# Evaluation of Methodologies and Measures on the Usability of Social Robots: A Systematic Review
## 3 Results
### Evaluation Dimensions
#### 3.3.4 Categorization of Social Robot's Evaluation Measures  
Since the objective of this article was to establish evaluation dimensions for HRI research, we reviewed 167 measures from 36 articles and classified them into four main dimensions: (1) ease of use, (2) usefulness, (3) trust, and (4) emotional attractiveness. When we evaluate a social robot in the utilitarian aspect, ease of use and usefulness will be considered as important dimensions. However, when we want to evaluate a social robot in terms of hedonic aspect, emotional attractiveness is more important than ease of use or its usefulness. Finally, there is a unique dimension, trust. It is traditionally used to evaluate a media which contain and deliver contents to others and nowadays, a social robot could be one of the media that can deliver contents to users. So we found out that trust is a meaningful dimension in evaluating a social robot which needed to build a relationship with users. Those three dimensions build user's attitude toward a robot, and each of the dimensions will meet a specific goal of evaluation (Figure 2). Uilitarian Aspect. There are two sub-dimensions on assessment measures in utilitarian aspect: ease of use, usefulness. Ease of use, as mentioned previous part, ease of use can be defined as \"the degree to which a person believes that using a particular system would be free of effort.\" [39]. Ease of use was addressed in TAM, UTAUT and Almere model. Additionally, there were numerous research to define and evaluate ease of use in UX studies. Ease of use is regarded as an important dimension in HRI aspect. When people are first exposed to a brand-new technology or product, a degree of ease of use can act as an entry barrier. People do not use a product or technology just because it is easy to use, however they will not use it consistently when they find it isn't easy to use. This element is a minimum requirement to use, and it can be a must-be quality in KANO model. From previous UX research, they divided the task into sub-process (e.g., command, procedure, feedback and recovery) and evaluate ease of use in each process. However, a task is ambiguous when people interact with a social robot. Therefore, there are not specific constituents of ease of use in HRI studies. All of the measures of ease of use that founded from studies we reviewed are categorized in Table 4.  
The second factor is usefulness. In TAM [39], perceived usefulness was defined as \"the degree to which a person believes that using a particular system would enhance his or her job performance\". Usefulness was traditionally a main dimension of attitude toward technology with ease of use. After defined in TAM, it is referred to Almere recently. It was a significant determinant to evaluate the functional acceptance of a utilitarian system. Social robot is a hedonic system but also a utilitarian system partly. As in the case of ease of use, a social robot should provide at least minimum acceptable usefulness to overcome a barrier of entry to the market and users. To evaluate usefulness, there are two sub-categories: (1) capability of a social robot, (2) satisfaction from a social robot's advice. However, it is difficult to categorize measures into two sub-categories based on its definition of words. In this study, we consolidate all measures of usefulness in Table 5 regardless of two sub-categories. Figure 2: Dimensions of attitude toward a robot. Hedonic Aspect. There are three sub-dimensions on assessment measures in hedonic aspect. Overall emotional attractiveness is a main component to measure a social robot in hedonic aspect and appearance of the robot, personality of a robot, perceived emotional value of a robot are sub-dimension of emotional attractiveness. In this study, we propose the term \"emotional attractiveness\" as an umbrella term to signify perceived enjoyment and users' feeling. Perceived enjoyment is referred to revised TAM [41] and it is defined as a hedonic motivation in UTAUT and Almere [46; 47].