Quote:
...The pollsters, the committee concluded, had made many errors. All three national polls had not been alive to the possibility of a decisive swing to Truman in the last two weeks of the campaign. Gallup and Crossley stopped polling too early. Gallup's final prediction, published the day before the election, was actually based on two national samples gathered during mid-October. Crossley's final forecast was derived from a combination of state surveys taken around mid-August, mid-September and mid-October. Roper's final estimate used data he collected in August, which provided the basis for his September 9 column in which he predicted Dewey's victory and announced he was no longer going to publish periodic surveys. (Roper, however, did take a poll in the final week of the campaign, which he did not publish. It showed a slight upswing for Truman, but Dewey was still far in the lead.)...
Emphasis mine.