Biff and Dilara were having an argument over what fraction of people would likely go out of their way to drive over a live organism if it were standing innocently by the side of the road. Dilara, whose heart is pure, guessed that fewer than 2% of people would behave that badly—roughly the proportion of people who score as psychopaths in standard testing.

Biff, who isn’t revealing what he knows, guessed that the fraction would be higher, perhaps 5%. To settle the debate they analyzed data from an experiment in which a rubber facsimile of a turtle, a tarantula spider, a snake, or a leaf was placed on the paved shoulder of a two-way road (Rober 2012). Of 1000 vehicles observed to drive by, 60 swerved onto the shoulder in an effort to drive over the rubber organism. Let’s assume (perhaps unrealistically) that each vehicle represents an independent trial and that the probability of someone attempting to flatten the rubber organism is the same for each organism. Are these data consistent with a fraction of 2%? Are they consistent with a fraction of 5%?