Users of Apple's iPhone are experiencing higher text entry error rates than owners of traditional hard-key Qwerty handsets, a usability expert claimed today.

Chicago-based consultancy User Centric compared the texting experiences of iPhone owners and non-owners across devices.

The results suggest that the iPhone's touch keyboard is "overly sensitive" despite the iPhone's overall high usability.

User Centric collected data from 60 participants who entered specific text messages and completed mobile device tasks.

The experiment involved 20 iPhone users who had owned the handsets for at least a month, 20 hard-key Qwerty phone owners and 20 numeric phone owners (multi-tap texters) entering six fixed-length text messages.

Non-iPhone owners also entered six messages on a test iPhone and a phone of another type.

The iPhone owners entered text as rapidly as Qwerty owners on their own phones, but made "significantly more" errors on their own phone (5.6 errors per message) than Qwerty owners (2.1 errors per message) and numeric phone owners (2.4 errors per message) on their own phones.

Comparing texting performance between iPhone owners and novices (non-owners) on the iPhone found no significant difference in error rates.

"While the iPhone's corrective text feature helps, this data suggests that iPhone users who have owned the device for a month still make about the same number of errors as the day they got it," said Gavin Lew, managing director at User Centric.

The consultancy also compared users' performance on unfamiliar phones. Numeric phone owners performed faster text entry on a hard-key Qwerty phone than on the iPhone, and made significantly fewer errors on the hard-key Qwerty devices.

"The iPhone is a great switch from a numeric phone. But if you are switching from a hard-key Qwerty phone, try the iPhone in the store first," said Lew.