Question: When did the man dubbed  "the most influential private citizen in the America of his day" hire Elmo Roper?
Sentence (from "Elmo Roper"): His prediction of Franklin Delano Roosevelt's electoral victory over Alf Landon in 1936 was correct to within 0.9%; his 1940 prediction of Roosevelt's victory was correct to within 0.5%, further solidifying the reputation of Roper's techniques.
Relevant evidence: No