What caused the classic polling disaster?

The Literary Digest’s prediction that Republican Alf Landon would beat the incumbent Democratic president Franklin Delano Roosevelt in a landslide in 1936 rates as arguably the biggest disaster of opinion polling. Rather than a landslide for Landon instead Roosevelt earned a rather comfortable win. It didn’t just get the winner wrong, the poll was stunningly inaccurate. “…the Literary Digest poll gained an infamous place in the history of survey research” (Squire, 1988, 125).

The conventional explanation is one of sampling. I have seen this explanation before and may even have mentioned it in a class. The Digest sent ballots out to people it found on lists of telephone and automobile owners. These, in 1936, could be expected to be rich and skew Republican. Rather than scientifically sample the Digest had assumed that having large numbers of people responding would make up for the fact that they mostly sent the ballots to richer people. This was definitely a problem. A follow up survey showed that Landon supporters were more likely to have received a ballot than Roosevelt supporters.

Peverill Squire looked into the follow up survey more and noted that, while sampling was a problem, it wasn’t the whole problem. “..if all of those who were polled had responded, the magazine would have, at least, correctly predicted Roosevelt the winner” (Squire, 1988, 125). Those that were polled were more pro-Landon than the general public but they still had a slight Roosevelt preference. If all had responded the poll would have predicted the result of a narrow Roosevelt win.

An additional problem came from non-response bias. There was a marked tendency for Landon supporters to return their ballots at a higher frequency than Roosevelt supporters. “…the 1936 Literary Digest poll failed to project the correct vote percentages or even the right winner not simply because of its initial sample, but also because of a low response rate combined with a nonresponse bias” (Squire, 1988, 131).

Basically it had a bunch of problems not just the one we always hear about. It is a salutary lesson on how we can get our understanding of the world wrong if we don’t know what we are doing. I’m not sure why Democrats seemed so shy about admitting to supporting Roosevelt in 1936 but their reticence made the Literary Digest look pretty silly.

Read: Peverill Squire (1988) Why the 1936 Literary Digest Poll Failed, Public Opinion Quarterly, 52, 125-133