## 3 Materials and Methods
### Phase 2: Selecting the Primary Research
Although conference papers may be shorter and often only provide some information in detail compared to journal papers, there is a possibility of also finding quality papers published in conference proceedings. Therefore, at this stage, we decided to also include articles published in conference proceedings. However, before selected papers were finally reviewed for data extraction, they were assessed with the defined quality criteria (see Table 5). We have also followed several criteria (see Table 4) for excluding identified studies from data extraction as follows. With the exclusion criteria E1, the research team decided to restrict the research to the last ten years (2012-2022). The main reason for that decision was to obtain a balanced inclusion of different types of disability. For instance, cognitive accessibility is an issue that only started to appear in research in the last few years. Next, because the same article can be indexed in different databases, and the search in different digital libraries often provides links to the same article, the results of the search were checked for duplicates, which were removed from the final list of selected articles (E2). In this study, we were interested in user-based testing, specifically in computer-based HCI. Therefore, all articles reporting studies of non-computer-related HCI were excluded (E3). The research team also agreed to exclude non-original articles that reported results from existing literature reviews or systematic mapping studies (E4). Finally, to be able to extract all data as specified in Section 3.3, studies for which only abstracts were accessible (E5) were excluded from the final list. In the literature review, we searched for peer-reviewed articles published in journals and proceedings of international conferences. Such publications are expected to have gone through review procedures. However, we still wanted to carry out an additional analysis of the writing quality (Q1) of the articles found. We evaluated the identified articles according to the quality of the writing, checking whether the articles contained well-written essential elements such as an abstract, introduction, materials and methods, discussion, and conclusions from which it is possible to understand the data that interested us in our research effectively. Each article was also assessed based on the quality of the venue (Q2), wherein we checked whether the article was published in a journal with the impact factor as to whether it was in a conference proceeding. Venue quality was mainly based on inclusion in the Journal Citation Reports (for Journals), or the CORE ranking (for conferences). In each article we evaluated, we looked for whether the testing procedures were described and what the quality of the procedure description was. We were interested in whether the description process described different phases such as preparation of tasks, recruitment, execution of the test, etc. (Q3). Since our research aimed to gather barriers and good practices in the inclusion of users with disabilities, the article needed to report the implementation of a study with the inclusion of such users (Q4). We were interested in those studies that, based on practical experience, could provide the challenges in including users with disabilities in the user-based testing and good practices based on practical experience. The process of selecting the relevant literature was carried out in several steps (see Figure 3 and Table 6). In the second step, we limited the set of studies by applying the exclusion criteria E1 to include only studies published in 2012 or later, which resulted in a set of 852 studies. In the next step, removing 34 duplicate entries resulted in 818 articles used for the next step of the selection process. In the fourth step, the exclusion criteria (I1-I4 and E3-E5) were applied to exclude irrelevant studies. Based on titles, reading abstracts, and conclusion, the studies that address user testing of a product or service with people with disabilities were selected.