Highway Fatalities and Mexican Lemons

A reminder that correlation does not imply causality:

Derek Lowe of Corante’s ‘In the Pipeline’ (a drug-discovery blog) points to this graph in an article by Bristol-Myers Squibb’s Stephen Johnson, titled, The Trouble with QSAR (OR How I Stopped Worrying and Embrace Fallacy).

Lowe writes, ‘The most arresting part of the article is the graph found in its abstract. No mention is made of it in the text, but none has to be. It’s a plot of the US highway fatality rate versus the tonnage of fresh lemons imported from Mexico, and I have to say, it’s a pretty darn straight line. I’ve seen a lot shakier plots used to justify some sweeping conclusions, and if those were justified, well, then I’m forced to conclude that Mexican lemons have improved highway safety a great deal. The vitamin C, maybe? The fragrance? Bioflavanoids?

‘None of the above, of course. Correlation, tiresomely, once again refuses to imply causation, even when you ask it nicely.’

If only more people (especially policy makers) would learn this lesson…