People love iPod because it can fit their mood like a glove, a top academic has discovered.

Sussex University professor Dr Michael Bull is the world's leading authority on personal-stereo useage, and has conducted extensive interviews with iPod users.

He told the Economist: "The iPod grants users far more control over how and where they listen to their music. If none of the music they are carrying with them fits their mood, people prefer not to listen to music at all.

"The large capacity of a hard-disk-based player does away with this problem. The right music can always be summoned up depending on your mood, the time of day, and your activity."

He adds that the iPod allows its users to "escape into their own little private bubbles", adding: "When standing in line at the airport, or waiting for a late train, iPod users feel that not everything, at least, is out of their control."

Bull goes on to explain why iPods do not make their users anti-social. "It makes music consumption, a traditionally social activity, even more so. You can use your iPod as a jukebox at home, and the ability to carry your music collection with you means you can always play new tracks to your friends. Many iPod users compile special selections of tunes, or playlists, for family listening while in the car. Family members negotiate the contents of the playlist, so that Disney tunes end up juxtaposed with jazz and Justin Timberlake."

Video phone
Bull thinks the call for Apple to add phone or video functionality to the iPod is mistaken: "iPod users are far more selective about answering their mobile phones. That suggests that adding phone functionality to the iPod would be a bad idea, since it would facilitate intrusion.

"And people don't watch movies while walking the dog, make playlists of their favourite movie scenes, or clamour to buy individual scenes online. Portable video-players, which are already starting to become available, undoubtedly have their uses, such as providing entertainment during long journeys. But they seem unlikely to be the kind of industry-changing products that the iPod and its imitators have unexpectedly proven to be."