## 3 Results
### Assessment Methods of Usability in the LUse of Rehabilitative Exoskeletons
It consists of a 28-item three-dimensional psychometric questionnaire that is answered on a 7-point Likert-type scale. Its dimensions are pragmatic quality, hedonic quality, and attractiveness. Whereas AttrakDiff is reported to show good values of Cronbach's \(\alpha\) as an indicator of reliability, it lacks evidence of validity. On this basis, this method was assigned a score of 10 out of 17 in our critical appraisal checklist. _Self-Assessment Manikin (SAM)_. Reported by one of the selected studies [38], this instrument was deployed to assess the individuals' emotional response to a stimulus, such as using an upper-limb robotic exoskeleton for motor rehabilitation purposes. It consists of three graphical items allowing users to rate pleasure (i.e., from \"happy\" to \"unhappy\"), arousal (i.e., from \"excited\" to \"calm\"), and dominance (i.e., from \"controlled\" to \"in control\") on a nine-point scale. Whereas SAM is reported to show good content validity and acceptable respondent burden, it lacks evidence of reliability, and descriptions of scoring procedures are not provided. Thus, this method was assigned a score of 11 out of 17 in our critical appraisal checklist. _Heuristic evaluation._ Reported by one of the selected studies [31], this instrument was deployed with a hand robotic exoskeleton for rehabilitation. It consists of a set of up to 29 open-ended questions that are answered by SMEs. While providing a clear definition of its target population, the instrument lacks evidence of both validity and reliability. Therefore, this method was assigned a score of 2 out of 17 in our critical appraisal checklist. _Perceived Rate of Exertion (PRE)._ Reported by one of the selected studies [35], this instrument was deployed to perform assessments of individuals' physical effort, such as in the case of using a wearable robotic exoskeleton for motor rehabilitation of the upper limbs. It consists of one item used to rate the perceived physical effort on a 10-point Likert-type scale, where one corresponds to \"very light activity\", two and three correspond to \"light activity\", four to six correspond to \"moderate activity\", seven and eight correspond to \"vigorous activity\", nine corresponds to \"very hard activity\", and ten corresponds to \"max effort activity\". While PRE is reported to show a very good reliability, it lacks evidence of content and construct validity, as well as a clear definition of its underlying conceptual model and a description of the scoring procedures. On this basis, this method was assigned a score of 7 out of 17 in our critical appraisal checklist. 1.2 Qualitative and Subjective Assessment Methods of Usability in the Use of Rehabilitative Exoskeletons  
Qualitative and subjective assessment methods are those used to collect data in the form of words, sentences, or descriptions of a phenomenon, and relying on individuals' judgments [23]. _Observation._ Reported by two of the selected studies [39; 40], unstructured observations were conducted to assess the usability of two different rehabilitative exoskeletons. The articles examined included a description of both the target population and the scoring procedure. In addition, SMEs were involved in the design of observations. However, no evidence for validity nor reliability was reported. On this basis, this method was assigned a score of 3 out of 17 in our critical appraisal checklist. _Focus group._ Reported by one of the selected studies [41], this method was deployed to detect potential usability issues in a lower-limb rehabilitative exoskeleton. No evidence for construct validity nor reliability was reported. However, a semi-structured facilitator guide was used to standardize the facilitator's conduct across the focus groups. On this basis, this method was assigned a score of 5 out of 17 in our critical appraisal checklist. _Semi-Structured interview._ Reported by one of the selected studies [42], this method was deployed to assess the usability of a lower-limb rehabilitative exoskeleton.