World of Warcraft, the online role playing game, has introduced an alternative way for youth to entertain themselves and socialize. According to Blizzard, which own World of Warcraft, the number of users that play this game reached 10 million worldwide the last year.

For three years now, when Nick’s friends want to see him, they must drive to his home, because he spends so much time in front of a computer screen playing World of Warcaft. His obsession with the game is such that when he isn’t playing it, he is talking about it. He even shirks his responsibilities to play. Even when he decides to do something else, he looks forward to returning home and logging in again. This behavior has a negative impact on his friendships and social life and it may cost him his studies, which he is ignoring.

“It is the best game ever,” he said. “The fact that it has no end and you have to do something all the time makes it the ideal way of avoiding boredom.”

Dr. Maressa Hecht Orzack, a clinical psychologist at McLean Hospital in Massasuchets, reported that 40 percent of World of Warcraft players are addicted to the game. Orzack said in an interview with the Web site Ars Technical that the number emerged from an online forum.

Orzack, the founder of the Computer Addiction Service, also said that an approach known among psychologists as “variable ratio reinforcement” is used in role playing games. According to this approach, the best way to optimize the desired behavior in the subject is to hand out rewards for correct behavior and then adjust the number of times the subject is required to exhibit that behavior before a reward is handed out. For instance, in  World of Warcraft, the best items in the game are the epic ones distinguished by their purple color. In order to get an epic item as a reward a player needs to kill a monster. But even by killing a monster the player only has a 0.01 percent chance to get that item. So the player might have to kill a lot of monsters to receive one of the epic items.

“These games are very elaborately designed to ease you in gently, entice you, and keep you there,” said Orzack. “And it’s a cycle: people begin to spend too much time playing it and their careers and personal relationships begin to deteriorate.”

Back at his computer screen Nick said: “I play World of Warcraft almost all day because if I stop playing for some days other players will receive better items than me and they will become better. I am not addicted of course, I can stop anytime I want, I just don’t want to now.”

But Nick’s perception that he can quit anytime he wants, and all the other aspects of his new behavior, are listed as psychological symptoms of computer addictive behavior on Orzack’s site, www.computeraddiction.com.