People spend nearly half of their waking hours not thinking about what they are actually doing, according to a US study conducted via the iPhone.

More than 2,200 volunteers downloaded an app which then surveyed them about their thoughts and mood at random times of day and night.

The study from Harvard University suggested minds wander, even from demanding tasks, at least 30% of the time and has found a direct link between being unhappy, and having an overall lack of focus on what you are doing during the day.

The iPhone was a novel research tool for researchers at Harvard University. Participants agreed to be contacted, at which point they selected what they were doing from a menu, whether they were actually thinking about it, and how happy or sad they felt.

While their study sample was composed entirely of people who owned the device, and were prepared to download and be disturbed by an app of this kind, the researchers said it provides an insight into how our minds can wander during the day.

After gathering 250,000 survey results, the Harvard team concluded that this group of people spent 46.9% of their time awake with their minds wandering.

Dr Matthew Killingsworth, one of the researchers, said: "Mind-wandering appears ubiquitous across all activities. "This study shows that our mental lives are pervaded, to a remarkable degree, by the non-present."