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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


The following sections discuss the design, participants, and task and procedures used in this study.


The experiment was designed as a within-subject test, where dependent variables were the completion time and number of errors, and the independent variable was the type of keypad (conventional vs. randomized). Two separate experiments were conducted based on the length of the PIN to be entered. The first experiment used short (4-digit) PINs, and the second experiment used long (8-digit) PINs.


A total of 50 participants were recruited to participate in the experiment, 25 for each PIN length. The average age of participants was 23.24 years, with a standard deviation of 6.60 years. There were 6 female and 44 male participants, with 39 Caucasians, 10 Hispanics, and 1 Asian.


The randomized keypad and conventional keypad were implemented in software, and appeared on a 19-inch touch screen monitor (Figure 1). The software created a randomly generated PIN on top of the keypad for each trial. When a participant typed the PIN and pushed Enter, the software recorded the completion time and the correctness of the entry. Participants could correct errors with the Clear button until they pressed Enter.

Task and Procedure

Each participant completed a pre-test and post-test questionnaire to collect demographic and subjective data about the user experience with the randomized keypad. Before data collection, each participant entered three PINs to become familiar with the touch screen and keypad. During data collection, each participant completed 20 PIN-entry trials with a conventional keypad followed by 40 PIN-entry trials with a randomized keypad. A PIN for each trial was generated randomly. The randomized keypad was used for 40 iterations to investigate training effects. After the user testing session, each participant completed a post-test questionnaire to collect subjective usability assessment data.

Figure 1

Figure 1. Conventional keypad (left) and randomized keypad on a touch screen

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