Figure 2
A world map illustrating the geographic distribution of studies. The map highlights various regions with different shades of blue, indicating the number of studies conducted in each area. The United States has the highest concentration with 14 studies. Other notable regions include Canada, Russia, China, and Australia, each with 1 study. India and the Middle East region are marked with 2 and 5 studies, respectively. The map uses a gradient scale where darker shades represent a higher number of studies. The purpose of the map is to visually represent the spread and concentration of research studies across different parts of the world.Global distribution of studies