Using an iPhone application called Track Your Happiness, Harvard psychologists found in a recent study that daydreaming is associated with lower levels of happiness.

The study, published in the most recent issue of Science magazine, periodically polled more than 2000 adults who reported what they were doing, whether their minds were wandering, and how happy they were on a scale of 1 to 100.

The study found at any given time, almost half of the test subjects were thinking about something other than the situation at hand. In any given situation, subjects were likely to be “mind-wandering” at least 30 percent of the time, except during sex, during which their minds wandered only 10 percent of the time.

The paper was co-authored by Harvard doctoral student Matthew A. Killingsworth and Psychology Professor Daniel T. Gilbert, who doubted whether the unique evolutionary trait of “mind wandering” in humans has any significant emotional advantage.

“Even during unpleasant activities, when it would seem beneficial to be day-dreaming, we found that mind-wandering doesn’t lead to higher happiness,” Killingsworth said, pointing to commuting as an example.

The psychologists performed a time-lag test to assess whether it was unhappiness that prompted people to daydream, or vice versa.

The results showed subjects who were mind-wandering were more likely to be unhappy 15 minutes later. In contrast, subjects who were unhappy were no more likely to be mind-wandering after the same 15 minutes.

Perhaps most surprising of all, the content of one’s daydream seems to have little effect on level of happiness. Those whose thoughts wandered to more pleasant topics had only slightly higher happiness levels than those wandering to unpleasant or neutral topics, but they still had lower happiness levels than those focused on the present.

“The ability to think about what is not happening is a cognitive achievement that comes at an emotional cost,” the authors concluded in their paper.