# Evaluation of Methodologies and Measures on the Usability of Social Robots: A Systematic Review
## 3 Results
### Evaluation Methods
#### 3.2.2 Evaluation Technique  
We found four types of evaluation techniques from reviewed articles: (1) questionnaires, (2) interview, (3) video analysis, (4) biometrics. Details of techniques were summarized in Table 2.  
Questionnaires. There were 29 studies that used a questionnaire to evaluate HRI. Traditionally it is the most common instrument to evaluate UX so there are various verified questionnaires deployed in industry and academia. When we use a questionnaire to evaluate, it is easy to analyze and show its result in the statistics to others. However, when we want to understand users more behind its answer to a questionnaire, we cannot find any reason from the evaluation. That's why researchers do an interview or conduct any other type of research as a complementary way of a questionnaire.  
In this study, we found many researchers used the questionnaires on users' acceptance of the new product, a social robot which was verified in other previous studies already. They used one specific existing questionnaire or they combine two or more existing questionnaire to meet their research goal. We will introduce some of user acceptance model which is referred to in several studies in the next part of this article.  
Interview. For conducting an interview, an interview can interact with the participant directly or can do telephone interviews. Notably, it is founded that face-to-face interviews were a complementary way of other evaluation techniques and its result was reported as additional opinion with their quantified rating. However, half of the research that conducted an interview targeted subjects who have difficulties to answer to a designed questionnaire--children or cognitively-intact older adult [10; 13; 24]. In this case, an interview can be an alternative to a questionnaire.  
Video analysis. To observe subjects' natural expression and body movement, 10 research analyzed video of the evaluation session recorded by external cameras or the robot. The research used an existing coding scheme to rate each video clip. Multiple researchers analyzed the recorded video and they translate it into quantified data.  
Among 10 studies using a video analysis method, 6 research targeted children or the elderly. There are a number of papers on video analysis to understand various issues related to children or the elderly with dementia [29; 30; 31; 32; 33]. Ref. [20] found that video analysis is an appropriate way to measure users' behavioral and emotional engagement especially people with dementia.  
Biometrics. There were two studies which used biometrics to evaluate social robots [34; 35]. In [34], researchers collected participants' respiration, heart electrical activity, and galvanic skin response (GSR) to verify health benefit from a touch-centered interaction with a social robot. In [35], subjects' heart rate variability (HRV) from electrocardiogram (EKG) and electrodermal responses (EDR) were collected to examine the effect of robotic social therapy on children with autism. Ref. [36] found that the benefit of using biometrics is not only providing an enormous number of usability and UX issues, but also providing validation of issues, and they mentioned the potential of mixed-method approaches.