Usability risk level evaluation for physical user interface of mobile phone

The mobile phone has become an indispensable device in everyday life. However, many usability problems were generated by the multi-functionality of mobile phones. There was an important increase on the user interface (UI) design and usability. With the introduction of a variety of forms and keypads in mobile phones, the user's need of controllability, grip-stability, and usability were raised in the UI aspect. Therefore, in this study, we investigated the physical user interface (PUI) elements of mobile phones, and defined the degree of usability risk such as key level value, function level value, and grip level value. Also, this study proposed an evaluation framework to quantitatively measure the usability risk in the mobile phone PUI elements. For this, the mobile phone PUI elements were analyzed and classified by key type, function, and form-factor. Hence, in the case study was investigated and evaluated 133 mobile phones in the market by the proposed framework. As a result, the proposed evaluation framework enabled the measurement of the mobile phone usability risk level in the early stages of the concept design. This made possible the prediction of design problems related with the mobile phone PUI.