The bar chart compares eight types of research methods and their frequency. Report method has the highest count with 8 studies, followed by qualitative with 6, literature review and case study each with 4, and mixed methods and Delphi study each with 3. Quantitative and document analysis have the lowest count with 2 each. The horizontal axis represents frequency, ranging from 0 to 9, and the vertical axis lists the method types. The chart shows that qualitative and report-based approaches are the most frequently used methods in the analysed studies.