Pioneering work done by Linda H. Aiken at the University of Pennsylvania in 2002 showed that each extra patient a nurse had above an established nurse-patient ratio made it 7 percent more likely that one of the patients would die. She found that 20,000 people died a year because they were in hospitals with overworked nurses.
Research also shows that when floors are adequately staffed with bedside nurses, the number of patients injured by falls declines. Staff increases lead to decreases in hospital-acquired infections, which kill 100,000 patients every year. (NYT)