## 4 Evaluation and Results  
A quantitative user evaluation of the adaptation of the HybridPLAY system for the elderly was carried out during the month of June 2018. A total of 8 seniors tested the system, who were recruited by verbal communication through the neighborhood of the El Pilar area in Valencia (Spain). Each person played each of the proposed mini-game twice; for the purpose of this experiment, we established that the mini-games were completed when the user collected five squares. Before that, we explained them the dynamics of the mini-games and showed them how to interact with the platform, highlighting the relevance of the verbal communication to succeed fulfilling the given objectives (collecting squares). We provided them with the sensor and with the mobile phone (a Motorola G4 plus), which included the mini-games. We also explained how to clamp the sensor, but users decided where to place it, and in which order they wanted to test the different OFEs. After testing the system, they filled out a pair of questionnaires that were related to the usability of the system and to the individual's satisfaction with the proposed activity. The System Usability Scale (SUS) [27] was chosen to measure usability, whereas a customized satisfaction questionnaire was used to assess several aspects of how users perceived the system, including how HybridPLAY could affect their desire to take exercise. The complete session took about 2 h.  
The participants were senior adults (+50 years old). In Table 1, the socio-demographic data of the participants is provided, showing their mean age, standard deviation (s.d.) and minimum and maximum age. Other parameters shown are gender, how often they use video games and how often they use the park elements, where the range 0-4 for the frequency (f.) means--0: never or almost never; 4: every day. As can be seen, most participants were not regular users neither of video games nor of park elements, although a small percentage of users reported some previous regular experience with OFE. The results of the SUS questionnaire are listed in Table 2. In questions 1 to 10 the range 0-4 means--0: strongly disagree, 4: strongly agree. The values of the SUS score, which are calculated according to [27], however, range from 0 to 100, with 100 being the best possible result. In this case, the score reaches 69.38 points, meaning that the system is above average and is perceived as usable and acceptable. This result can be compared to the group of children and younger adults that previously tested the system and that was presented in Reference [9], where a very similar experiment was carried out for that group, also fulfilling a SUS and a satisfaction questionnaire. In that case, the obtained SUS scores were of 84.92 points for adults and 91.23 points for children. In any case, the results of the current study show that HybridPLAY could be successfully adapted for senior adults, taking into account the fact that a minimum score of 68 would be deemed acceptable for a tool [28; 29]. Nevertheless, it becomes evident that the scores provided by the SUS test reveal that significant further efforts need to be applied in order to fully engage senior people, who are more reluctant to adapt to this technology. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline _Age_ & **Mean** & **s.d.** & **Min** & **Max** & & \\  & 68.37 & 10.82 & 51 & 79 & & \\ \hline \multirow{2}{*}{_Gender (\%)_} & **male** & **female** & & & & \\  & 50.00 & 50.00 & & & & \\ \hline \multirow{2}{*}{_Video game frequency (\%) and mean 0–4 value_} & **f. 0** & **f. 1** & **f. 2** & **f. 3** & **f. 4** & **mean** \\  & 75.00 & 0.00 & 12.50 & 12.50 & 0.00 & 0.625 \\ \hline \multirow{2}{*}{_Using OFE frequency (\%) and mean 0–4 value_} & **f. 0** & **f. 1** & **f. 2** & **f. 3** & **f. 4** & **mean** \\  & 50.00 & 25.00 & 12.50 & 0.00 & 12.50 & 1.414 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Socio-demographic data of the participants.