There are good reasons to be troubled by the violence that spreads throughout the media. Movies, Television and video games are full of gunplay and bloodshed, and one might reasonably ask what’s wrong with a society that presents videos of domestic violence as entertainment. Most researchers agree that the causes of real-world violence are complex. A 1993 study by the U.S. National Academy of Sciences listed “biological, individual, family, peer, school, and community factors” as all playing their parts. Viewing abnormally large amounts of violent television and video games may well contribute to violent behavior in certain individuals. The trouble comes when researchers downplay uncertainties in their studies or overstate the case for causality ( 因果关系 ). Sk eptics were dismayed several years ago when a group of societies including the American Medical Association tried to end the debate by issuing a joint statement: “At this time, well over 1,000 studies... point overwhelmingly to a causal connection between media violence and aggressive behavior in some children.” Freedom-of-speech advocates accused the societies of catering to politicians, and even disputed the number of studies (most were review articles and essays, they said). When Jonathan Freedman, a social psychologist at the University of Toronto, reviewed the literature, he found only 200 or so studies of television-watching and aggression. And when he weeded out “the most doubtful measures of aggression”, only 28% supported a connection. The critical point here is causality. The alarmists say they have proved that violent media cause aggression. But the assumptions behind their observations need to be examined. When labeling games as violent or non-violent, should a hero eating a ghost really be counted as a violent event? And when experimenters record the time it takes game players to read ‘aggressive’ or ‘non-aggressive’ words from a list, can we be sure what they are actually measuring? The intent of the new Harvard Center on Media and Child Health to collect and standardize studies of media violence in order to compare their methodologies, assumptions and conclusions is an important step in the right direction. Another appropriate step would be to tone down the criticism until we know more. Several researchers write, speak and testify quite a lot on the threat posed by violence in the media. That is, of course, their privilege. But when doing so, they often come out with statements that the matter has now been settled, drawing criticism from colleagues. In response, the alarmists accuse critics and news reporters of being deceived by the entertainment industry. Such clashes help neither science nor society.