Living wills are one solution to the anguish of deciding on treatment for a loved one in a coma. The patient’s instructions — theoretically — will be followed by medical staff. But if there is no will, as is normally the case, what would they want? Writing in the Public Library of Science Medicine, David Wendler argues that a computer can outguess relatives.

After reviewing the literature, he found that patients and their relatives only agreed 68% of the time on whether to withdraw or continue treatment. However, when he applied a simple rule and asked unrelated people to make the decision, the rate went up to 78.4%. This rule is that people will accept life-saving interventions if there is at least a 1% chance of recovering their ability of reason, remember and communicate. A computer came up with nearly the same result, 78.5%.

Dr Wendler now wants to refine his computer’s criteria to take into account sex, age, educational level, religion and so on. It might be able to predict a patient’s wishes with an accuracy of 90%. This might relieve the pressure on relatives who have to make the difficult decision to pull the plug on a life support machine. It might also make it easier on doctors and bioethicists if they can leave life-and-death decisions to a computer.