# Enhancing E-Learning with Blockchain: Characteristics, Projects, and Emerging Trends
## 3 Methodology
### Data Extraction  
In the 'Identification' phase, the PRISMA approach (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) in Figure 1 was used in our paper selection process. We aimed to gather relevant and reliable research by searching through reputable sources, namely ScienceDirect, Scopus, and Google Scholar. This initial search yielded a total of 710 papers (n = 710). Moving on to the 'Screening' phase, we took steps to eliminate duplicate papers to avoid redundancy and ensure the uniqueness of our review. After removing duplicates, the number of papers decreased to 567 (n = 567). We then applied additional exclusion criteria to further refine our selection. We excluded papers that were not directly related to our specific topic, resulting in the elimination of 291 papers (n = 291). Furthermore, papers that were not written in English were excluded, as well as those published before 2016. Additionally, we excluded editorial articles, opinion pieces, and other non-research articles. This screening process allowed us to focus on papers that were more closely aligned with our research objectives. In the subsequent 'Eligibility' phase, we further refined our paper selection by carefully examining the remaining papers for their relevance to our research question, aims, and objectives. Through this meticulous assessment, we excluded an additional 229 papers (n = 229) that did not meet our criteria. As a result, we arrived at a final count of 47 papers (n = 47) that were directly pertinent to our study. By strictly adhering to the PRISMA approach throughout the review process, including the application of these exclusion criteria in the 'Identification' and 'Screening' phases, we ensured the inclusion of these 47 pertinent papers. This rigorous methodology enhances the reliability and validity of our findings, as it minimizes bias and ensures that the selected papers align with the objectives and scope of our research. The pie graph depicted in Figure 2 represents the distribution of three different databases used in the systematic review. These databases include ScienceDirect, Scopus, and Google Scholar. Each database's contribution is depicted as a percentage of the total. The largest portion of the pie is occupied by Scopus, which accounts for 43.8% of the data used in the system review. This indicates that Scopus played a significant role in providing information and resources for the study. Following closely behind is ScienceDirect, representing 35.5% of the data. ScienceDirect also made a substantial contribution to the system review, though slightly less than Scopus. Lastly, Google Scholar makes up 20.7% of the pie, indicating a relatively smaller but still notable portion. Google Scholar's database  
Figure 1: PRISMA diagram illustrating our literature research methodology. was utilized to a lesser extent compared to the other two, but it still played a meaningful role in the overall study. The graph in Figure 3 shows the contribution of each bibliographic database to the total pool of papers. The number of papers recovered from each database is shown in the blue bar on the left, both in terms of the total number of papers retrieved and as a percentage of those papers. The number of pertinent papers, included and kept, is shown in the orange bar on the right. Again, this number is provided in absolute numbers and as a percentage of all the papers retrieved from that particular database. The pie graph in Figure 4 titled \"Document Types\" illustrates the distribution of document types used in the study. Five distinct classes are represented in the graph, each corresponding to a specific percentage. The largest portion of the pie is occupied by research  
Figure 3: Retrieved and included papers. Figure 2: Document sources. articles, accounting for 41.4% of the total. Review articles make up 13.7% of the document types, while book chapters represent a smaller percentage at 6.8%. Conference papers contribute significantly to the study, comprising 24.4% of the pie.