According to WISP, the aim was to measure security provider performance across the four domains of internal security: capacity, process, legitimacy and outcomes.
Secondly, to see how these domains relate to each other and finally to track trends in these domains over time, and to inform the work of security providing agencies, researchers, and practitioners in the field of peace and conflict studies, criminology, and police studies.

Check out the list here..USa couldn't find the best 20 :
https://afro9jaland..com.ng/2017/11/20-countries-with-best-police-in-world.html?m=1