"Is There a Nexus Between Terrorist Involvement and Mental Health in the Age of the Islamic State? " Combating Terrorism Cent...

"...of 55 attacks in the West where the 76 individuals involved were possibly influenced by the Islamic State, according to media reports, 27.6% had a history of apparent psychological instability, a percentage comparable to that found
..."

https://www.ctc.usma.edu/posts/is-there-a-nexus-between-terrorist-involvement-and-mental-health-in-the-age-of-the-islamic-state