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Usability Evaluation of Randomized Keypad

Young Sam Ryu, Do Hyong Koh, Brad L. Aday, Xavier A. Gutierrez, and John D. Platt

Journal of Usability Studies, Volume 5, Issue 2, Feb 2010, pp. 65 - 75

Article Contents


Recommendations

According to the pre-test survey, a majority of users had expressed insecurity when they typed PINs in public. This confirms a need for alternative input methods that reduce the feeling of insecurity. Also, a majority of users believed the use of a randomized keypad would improve the perceived security in the pre-test survey. However, according to the post-test survey, only users who performed short (4-digit) PIN tasks maintained this belief. Also, users found the randomized keypad more difficult to use for entering long PINs.

It was obvious that the randomized keypad required additional time to type PINs than the conventional keypad, regardless of the PIN length. However, the randomized keypad caused significantly more errors than the conventional keypad when entering long (8-digit) PINs. Thus, according to the subjective assessment in pre-test and post-test surveys and the objective usability measures, the use of a randomized keypad would be recommended only for short (4 digit) PINs.

Future Research

In this study, the randomized keypad was configured with a fully randomized layout of the ten numeric keys in a standard, square orientation. However, a randomized keypad can be configured in many different ways. For example, in a square keypad orientation, rows can be randomized while columns are fixed. With more creative keypad designs, a circular numeric keypad could be used (i.e., rotary-dial) where the location of the 0 key is randomly selected while the ordering of the keys is not manipulated. Other orientations, such as a strip-shaped keypad or beehive-shaped keypad are feasible because touch-screen devices can produce arbitrary keypad shapes. Thus, the combination of different levels of randomization with novel keypad designs may result in surprising usability when evaluated by other researchers. The tradeoff between the complexity of randomness and the enhancement of perceived security is likely to depend on a combination of factors in keypad design and presentation.

The use of a randomly generated PIN for each trial might have reduced external validity of the study, because most people use familiar PINs that they have already memorized. Thus, the completion time with a conventional keypad and well-known PIN may be much faster than indicated by this study. However, the goals of this test included minimizing the training factor associated with the completion time. Thus, other researchers need to consider whether to use randomly generated PINs or a fixed PIN to evaluate keypads.

Conclusion

In this study, the usability of a randomized numeric keypad was evaluated. Via data collection and statistical techniques, the randomized keypad was compared to the conventional numeric keypad. Completion time and number of errors were used to objectively measure the efficiency and accuracy of each keypad in data-entry tasks of short (4-digit) and long (8-digit) PINs. In addition, subjective measurements including the perceived level of improved security and user satisfaction were assessed. The results indicated that the average completion time with a randomized keypad was longer than that with conventional keypad. This observation was consistent for both short and long PINs. The number of errors with a randomized keypad was significantly higher than with a conventional keypad when using long PINs, while the number of errors with a randomized keypad was not significantly higher than with a conventional keypad when using short PINs. According to the subjective assessment in pre-test and post-test surveys and the objective usability measures, a randomized numeric keypad was more applicable to tasks with short (4-digit) PINs.

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