At the time the weekly magazine Literary Digest was the leader in electoral predictions -- the Nate Silver of its day, if you will. In advance of the 1936 election, Literary Digest mailed out some 10 million postcard "ballots" to a list assembled from rosters of different clubs and associations, voter registration rolls, city directories, and -- crucially -- telephone directories and lists of registered car owners. Those latter two groups made up the bulk of the list. Days before the election, the Digest predicted a 3-to-2 victory for Landon. When Election Day came, Roosevelt won one of the most decisive victories in the 20th century, carrying 46 of 48 states and winning 62 percent of the popular vote.
Was the telephone and automobile distribution at the heart of the error? That's the conventional story, "a staple of statistical literature," as Maurice C. Bryson called it in an The American Statistician in 1976. A 1974 statistics book by Robert Reichard, The Figure Finaglers, made that case:
The time was late 1935.* The opinion ostensibly being measured: the voter's choice for the president -- the incumbent, President Roosevelt, or the challenger, Senator Alfred M. Landon of Kansas. Everything was planned impeccably -- with a statistically significant number of voters to be called up from all sections of the country. But the planners forgot one basic fact: the use of the phone itself was introducing a bias into the sample. Remember, this was 1935, and the people who owned phones at that time did not representa cross section of the American public. Quite the contrary. Telephones were a luxury then -- and the people being sampled were the relatively affluent ones -- and hence the ones more likely to vote for the Republican candidate.
There's just one problem with this explanation and others that echoed it. As Bryson noted, "The are all wrong!" He wrote:
Good statisticians should have cauth the mistake, since the telephone-survey excuse is inherently implausible. ... Since voter participation tends to be highest among the well-to-do, the telephone owners shouldn't have been all that bad as a sample of the voting population. Furthermore, consider quantitatively the Digest's prediction that Landon would get about 60 percent of the vote. If he had obtained 60 percent of the votes of all those with telephones, then -- assuming two voters per phone -- he would have had a block of over 14 million votes, out of the mere 16 million he actually got. That would leave Roosevelt carrying the non-phone voting population by an incredible 27-to-2 million vote margin. If this were not already implausible enough, one could note that Landon won heavily only in the (non-Southern) rural areas of the country, where telephones were relatively scarce. In such a well-to-do area as Westchester County, New York, presumably well-populated by phone owners, the Landon margin was a modest 51 percent.
For its part, Literary Digest felt the same way. In its own assessment, released the week after the election, the error was not the result of the Digest's failure to "reach the lower strata." Its editors explained:
[But] the "have-nots" did not re-elect Mr. Roosevelt. ... As Dorothy Thompson remarked in the New York Herald Tribune, you could eliminate the straight labor vote, the relief vote, and the Negro vote, and still Mr. Roosevelt would have a majority. ... Besides -- we did reach these so-called 'have-not' strata. In the city of Chicago, for example, we polled every third registered voter. In the city of Scranton, Pennsylvania, likewise other cities, we polled every registered voter. ... The fact is that we were as badly off there as we were on the national total. ... All this conjecture about our 'not reaching certain strata' simply will not hold water.
More recent analyses agree. A study by Dominic Lusinchi published this past spring in Social Science History applies contemporary statistical techniques to the Literary Digest data, combining it -- powerfully -- with a dataset collected by Gallup the following year (earlier analyzed by Peverill Squire in a landmark 1988 paper on the case), which sought to examine the validity of mail-ballot polls. It asked respondents whom they had voted for, whether they had received the Literary Digest ballot, whether they had returned it, and whether they had changed their minds between filling it out and voting. "The Digest's original list was no impediment to predict [sic] the correct winner. ... Had everybody on the original Digest list returned his or her straw ballot, the magazine would have been in a position to forecast the correct winner of the election: Roosevelt," Lusinchi writes.