Teens take more risks than adults because they weigh risk versus reward differently, says Laurence Steinberg, a developmental psychologist at Temple. To analyze teen risk-taking, Steinberg used a video game which rewards players for taking a certain amount of risk but punishes them for taking too much. When teens drive the course alone, they take risks at about the same rates that adults do. But teens take twice as many risks when friends are watching. "They didn't take more chances because they suddenly downgraded the risk," says Steinberg. "They did so because they gave more weight to the payoff."