to know what the experiment was, what the results were and where it was published. That’s not so much to ask. If it’s a story about risk, based on population data, I want to know the number of people looked at and the statistical significance of the data – the figure that tells me how reliable the data is. That’s really not unfair.

Look at the crimes of scare stories. They extrapolate from speculative laboratory data pretending the population data really exists. Or they leave out key information. So this week, eight newspapers reported a possible link between pancreatic cancer and aspirin in women. Most managed to report fairly accurately that it was a study of almost 90,000 women, that those who took two 325mg tablets of aspirin a week for 20 years had a 58% increased risk of pancreatic cancer, and that in women who had taken two tablets per day, the risk increased to 86%. Although only the Times and the Daily Mail reported that the total number of cancer cases was 161 over 18 years. Crucially, only the Times made it clear the 86% increase was only associated with high consumption for at least four years.

Perhaps the public have got their heads screwed on anyway. It’s been shown that scare tactics have little long-term effect on public behaviour: that’s why all those well-intentioned lies about illegal drugs never worked. If the media are to be believed, the day after the salmon story, fish were lying unsold in the ice of Smithfield market, but less than a week later sales are back to normal, just like beef and baby milk.

It looks like the public, unconsciously, apply what those who formulate public policy informed by science call “the precautionary principle”: act cautiously, over a speculative finding, until further data fails to back it up. We stop buying salmon for a day or two on the one in a thousand chance that we’re not being misled, shrug, and get on with our lives. As Bill Hicks once said: “I’ve got news for you: non-smokers die every day.” Two thousand of you will die this year from accidents at home; 200, I’m afraid, will be assaulted and then die; 500 will be accidentally poisoned. Tie your shoelaces, check the milk, and stop looking at my bird, if I were you.


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