The classic example was a massive effort by the Literary Digest to forecast the Presidential election of 1936. More than 10,000,000 ballots were sent out. Something like 2,367,523 came back, mostly marked for Alf Landon. The poll predicted 370 electoral votes for the Republican candidate, and 161 for Franklin Delano Roosevelt, the Democrat. In the real election, Roosevelt won 523 electoral votes, with Landon receiving eight. What went wrong? The Digest, it seems, sent ballots to addresses collected from the subscription lists of magazines, and also from telephone directories and automobile registration lists. But magazines, telephones and automobiles were not randomly distributed among the American population in 1936.

Ruggero J. Aldisert, Agatha D. Aldisert, Logic for Lawyers- A Guide …, loc. 1109