## 3 Results
### Assessment Methods of Usability in the LUse of Rehabilitative Exoskeletons  
We retrieved 15 assessment methods of usability in the use of rehabilitative exoskeletons. Of these, eight deployed quantitative and subjective measurements, four deployed qualitative and subjective measurements, two deployed quantitative and objective types of measurement, and one deployed a mixed type of measurement. These methods are described in detail within the following subsections. Figure 1: Process and results of the search strategy deployed in the current study. 1.1 Quantitative and Subjective Assessment Methods of Usability in the Use of Rehabilitative Exoskeletons  
Quantitative and subjective assessment methods are those providing a measurement in the form of an amount or count and relying on individuals' judgments [23]. _System Usability Scale (SUS)_. Reported by seven of the selected studies [24; 25; 26; 27; 28; 29; 30], this popular and well-accredited instrument was deployed to conduct quick evaluations of usability with users of a broad range of technological devices and interactive systems. It consists of a 10-item unidimensional psychometric questionnaire that is answered on a 5-point Likert-type scale. The SUS is frequently reported by quantitative evidence (e.g., factor analysis) to show good values of validity and reliability indices, such as construct validity and Cronbach's \(\alpha\). On this basis, this method was assigned a score of 13 out of 17 in our critical appraisal checklist. _Ad hoc questionnaires_. Reported by six of the selected studies [30; 31; 32; 33; 34; 35], this type of instrument was most often reported without any evaluation of the dimensionality nor validity nor reliability, as well as with any description of scoring procedures. Therefore, this method was assigned a mean score of 5 out of 17 in our critical appraisal checklist. _Quebec User Evaluation of Satisfaction with assistive Technology 2.0 (QUEST 2.0)_. Reported by five of the selected studies [27; 29; 36; 37; 38], this instrument was deployed to evaluate how users of assistive technologies are satisfied with such devices. It consists of a 12-item bidimensional psychometric questionnaire that is answered on a five-point Likert-type scale. Its dimensions are device (i.e., eight items assessing dimensions/size, weight, adjustments, safety, durability, simplicity of use, comfort, and effectiveness) and service (i.e., four items assessing service delivery, repairs and service of the device, professionalism of the device, and follow-up service), and have been established through statistical techniques such as factor analysis and nomological relatedness. QUEST 2.0 is reported to show good values of validity and reliability indices, such as interclass correlation coefficient (ICC) for the instrument's test-retest and Cronbach's \(\alpha\). On this basis, this method was assigned a score of 11 out of 17 in our critical appraisal checklist. _Visual Analog Scale (VAS)_. Reported by two of the selected studies [33; 35], this instrument was originally developed to evaluate individuals' subjective responses to pain, and can be used to perform usability assessment while using rehabilitative robotic exoskeletons. It consists of one item that is answered on a 10-point Likert-type scale that allows for rating the degree of perceived pain as \"no pain\" (i.e., 0), \"mild\" (i.e., from 1 to 3), \"moderate\" and \"severe\" (i.e., from 4 to 6), \"very severe\" (i.e., from 7 to 9), and \"worst pain possible\" (i.e., 10). The scale is usually graphically complemented by the presence of colored emotion icons, of which the green and smiling ones indicate less pain, whereas the red and suffering ones indicate more pain. Generally, the VAS is reported with no values of psychometric properties. So, this method was assigned a score of 4 out of 17 in our critical appraisal checklist. _AttrakDiff_. Reported by one of the selected studies [28], this instrument was used to assess the perceived qualities of a given interactive system.