## 4 Case Study

Table 5: _Cont._Phase 4: Explore the serious games; the expert explores each serious game with the instructions defined in phase 3. The tasks that the user had to perform were: (1) interact with the first interface of the serious game; (2) review the functionality of each round; (3) identify whether the games have a screen magnifier; (4) review whether the games have the option to adjust the game parameters; (5) determine whether the game has the opportunity to help the user; (6) identify whether the user can read each message of the serious game; (7) review whether the images have adequate clarity and are apparent to the user; and (8) check whether the serious game has the option to change the language. At this stage, the evaluators navigate all the serious game features to detect potential accessibility barriers. Finally, in this phase, the evaluators review the behaviors agreeing to the device used, the browser, and the structure applied. Phase 5: List the barriers; we selected 28 barriers based on WCAG 2.1 for low vision users to apply this BW-based heuristic method. Table 6 contains the guideline identifier, the barrier, the WCAG 2.1 principle, the success criteria, and the level of accessibility. Phase 6: Evaluate with the heuristic method, the evaluators carried out the following process: (1) run the serious game; (2) carefully examine whether each barrier meets the parameters of effectiveness, productivity, security, and satisfaction; we applied Table 1. (3) Find the impact related to the parameters defined in Table 1; (4) record the persistence of each barrier according to the parameters defined in Table 2; (5) apply the persistence scale defined in Table 2; (6) finally, apply the severity scale according to the impact and resulting persistence defined in Table 3.  
To analyze the severity of a barrier, we need two parameters: (1) the impact of the barrier as a result of the effectiveness, productivity, security, and satisfaction of the user performing an activity; (2) the value of persistence, denoted by the number of times the barrier is repeated, is essential when evaluating a serious game. For example, when checking the barrier \"Accessible keyboard\" in the game SG01 \"Acid-base solutions\", we apply the following process: First, for the efficiency parameters, we register the value zero (0), in productivity the value of one (1), in satisfaction zero (0) and security the value of one (1). Second, we analyze whether the barrier affects productivity, satisfaction, effectiveness, or safety. In that case, the impact was minimal; when analyzing these parameters, the impact's value is two (2). Thirdly, we evaluate the number of times the barrier corresponding to the persistence parameter presented by the barrier \"Accessible keyboard\" is presented. Fourth, we apply the persistence scale defined in Table 2. Fifth, we determine the severity defined in Table 3 for impact and persistence; for the barrier \"Accessible keyboard\" we have in the impact the value of two (2) and for the persistence the value of two (2), therefore the severity for the barrier \"Accessible keyboard\" is significant. Phase 7: Record the data; the data from each serious game evaluated was documented in a spreadsheet. Table 7 is an example since it collects the data of only one set; it contains the identifier assigned to the pattern, the barrier, the effectiveness, the productivity, the satisfaction, the safety, the impact, the range of persistence, the total persistence, the result of persistence and the severity of the serious set with the code SG01 that corresponds to \"acid-based solutions\" of the PhET project of the University of Colorado. For the G01 \"Accessible keyboard\" barrier, we applied Table 1 and obtained the following results: in effectiveness we recorded zero (0), in productivity one (1), in satisfaction zero (0), and in safety one (1).