*3.6. Category Co-occurrence Analysis and a Knowledge Map*

Co-occurrence analysis of subject categories allows us to intuitively understand the main subjects involved in a research field [48]. The classification of the categories in this study comes from the WOS database. In Figure 9, the purple circle on the edge of the node circle indicates that this node has a high intermediate centrality value. In Table 8, we list the top ten subject categories with co-occurrence frequency. Based on Figure 9 and Table 8, the subject categories of global health research are mainly "Public, Environmental and Occupational Health", "General and Internal Medicine", "Health Care Sciences and Services", "Medicine, General and internal" and "Infectious Diseases". It shows that global health research involves multiple disciplines and fields. Based on the analysis of the previous sections, we have drawn a comprehensive knowledge map of global health research, as shown in Figure 10.

**Figure 9.** Knowledge map of co-occurrence categories.



**Figure 10.** A comprehensive knowledge map in the global health research field: 1996–2019.
