A Usability Score for Mobile Phone Applications Based on Heuristics

Introduction

Mobile phones are becoming the most popular and widespread personal consumer device (Accenture, 2012). In the last few years, they have rapidly advanced from a simple device to make phone calls to complex multimedia interactive systems (Ji et al., 2006). Such changes in devices have a significant impact on the nature of user interaction. As mobile phones offer new ways of interaction (via gesture, sensors, camera, voice, etc.) their interaction models may differ significantly from traditional ones (Wasserman, 2010). Size and portability requirements of mobile phones present limitations as well as the awkward ways for data input. Especially touch-screen phones pose new challenges through the lack of tactile feedback, key size, etc. (Balagtas-Fernandez et al., 2009). Interface design is further complicated, as mobile phones are used by a wide range of people with different goals anytime in any location (Huang, 2009). This also makes usability an even more important quality attribute of software applications for mobile phones (Treeratanapon, 2012).

Thus, in order to obtain a more complete understanding of users’ needs and to provide better user interaction, it becomes important to measure usability as a part of evaluations and to guide the development of applications. Usability is understood as the extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use (ISO 9241-11). Many techniques are available for measuring usability, including, e.g., the measurement of user satisfaction through post-test questionnaires such as SUS (Brooke, 1996) or SUMI (Kirakowski & Corbertt, 1988). Yet, due to the specific characteristics, there is certainly a great demand in the mobile industry to adopt lightweight evaluation techniques as part of the usability engineering process that can be applied quickly and with minimal effort (Kallio & Kekalainen 2004) as the application development cycle for mobile phones is fairly short (Ji et al., 2006). A popular way to evaluate usability are heuristic evaluations (Nielsen, 1994), a quick, cheap, and easy inspection method for finding usability problems that can be performed without the need to involve real end users or an already working prototype. In heuristic evaluations, a group of usability experts evaluates the compliance of an interface design to a set of usability heuristics in order to identify potential usability problems and to measure usability (Nielsen, 1993).

Usability heuristics used as a basis for such evaluations represent general principles for the design of interfaces such as “visibility of system status” or “user control and freedom” (Preece et al., 2011). They are derived from a mix of theory-based knowledge, experience, and common sense and are used to infer the degree of usability and to identify potential usability problems. These heuristics are broken down into measurable criteria commonly instrumented through questionnaires (also denoted checklists). Such checklists represent measurement instruments with items designed to assess certain aspects of the interface design based on the respective set of heuristics. The results of heuristics evaluations can be used to identify usability problems and to measure usability by expressing how closely the interface design matches the usability heuristics and, thus, inferring its degree of usability on an usability scale (Keevil, 1998).