"What level of proof do we need about the harmfulness of some activity before we act? I decided to tell the story of a man named frederick hoffman, a remarkable man," he says. Hoffman was one of the first people to sound the alarm about smoking. But perhaps his most important work concerned what was known at the time as miners asthma. He looked at census data who was still working after the age of forty five. For farmers at the time, almost a third were still working. From miners, it was a fifth. "I think that this miner's asthmus thing is something that we should be concerned about."