International Journal of Computer Theory and Engineering, Vol. 5, No. 3, June 2013 500 DOI: 10.7763/IJCTE.2013.V5.737 Abstract—A lot of research has been done on usability evaluation of software systems that results in different usability factors proposed to evaluate the overall usability of a system. Despite the effort, there is no consensus on usability factors and criteria (sub-factors) to determine the appropriateness of these factors with respect to the system and domain under study. This paper attempts to find out which usability factors are more important for haptic systems in particular and for other systems in general. It also attempts to justify the relationship between usability factors and sub-factors for the evaluation of any system. It is found that efficiency, effectiveness, satisfaction, learnability, and safety are the most important factors to be considered for evaluating any haptic system. It also highlights sub-factors that have consistent relationship with these important factors. Furthermore, this work strengthens the available literature related to usability evaluation that mainly focuses on efficiency, effectiveness, satisfaction, and learnability for the evaluation of a system independent of any domain. Index Terms—Usability, factors, haptic systems, criteria, sub-factors. I. INTRODUCTION Usability is not a new concept anymore. Many definitions [1]–[3] are proposed in literature. It is believed [4] that Shackel’s definition “the capability in human functional terms to be used easily and effectively by the specified range of users, given specified training and user support, to fulfill the specified range of tasks, within the specified range of environmental scenarios” [3] is still valid. This definition also provides guidance on usability evaluation of a system i.e. system should support users’ tasks effectively and efficiently with ease of learning. Many other usability models propose different usability factors to assess the overall usability of a system. For example, speed of performance, time to learn, retention over time, rate of errors by users, and subjective satisfactions are proposed by [5] to measure usability. ISO standard 9241:11 [1] highlights efficiency, effectiveness, and satisfaction as major usability factors. Nielsen suggests efficiency, learnability, memorability, safety, and satisfaction as the important factors [6]. We may infer that efficiency, effectiveness, satisfaction, and learnability are considered the most important and common factors as proposed in different models [1], [3], [6]. Manuscript received September 18, 2012; revised December 17, 2012. This work was supported by the graduate assistantship scheme, UTP, Malaysia. Muzafar Khan is with the Department of Computer Science, COMSATS Institute of Information Technology, Islamabad, Pakistan. (e-mail: muzafar_khan@ comsats.edu.pk). Suziah Sulaiman and Abas M. Said are with the Computer and Information Sciences Department, Universiti Teknologi PETRONAS, Tronoh, Malaysia (e-mail: suziah@petronas.com.my, e-mail: abass@petronas.com.my). Muhammad Tahir is with the Faculty of Computing and Information Technology, King Abdulaziz University, Jeddah, Saudi Arabia. (e-mail: mtyousaf@kau.edu.sa). Consolidated usability model proposed by [7] is an attempt to provide comprehensive approach towards usability evaluation. This model highlights 10 usability factors that are efficiency, effectiveness, productivity, satisfaction, learnability, safety, trustfulness, accessibility, universality, and usefulness. To assess these 10 factors, 26 sub-factors are proposed. To measure these major and sub-factors, 127 specific metrics are proposed. Minimal memory load, time behaviour, resource utilization, and operability are few sub-factors associated with efficiency. Layout appropriateness is one of the metrics described in [7]. It is proposed to measure the expected time to complete a task by calculating the frequency of transition and distance between two visual objects. Despite this consolidated model [7], it is still the question of which usability factors are more important or relevant to specific systems or domains. These factors may not necessarily important for all systems. For example, trustfulness is more related to web systems whereas learnability or accessibility can be the most important factor for systems used by people having some disability. Haptic systems are unique in nature as these systems deal with sense of touch i.e. haptic feedback. Haptic feedback is further classified into force and tactile feedback [8]. Sometimes these terms i.e. haptic, force and tactile feedback are used interchangeably. Due to limited work on usability evaluation of haptic systems as discussed in [9], it is worthwhile to find out whether the most common usability factors i.e. efficiency, effectiveness, satisfaction, and learnability are also equally important for haptic systems or any other factors to be considered for these systems. Addition to it, the relationship between major and sub-factors is not justified in [7]. It would be beneficial to explore further this relationship for systems in general that will also help to decide the most appropriate sub-factors for evaluation of haptic systems. This paper attempts to address these issues by conducting interviews with some domain experts (doing research for haptic systems) and a study with a few selected faculty members using card sorting method. The rest of paper is organized as follows: Section 2 provides an insight on the important usability factors for haptic systems on the basis of interviews conducted. Section 3 discusses the relationship between usability factors and sub-factors based on card sorting method. Section 4 provides a discussion on the results obtained and limitations of the study while Section 5 concludes the paper. II. USABILITY FACTORS FOR HAPTIC SYSTEMS As described earlier, we are interested to find out which factors are more important when evaluating the usability of haptic systems. In the following sub-sections, we discuss it in detail. A Study on Usability Factors for Haptic Systems Muzafar Khan, Suziah Sulaiman, Muhammad Tahir, and Abas M. Said