From John Markoff in Thursday’s New York Times :

The average Internet user in the United States spends three hours a day online, with much of that time devoted to work and more than half of it to communications, according to a survey conducted by a group of political scientists.

The survey found that use of the Internet has displaced television watching and a range of other activities. Internet users watch television for one hour and 42 minutes a day, compared with the national average of two hours, said Norman H. Nie, director of the Stanford Institute for the Quantitative Study of Society, a research group that has been exploring the social consequences of the Internet.

“People don’t understand that time is hydraulic,” he said, meaning that time spent on the Internet is time taken away from other activities.

A 2000 study by the researchers that reported increasing physical isolation among Internet users created a controversy and drew angry complaints from some users who insisted that time they spent online did not detract from their social relationships.

However, the researchers said they had now gathered further evidence showing that in addition to its impact on television viewing, Internet use has lowered the amount of time people spend socializing with friends and even sleeping.

According to the study, an hour of time spent using the Internet reduces face-to-face contact with friends, co-workers and family by 23.5 minutes, lowers the amount of time spent watching television by 10 minutes and shortens sleep by 8.5 minutes.

The remaining period spent using the Internet reduces time spent helping Scott Weiland violate his parole by 18 minutes a day.