Sharks rampage in Australia. Let’s bring in a statistician.

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All day long the top story on Time.com has been this one about a spike in shark attacks in Australia. It starts:

Swimmers at Australian beaches are usually reassured by statistics that indicate they are more likely to be struck by lightning than chomped by a shark. But after three non-fatal shark attacks in the country in less than 48 hours and a deadly one last month, some are wondering if the odds have changed — and whether Australia’s efforts to protect sharks are to blame.

As a member of the mainstream media that brought you the Summer of the Shark, I’m a little sensitive to shark-attack hype. Rory Callinan, our man down under, does a really good job deflating the notion that sharks are suddenly out to get us and we need to go kill them.

In an effort to help him out, and reproduce a cool chart I saw in this book, I’d like to mention a study of smoking in Montana that was published in the British Medical Journal a few years ago. The city of Helena had a 6-month smoking ban, during which the number of people showing up to the local hospital because of a heart attack fell by 40 percent. When the ban ended, the number went back up. Cause meets effect? It’s tempting.

But here’s the chart:

heartattacks1

Those little asterisks signify years when the number of heart-attack deaths varied by around 30 or 40 percent. I know the data doesn’t line up perfectly with hospital admissions, but still it’s the sort of thing we might want to consider before we go shark hunting in Australia. Sometimes a data blip is just a blip.

Barbara!

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