How to Tell the Truth With Statistics
By Bryan Caplan
From Robert Gordon‘s “Everyday Life As An Intelligence Test”:
Even defense attorney Alan Dershowitz was guilty of faulty probability reasoning when he correctly pointed out that fewer than 1 in 1000 wives who are abused by their spouses, as Mrs. Simpson had been, are later killed by them… A mathematician replied to Dershowitz, using the relevant conditional probabilities, that “if a man abuses his wife and she is later murdered, the batterer is the murderer more than 80 percent of the time. [references omitted]
Since I believe in the preponderance standard of proof for all offenses*, Gordon’s factoid has some interesting implications for me. In a Caplanian world, this base rate would, by itself, have been a prima facie case against O.J. Simpson. To avoid a conviction, it would have been virtually essential for him to take the stand to explain, loud and clear, why we should believe that he was the exception that proved the rule.
* Assuming the charge ought to be an offense in the first place. I’d nullify if I thought it shouldn’t.