1. Literary Digest Poll 1936 election: Franklin Delano Roosevelt vs. Alf Landon Literary Digest had called the election since 1916 Sample size: 2.4 million! Prediction: Roosevelt 43% Actual: Roosevelt: 62% (Literary Digest went bankrupt soon after)

2. What went wrong? Context –9 million unemployed; real income down 1/3 –Landon: “Cut spending” versus Roosevelt: “Balance peoples’ budgets before government’s budget Polling –Survey sent out to 10 million people from subscription list, telephone directories, club membership lists –2.4 million responded

3. Sources of bias Sampling frame not representative –Biased toward better off groups (and more Republican) Voluntary response bias –The anti-Roosevelt forces were angry--- and had a higher response rate!

4. Roosevelt’s percentage –Actual election result: 62% –Literary Digest prediction:43% –Gallup’s prediction of the Digest prediction (based on sample of 2,000)44% –Gallup’s prediction of the election result (based on sample of 50,000)56% Gallup used Random sampling George Gallup did it right

5. The Year the Polls Elected Dewey 1948: Harry Truman (Dem) vs. Thomas Dewey (Rep) All major polls predicted Dewey would win by 5 percentage points (even Gallup)

6. What went wrong? Quota Sampling Each interviewer assigned a fixed quota of subjects in certain categories (race, sex, age) In each category, interviewers free to choose Left room for human choice---and inevitable bias Republicans were easier to reach –Had telephones, permanent addresses, “nicer” neighborhoods Quota sampling abandoned for Random Sampling