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.
Network of co‐occurring keywords in the recent LHS literature. Each circle (node) is a keyword, and each line (tie) represents co‐occurrence. Size of node indicate the number of times a keyword was used. Colours represent different clusters of keywords
