Want to know what will make you happy? Then ask a total stranger -- or so says a new study from Harvard University, which shows that another person's experience is often more informative than your own best guess.

The study, which appears in the current issue of Science, was led by Daniel Gilbert, professor of psychology at Harvard and author of the 2007 bestseller "Stumbling on Happiness," along with Matthew Killingsworth and Rebecca Eyre, also of Harvard, and Timothy Wilson of the University of Virginia.

"If you want to know how much you will enjoy an experience, you are better off knowing how much someone else enjoyed it than knowing anything about the experience itself," says Gilbert. "Rather than closing our eyes and imagining the future, we should examine the experience of those who have been there."

Previous research in psychology, neuroscience, and behavioral economics has shown that people have difficulty predicting what they will like and how much they will like it, which leads them to make a wide variety of poor decisions. Interventions aimed at improving the accuracy with which people imagine future events have been generally unsuccessful.

So rather than trying to improve human imagination, Gilbert and his colleagues sought to eliminate it from the equation by asking people to predict how much they would enjoy a future event about which they knew absolutely nothing -- except how much a total stranger had enjoyed it. Amazingly enough, those people made extremely accurate predictions.

In one experiment, women predicted how much they would enjoy a "speed date" with a man. Some women read the man's personal profile and saw his photograph, and other women learned nothing whatsoever about the man, but did learn how much another woman (whom they had never met) had enjoyed dating him. Women who learned about a previous woman's experience did a much better job of predicting their own enjoyment of the speed date than did woman who studied the man's profile and photograph.

Interestingly, both groups of women mistakenly expected the profile and photo to lead to greater accuracy, and after the experiment was over both groups said they would strongly prefer to have the profile and photograph of their next date.

In the second experiment, two groups of participants were asked to predict how they would feel if they received negative personality feedback from a peer. Some participants were shown a complete written copy of the feedback. Other were shown nothing, and learned only how a total stranger had felt upon receiving the feedback. The latter group more accurately predicted their own reactions to the negative feedback. Once again, participants mistakenly guessed that a written copy of the feedback would be more informative than knowledge of a total stranger's experience.

"People do not realize what a powerful source of information another person's experience can be," says Gilbert, "because they mistakenly believe that everyone is remarkably different from everyone else. But the fact is that an alien who knew all the likes and dislikes of a single human being would know a great deal about the species. People believe that the best way to predict how happy they will be in the future is to know what their future holds, but what they should really want to know is how happy those who've been to the future actually turned out to be."

Gilbert's research was funded by the National Science Foundation.