Required Reading: Statistics and Inferences

In a blog post on the New York Times‘ site today, Nate Silver raises cautions about the use of statistical evidence in an argument that could be very useful to us. He’s discussing the debate before the Supreme Court right now regarding the Voting Rights Act, which is far afield of our recent class discussions. But his warnings about what conclusions we reach based on statistics are very relevant, including his point that “the act of citing statistical factoids is not the same thing as drawing sound inferences from them” (¶4). Silver’s example, from late in the piece:

Most of you will spot the logical fallacy in the following claim:

No aircraft departing from a United States airport has been hijacked since the Sept. 11 attacks, when stricter security standards were implemented. Therefore, the stricter security is unnecessary.

As much as I might want to be sympathetic to this claim (I fly a lot and am wary of the “security theater” at American airports), it ought not to be very convincing as a logical proposition. The lack of hijackings were in part a product of an environment in which airport security was quite strict, and says little about what would happen if these countermeasures were removed. The same data might just as easily be cited as evidence that the extra security had been effective:

No aircraft departing from a United States airport has been hijacked since the Sept. 11 attacks, when stricter security standards were implemented. Therefore, the stricter security is working.

Go read the whole thing.

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