Internet use appears to cause a decline in psychological well-being, according to research at Carnegie Mellon University.

Even people who spent just a few hours a week on the Internet experienced more depression and loneliness than those who logged on less frequently, the two-year study showed. And it wasn't that people who were already feeling bad spent more time on the Internet, but that using the Net actually appeared to cause the bad feelings.

Researchers are puzzling over the results, which were completely contrary to their expectations. They expected that the Net would prove socially healthier than television, since the Net allows users to choose their information and to communicate with others.

The fact that Internet use reduces time available for family and friends may account for the drop in well-being, researchers hypothesized. Faceless, bodiless "virtual" communication may be less psychologically satisfying than actual conversation, and the relationships formed through it may be shallower.

Another possibility is that exposure to the wider world via the Net makes users less satisfied with their lives.

"But it's important to remember this is not about the technology; it's about how it is used," says psychologist Christine Riley of Intel, one of the study's sponsors. "It really points to the need for considering social factors in terms of how you design applications and services for technology."