Hardly surprisingly the attacks of September 11, 2001 had a huge psychological impact on those who were caught up in them but most studies so far have focused on the prevalence of post-traumatic stress disorder (PTSD) and depression rather than other types of mental-health problem. Researchers from the University of Manitoba in Canada used data from the National Epidemiologic Survey on Alcohol and Related Conditions involving 34,683 people. The participants in the study were asked about their mental health and classified into four groups: no experience of 9/11; indirectly experienced 9/11 (i.e. watched it happen on television); close friend of family member injured or died in 9/11 and directly experienced and/or injured in 9/11. The study found that the more people had been exposed to 9/11 the more likely they were to develop mental-health problems including anxiety as well as PTSD and depression. People who had directly experienced 9/11 had six times the risk of developing PTSD, two-and-a-half times the risk of having an anxiety disorder and nearly double the risk of having any mental-health problem.
Christine A. Henriksen, James M. Bolton and Jitender Sareen - The psychological impact of terrorist attacks: examining a dose-response relationship between exposure to 9/11 and axis I mental disorders Depression and Anxiety 27: 993-1000 (2010)