Evaluation of Pointing Efficiency on Small Screen Touch User Interfaces

Researchers have been investigating screen designs for small screen touch user interfaces (UIs), but further research is still required for smaller-screen devices including current smart phones. This paper reports on our evaluation of pointing efficiency on devices with touch-by-stylus small screen UIs. User performances were measured by experiments with three devices: a mobile phone, a PDA and a tablet PC. The size of pointing targets was designed so that the target index of difficulty (ID) by Fitts' law ranged in a consistent interval among the three devices. Users' pointing speed and accuracy were compared in terms of throughput and error rate respectively. It is found that the throughput and the error rate for the mobile phone were significantly smaller than those for the PDA and the tablet PC. It is also found that the error rate was not significantly larger in the case where users performed tasks with the mobile phone held by their hands than in the case where they did with the mobile phone put on desktop, although it was in the case of the PDA.