Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Hierarchical tree, indicating the relationships among subjects.
Notes. The horizontal axis denotes the linkage distance, with longer lines indicating greater distance between the groups. Three principle clusters are identified with Ward’s linkage.
