## 5 Experiment Results and Discussion
### Experiment Description  
The user testing was conducted with a total of 108 participants, and according to the universal design, the group of participants included people with disabilities and people of different ages. Specifically, 29 people with different disabilities (visual, auditory, physical, cognitive/neurological, specific learning difficulties, multiple disabilities) and 79 people of different ages participated in the user testing. Most of the users with disabilities were recruited in agreement with associations of people with various types of disabilities from Zagreb (Croatia), while to recruit other participants, the study was disseminated among UNIZG FER staff and their contacts. According to research from [74], five participants are sufficient for testing the usability of a solution, as you can find as many usability problems with five users as with many more users, which is not always cost-effective. However, the formula from [74] is valid when it comes to users who use the product in a similar way. When it comes to different groups of users, such as people with different types of disabilities or people with different ages, then it is necessary to test the product with users from each group. Although the user groups are different, there will be some overlap in the findings of errors, so it is recommended that at least three users from each user group be involved if there are three or more user groups [75]. Therefore, in recruiting participants for user testing in this research, care was taken to collect at least the minimum number of participants of people with different types of disabilities and people of different age groups necessary to find relevant usability and/or accessibility problems for each group. The experiment occurred in the spring of 2023 (from April 20 to May 9) in different environments and cities in Croatia, where participants completed the tasks in a real-world setting. The largest proportion of participants tested in the Laboratory for Assistive Technologies and Alternative and Augmentative Communication (ICT-AAC) ([[http://lab.ict-aac.hr/](http://lab.ict-aac.hr/)]([http://lab.ict-aac.hr/](http://lab.ict-aac.hr/)) (accessed on 15 December 2024)) at the University of Zagreb Faculty of Electrical Engineering and Computing (UNIZG FER), while most of the remaining testing locations included the premises of associations for people with different types of disabilities. Two models of Samsung tablet devices (Galaxy Tab S6 Lite, 4/64 GB and Galaxy Tab A8, 3/32 GB) were used for testing the games and filling out the questionnaire. Before participating in the user testing, each participant filled out and signed an informed consent form, which described the scope of the research in which the user testing was conducted, what data was collected, the testing procedure, and how the privacy of each user was ensured. For participants who could not sign the form by themselves, parents or caregivers did that for them. User testing was performed by the main researchers (authors in the paper) with the help of two UNIZG FER students. In the associations with people with disabilities, the participants first listened to a short, 10-min lecture on AR with a demonstration of various applications on tablet devices. The terminology used was adapted so that technological terms are brought closer to people with certain disabilities. The main activities of the user testing included playing the first AR-based serious game (SG1) on a tablet device, then playing the second AR-based serious game (SG2) on a tablet device and filling out the questionnaire created in Microsoft Forms. The total duration of user testing was estimated at 10-15 min per subject, except for testing with participants with certain types of disabilities, which lasted from 20 to 30 min. Additionally, after filling out the questionnaire, a discussion with individual users with disabilities and/or their parents/assistants took place regarding certain accessibility problems and in that case, the entire user testing took longer (up to 45 min).