The bends are caused by rapid changes in air pressure, resulting in the for-

mation of nitrogen bubbles in the blood. The symptoms are acute pain, and sometimes paralysis leading to death. In World War II, pilots got the bends during certain battle maneuvers. It was feasible to simulate these conditions in a pressure chamber. As a result, pilot trainees were tested under these con-

ditions once, at the beginning of their training. If they got the bends (only mild cases were induced), they were excluded from the training on the grounds that they were more likely to get the bends under battle conditions. This procedure was severely criticized by the statistician Joe Berkson, and he persuaded the Air Force to replicate the test—that is, repeat it several times for each trainee. pl875