Inside each capsule was a small sheet, to be pulled out like the slip from a fortune cookie. But these small strips did not predict the future; they changed it. Each paper’s inscription scheduled the assignment of what scientists would call a “treatment condition”—an intervention that, from that day onward, would alter the life outcomes its subjects experienced, just as a pill randomly allocated in a pharmaceutical trial might alter a participant’s health. Pirnie would not have thought of his role in these terms, but on December 1, 1969, he was serving as a lab assistant in one of the most significant randomized experiments in history: the Vietnam Selective Service Lotteries.
“The lotteries” not only changed how the Selective Service chose men for the conflict in Vietnam, they also marked a turning point in the history of science. By assigning military induction via an arbitrary factor uncorrelated with personal traits, the lotteries amounted to an experiment.