Two recent studies have found that punishment is not the best way to influence behavior.

    One showed that adults are much more cooperative if they work in a system based on rewards. Researchers at Harvard University in the United States and the Stockholm School of Economics in Sweden did the study.

    They had about two hundred college students play a version of the game known as the Prisoner's Dilemma. The game is based on the tension between the interests of an individual and a group. The students played in groups of four. Each player could win points for the group, so they would all gain equally. But each player could also reward or punish each of the other three players. Harvard researcher David Rand says the most successful behavior proved to be cooperation. The groups that rewarded the most earned about twice as much in the game as the groups that rewarded the least. And the more a group punished itself, the lower its earnings. The study appeared last month in the journal Science.

    The other study involved children. It was presented last month in California at a conference on violence and abuse（虐待）. Researchers used intelligence tests given to two groups. More than eight hundred children were aged two to four the first time they were tested. More than seven hundred children were aged five to nine. The two groups were retested four years later, and the study compared the results with the first test. Both groups contained children whose parents used physical punishment and children whose parents did not.

    The study says the IQs of the younger children who were not spanked were five points higher than those who were. In the older group, the difference was almost three points. The more they are spanked, the slower their mental development.