Punishment or Reward: Which Works Better on Behavior?

It seems like 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 game known as the Prisoner's Dilemma.
They are divided into groups of four. Each members can reward or punish each of the other three players.
The result was that the group that rewarded the most gained 2 times more than the groups that rewarded the least. Also, the group with the most punishment had 25 percent less points than the group with the least punishment.
I think the study made us clear that Rewarding works better than to punish.
Although there are some people who work hard as they punished, people in general feel better and try to do their best if they can get the reward.