In this political season, it’s useful to brush up on rhetorical skills, particularly ones involving numbers and statistics, or what John Allen Paulos called numeracy. Professor David Spiegelhalter has written a guide to some of these tricks. Read the whole thing. Highlights, though, of devices used to produce statistics which aren’t-quite-right (that is, wrong):
- Use a real number, but change its meaning
- Make the number look big (but not too big)
- Casually imply causation from correlation
- Choose your definitions carefully
- Use total numbers rather than proportions (or whichever way suits your argument)
- Don’t provide any relevant context
- Exaggerate the importance of a possibly illusory change
- Prematurely announce the success of a policy initiative using unofficial selected data
- If all else fails, just make the numbers up.
David Spiegelhalter is the Winton Professor of the Public Understanding of Risk at the University of Cambridge and president elect of the Royal Statistical Society. Among many other things, he’s an advocate for expressing life risks as micromorts.