What did the selected poll say?
Gallup’s selected estimate put Jimmy Carter at 44.0% and Ronald Reagan at 47.0%. On the chart’s stated basis, that was R +3.0. The corresponding recorded outcome margin was R +9.7, for a 6.7-point difference in the margin.
What actually happened?
Gallup's final estimate put Reagan ahead 47–44. The result was approximately 51–41, a much wider win.
Why might the poll have missed?
Gallup's retrospective traces movement toward Reagan after the October 28 debate and discusses the Iran hostage crisis. This is evidence of changing measured preferences, not an identified causal effect of the debate. Evidence status: pollster interpretation.
Fenwick and colleagues studied how to allocate undecided respondents in 1980 presidential polls and validated their method with a post-election follow-up. The verified abstract does not establish why this particular final Gallup estimate missed. Evidence status: methodological context; abstract verified.
What has not been established?
A measured movement after a debate does not prove the debate caused every changed vote. The comparison cannot identify which respondents later changed preferences or who ultimately turned out.
How should we use this example?
Report the point estimate, uncertainty, timing and numerical miss together. Label this a missed margin with a correct leader, rather than turning it into a false claim that the final Gallup poll picked Carter.
One Gallup final allocated estimate is compared with all-vote election shares. Carter and Reagan do not sum to 100% in either set of reported shares. The raw D−R margin is used, without two-party normalization.
What to carry forward
Calling the winner correctly can conceal a substantial error in the victory margin.