What did the selected poll say?
The published Digest returns included 972,897 Roosevelt responses and 1,293,669 Landon responses. Among those two candidates, our normalized shares are 42.9% and 57.1%. On the same two-candidate basis, the poll margin was R +14.2 and the recorded outcome margin was D +24.9: a 39.1-point difference.
What actually happened?
The original published Digest count favored Landon; Roosevelt won decisively. Normalizing both to two-party shares puts their comparison on the same denominator.
Why might the poll have missed?
Historical reanalyses identify selective participation and coverage differences. The familiar explanation that telephone and automobile ownership alone caused the miss is incomplete. Evidence status: supported, contribution uncertain.
What has not been established?
The familiar story that access to a telephone or automobile alone explains the failure is too simple. Coverage and the decision to return a form both matter. Historical reanalysis does not make the voluntary sample representative after the fact.
How should we use this example?
Gallup’s separate final estimate put Roosevelt at 55.7 and Landon at 44.3. It identified the popular-vote winner while still understating Roosevelt’s eventual two-candidate margin. That contrast demonstrates why representative selection matters and why a correct winner call is not perfect accuracy.
Both sides are normalized to Roosevelt + Landon = 100%. Third parties are excluded from both denominators. The poll uses published voluntary response counts, not a probability sample. The historical outcome compilation can differ slightly across editions.
What to carry forward
A huge voluntary return cannot guarantee a representative sample.