# Site Clustering Indices

In the spatial analysis of clinical trial infrastructure, does the clustering of research sites indicate structural concentration in African compared to European research networks? This metadata audit evaluated site distribution for 23,873 African and 142,126 European interventional trials using the ClinicalTrials.gov API v2 location module through March 2026. Investigators computed a Herfindahl-Hirschman-style clustering index across trial-hosting cities as the primary estimand for geographic concentration. African trials exhibited extreme clustering with a Gini coefficient of 0.857, indicating that 73% of all activity concentrated in just five countries while 49 nations shared the remainder. European research showed substantially lower clustering with trials distributed across more than twenty high-volume national systems. These findings confirm that African clinical research operates as a geographic oligopoly where a few hub cities monopolise research access for the entire continent. Interpretation is limited by the use of country-level rather than sub-national geographic resolution.

## References

1. Siegfried N, et al. "Where does all the money go? An analysis of the global funding for clinical trials." Cochrane Database Syst Rev. 2022.
2. Ndounga Diakou LA, et al. "Mapping of clinical trials in sub-Saharan Africa." Trials. 2022;23:490.

## Note Block

- Type: research
- App: https://mahmood726-cyber.github.io/africa-e156-students/geographic-equity/dashboards/angle-12_site-clustering-indices.html
- Code: https://github.com/mahmood726-cyber/africa-e156-students/blob/master/geographic-equity/code/angle-12-site-clustering-indices.py
- Data: ClinicalTrials.gov API v2
- Date: 2026-04-05