I served on an Ad Hoc Committee of the American Association for Public Opinion Research that was formed in response to the controversy over the public polls in the New Hampshire Democratic primary. The Committee’s report was released today. Michael Traugott of the University of Michigan chaired the committee, and did yeoman’s work keeping the process going.
There were four factors the Committee found (out of a significant number examined) that could have contributed to the polls uniformly predicting (wrongly) an Obama win in the NH Dem primary. From the AAPOR press release:
- Given the compressed caucus and primary calendar, polls conducted before the New Hampshire primary may have ended too early to capture late shifts in the electorate’s preferences there.
- Most commercial polling firms conducted interviews on the first or second call, but respondents who required more effort to contact were more likely to support Senator Clinton. Instead of continuing to call their initial samples to reach these hard‐to‐contact people, pollsters typically added new households to the sample, skewing the results toward the opinions of those who were easy to reach on the phone, and who more typically supported Senator Obama.
- Non‐response patterns, identified by comparing characteristics of the pre‐election samples with the exit poll samples, suggest that some groups who supported Senator Clinton–such as union members and those with less education–were under‐ represented in pre‐election polls, possibly because they were more difficult to reach.
- Variations in likely voter models could explain some of the estimation problems in individual polls. Application of the Gallup likely voter larger error than was present in the unadjusted data. The influx of first-time voters may have had adverse effects on likely voter models.
It is important to point out — as the report does — that outside of the NH Dem primary, both primary and general election polling were on target this election cycle. However, it is worth reviewing and assessing the controversy. Pollsters continually need to reevaluate their methodologies and challenges, particularly in a world where so much is changing.
Our friend Mark Blumenthal, at the second best polling blog — pollster.com 😉 — wrote up a blog post well worth reading. Mark has some good links to other posts about the NH issues.