Usability is an important quality attribute of a user’s experience when interacting with a system or tool, and it is also an important attribute in helping users to achieve the suggested goals [1
]. With regard to HCI (Human–Computer Interface) and usability, Bevan states in [2
] that standards related to usability can be categorized as being primarily concerned with the use of the product (effectiveness, efficiency, and satisfaction in a specific context of use).
The categorization of Bevan is coherent with the ISO 9241-11 standard [3
], which describes a widely accepted definition of usability. This standard indicates the rules that are needed in terms of ergonomics, hardware, software, and environments in order to obtain good usability for a product or system. Section 8.1 describes the term usability 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”.
1.2. Usability in Virtual Rehabilitation
One of the promising and emerging fields within rehabilitation therapies for different pathologies is virtual rehabilitation (VRh) [6
]. VRh systems are designed to assist clinical specialists and patients in the rehabilitation process [10
]. The use of ground-breaking technologies together with the emergence of entertaining and playful virtual environments (VE) have demonstrated promising results in the rehabilitation process [11
], improving the adherence to treatments [12
]. However, these systems should be tested regarding important aspects such as usability.
Currently, there are different questionnaires that are designed to evaluate usability in general-purpose systems. The best-known usability questionnaire is the system usability scale (SUS) [15
], which measures the feeling of usability of the users when using computer systems. It is composed of 10 questions with a five-point Likert attitude scale (from strongly disagree to strongly agree). This questionnaire has been used in different domains such as: security software [17
], mobile phones [18
], PDA [20
], Social Network sites [21
], wiki sites [23
], serious games [24
], or robotics [25
]. Even though the SUS questionnaire is not specifically designed for VRh systems, it has also been used for rehabilitation purposes due to the lack of questionnaires that focus on VRh systems. Meldrum et al. [26
] tested balance in patients with vestibular and other neurological diseases using VRh and quantified the usability of the Nintendo Wii Fit Plus®
. Duvinage et al. [27
] assessed the usability of a P300 system (using Brain–Computer interfaces) for lower-limb rehabilitation purposes. One considerable advantage of the SUS questionnaire is the reasonable number of questions that are to be answered at the end of the first session. However, the concepts of this questionnaire are too generic (computers, PDAs, Websites, etc.). The main drawback of the SUS questionnaire is that it does not include questions to obtain responses about specific items related to Virtual Rehabilitation.
Another well-known usability questionnaire is VRUSE [28
]. Fitzgerald et al. [29
] assessed the usability of the E-Yoga system using VRUSE, with the goal of improving postural control and biomechanical alignment of the subjects in a rehabilitation process. The VRUSE evaluates a wide range of concepts: functionality, user input, system output (display), user guidance and help, consistency, flexibility, simulation fidelity, error correction/handling and robustness, sense of immersion/presence, and overall system usability. The main drawback of this test is the large number of questions that the patients are required to answer [28
]: the complete questionnaire has 100 questions. This drawback is especially important if the patients involved in a rehabilitation process have neurological and/or cognitive disorders. Other simplified usability questionnaires for VRh with reasonable outcomes are described in [30
], but the drawback of these questionnaires is that the internal consistency has not yet been validated.
Kizony et al. [34
] published the Short Feedback Questionnaire (SFQ), which is a questionnaire that is related to Witmer and Singer’s Presence Questionnaire [35
]. It is composed of eight questions with a five-point Likert attitude scale, and it has been used in virtual reality environments [36
]. The SFQ questionnaire evaluates the user’s sense of presence, perceived difficulty of the task, and any discomfort that users may have felt during the experience. This questionnaire does not focus on VRh systems.
To our knowledge, there are no validated questionnaires for testing usability or satisfaction of virtual rehabilitation systems. A questionnaire for this purpose must have a reasonable number of questions and internal consistency reliability.
Following the definitions of usability in [2
], usability can be divided into three components: efficiency, effectiveness, and satisfaction. Focusing on VRh, efficiency and effectiveness can usually be measured through a clinical trial. With a classical clinical trial, we can compare an experimental group (using a VRh system) with a control group (following a traditional rehabilitation program) by evaluating efficacy and comparing the recovery level of the two groups. With regard to effectiveness, we can measure, for instance, the number of sessions that each group needs to reach a certain level. However, the third component of usability, satisfaction, cannot be evaluated in the same way as efficiency and effectiveness: a reliable and consistent questionnaire (with an adequate number of questions) is necessary to measure the satisfaction of the users.
The aim of the present study is to introduce the USEQ, a user satisfaction questionnaire that is specifically designed to evaluate satisfaction with virtual rehabilitation systems, and to validate their reliability by analyzing their internal consistency.