# An Agile Approach to Improve the Usability of a Physical Telechabilitation Platform
## 4 Results and Discussion
### Fourth Iteration  
The fourth iteration began in August 2018. In this iteration, 17 mock-ups were re-designed taking into account the feedback from the previous iteration. The same usability evaluation methods and instruments as the previous iteration were used. Six experts and 12 participants (five female and seven male) were invited for the fourth iteration. In the heuristic evaluation, the experts reported a total of 364 heuristic violations in the mock-ups. However, the questionnaire interface had only three usability problems of minor severity. This value had been decreasing in severity throughout the whole evaluation process. Figure 10 shows the frequency of heuristic violations per interface. The results show an increase in the number of usability problems. The increase is due to a greater number of interfaces evaluated and a greater number of experts who participated in the evaluation. The advantage of having greater criteria diversity was that it detected a greater number of usability problems. The disadvantage was the risk of it becoming an infinite cycle of refinements. The Control Request Form proposed in a previous study [27] was used to avoid this risk. The Control Request Form allows one to keep a record of the changes performed in each iteration. The document prevented the recommendations of each new group of experts becoming repetitive and contradictory. Experts placed more significant importance on interfaces UI-9, UI-10, UI-11, UI-12, and UI-13. These interfaces are more related to the objectives of the project. Figure 9: Workload of the six dimensions of NASA-TLX. Table 6 shows the comparative results for iterations three and four regarding heuristics violations according to the severity scale described in Table 3. In the third iteration, the experts reported 38 minor usability problems (41.30%), 23 major usability problems (25.00%), and four usability catastrophes (4.35%) in the 14 mock-up interfaces. The experts reported that the three interfaces with major quantity heuristic violations were: UI-1 (11), UI-2 (9), and UI-4 (8). In the fourth iteration, the experts reported 141 minor usability problems (38.74%), 10 major usability problems (2.75%), and zero usability catastrophes in the 17 mock-up interfaces. The experts reported that the three interfaces with the largest number of heuristic violations were UI-11 (37), UI-7 (32), and UI-6 (31). In the fourth iteration, the NASA-TLX test was also executed. Table 7 shows the comparative results of iterations three and four for the user workload when performing the task T2 \"Perform an active exercise\" using the interface UI12 \"Acute Rehabilitation: Active Exercise (3/3)\". Figure 11 shows some details of the distribution of the global workload through the six dimensions of NASA-TLX. The most significant workload is located in the Performance dimension of the three tasks defined for the experiment. Task T1 had the highest workload through the six dimensions. Since the Performance dimension measures the degree of user dissatisfaction with their level of performance when completing a task, the authors deduce that this result is attributable to the inexperience of users \begin{table}
\begin{tabular}{c c c} \hline \hline
**Severity Rate** & **Third Iteration** & **Fourth Iteration** \\ \hline Catastrophe usability problem & 4 (4.35\%) & 0 (0\%) \\ Major usability problem & 23 (25.00\%) & 10 (2.75\%) \\ Minor usability problem & 38 (41.30\%) & 141 (38.74\%) \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Heuristic violations ordered by severity: third and fourth iteration. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Task** & **Interface** & **Third Iteration** & **Fourth Iteration** \\ \hline T2 & UI12 & 30.67 & 28.67 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Global workload for task T2: third and fourth iteration. Figure 10: Frequency of heuristic violations per interface (UI-1 to UI-17): fourth iteration. with telerehabilitation systems and rehabilitation processes.