The return rate was 23% (which is incredibly high for a volunteer survey, often return
rates are below 5%) meaning 2.3 million ballets were returned. For reference, the US
Census counted 123 million Americans in 1930 and 132 million in 1940. Most modern Gallup
polls are based on surveys of 1,000 Americans.
The poll predicted Roosevelt would get 43% of the vote. But Roosevelt won by a
landslide getting 62% of the vote.
Why was Literary Digest so wrong? Their sample was a sample of convenience and
the sample was not representative of the target population (American adults). In short,
their sample over-represented wealthier Americans (people with phones and cars) who, even
then, tended to be Republicans.
George Gallup accurately predicted the 1936 election. He also accurately predicted the
outcome of the Literary Digest poll before the results were tabulated! He used quota sampling to select his sample which made his sampled
population much closer to his target population. This was the beginning of George Gallup's
successful career. Today the term "Gallup poll"
is familiar to most Americans.
