By May 1, 1948, 156 interviews had come in. And as Doll and Hill sifted through the preliminary batch of responses, only one solid and indisputable statistical association with lung cancer leapt out: cigarette smoking. As more interviews poured in week after week, the statistical association strengthened. Even Doll, who had personally favored road-tar exposure as the cause of lung cancer, could no longer argue with his own data. In the middle of the survey, sufficiently alarmed, he gave up smoking.
