But critics say that a software tool simply could not possibly capture all of the factors and subtleties that go into such decisions. What is more, they say, such a system would also face political obstacles. To wit: the controversy sparked over the 2005 case of Terri Schiavo, 41, whose parents sued to stop Schiavo's husband from removing the life support of his wife, deemed by the Florida court to be in a persistent vegetative state. [See note below.] The Supreme Court ultimately ruled in the husband's favor, but only after the state's governor and Congress tried to block the move.

"After the Schiavo case [many surrogate decision makers] started declining death, for religious and philosophical reasons," says William Smucker, associate director, family medicine center, at Summa Health System in Akron, Ohio. "People's minds change" because of political and other pressures, he notes, wondering if a database could continually change to reflect such potentially decision-altering issues.

There's also the matter of computers trumping family. "There's the question of what Schiavo would have wanted if her husband weren?t around to make a decision," says Steven Miles, professor of medicine and bioethics at the University of Minnesota. "I can't imagine anyone running 'HAL 9000' against her parents."

But Wendler holds that rather than serve as a substitute, a computer might provide a guide for the human surrogate decision makers.

"This treatment indicator is a good starting point for discussion with families," Dr. Smucker says. "Most are making this decision for the first time, and often they have no idea what to do. This gives some normal parameters, and I can say, 'Well, most people in this situation chose treatment X.' That may give them some reassurance."

[Editor's note: A previous version of this story incorrectly stated that Terri Schiavo was brain-dead. Judge George Greer held that Terri Schiavo was in a persistent vegetative state. Schiavo's parents disagreed with his ruling.]