Published in the British Journal of Psychiatry, the study found that Canada had the highest levels of the condition, with Australia, New Zealand, and the US close behind.
The lowest levels were found in places like Nigeria and China.
It is thought that survivors in ‘safe’ affluent societies which are less accustomed to violence on the scale seen in recent terror attacks suffer a profound shock when terrible events occur.
Study co-author Professor Chris Brewin from University College London told the Guardian: “PTSD has often been linked to something that violates your expectations.”
“You thought you were living in a world which is basically safe, people are basically well disposed toward you, and something happens that completely turns those ideas upside down. It is thought that makes it really hard for people to get over these events,” he said.