Published March 23, 2026

A new University of Iowa study found that mental illness is linked to violence overall, but not specifically to firearm violence or mass shootings.

Researchers analyzed data from a sample of 4,550 individuals incarcerated for less than two years from the 2016 Survey of Prison Inmates, a large database of approximately 25,000 incarcerated adults.

The study, published in Justice Quarterly, is titled “Violence, Gun Violence and Mental Illness in a National Sample of Incarcerated Adults.” Mark Berg, professor in the Department of Sociology and Criminology and director of the UI Center for Social Science Innovation, led the study. Co-authors include Andrew Krajewski, Yi-Fang Lu, and Ethan Rogers.

“In short, mental illness differentiated individuals with histories of violence from those with histories of property offending, but it did not differentiate individuals with histories of gun violence from those involved in other forms of violence,” Berg said.

Mental illness and overall violence

The study first examined whether individuals with self-reported mental illness or diagnoses, such as depression, bipolar disorder, and schizophrenia, were more prone to committing violent offenses rather than non-violent ones.

Consistent with earlier research, the findings showed that people with mental illnesses were more likely to be involved in violent crime overall. The study found that individuals with a history of mental illness were more likely to report interpersonal violence (e.g., fights, physical assaults) than property crime (e.g., burglary, theft).

Mental illness, firearm violence, and mass shootings

However, unlike previous studies whose findings were mixed and based off a relatively small body of work, the study found no evidence that mental illness is linked to firearm violence compared to other types of violence, whether fatal or non-fatal. In doing so, Berg said, the study helps to clarify earlier results.

“Because firearms substantially increase the likelihood of injury and death in interpersonal disputes, the combination of elevated violence risk and firearm access may heighten the probability of lethal outcomes—even if mental illness itself does not specifically predict gun use,” he said.

In addition, people who carried out mass killings – defined as incidents with four or more victims – were no more likely to show signs of acute mental illness than those who did not commit such offenses. Substance use problems also didn’t set mass killers apart from other violent offenders.

Future directions for research

In the future, Berg said, researchers should investigate the same questions as this study but use additional measures of mental illness and different samples of both youth and adults.

“The essence of the issue assumes that mental illness has a unique relationship with gun violence perpetration, and some argue that this relationship is why the U.S. has such high levels of gun violence compared to our peer nations in the Western world,” he said. If so, then individuals burdened with acute mental illness should be at particular risk for gun violence – not just violence.”

What makes studying the connection between gun violence and mental illness difficult, Berg said, is that firearm violence is exceedingly rare in the general population, which means researchers need a study sample with sufficient variation in both mental illness and in crimes and acts of violence committed with and without firearms.

Study limitations

The study highlighted several study limitations including reliance on self-reported mental illness, and the lack of measures for specific symptoms (e.g., psychosis) that might influence violence.

Berg said, “It does not capture those individuals who choose not to report mental illness or who are not fully cognizant of their health profile to report their conditions.”

In addition, a prison-based sample may not generalize to the community. For example, incarcerated individuals may have different access to firearms or have a higher likelihood of committing a crime than those in the community.

“That the sample was high risk also means that the effects of mental illness on gun violence may be diluted or overwhelmed by other risk propensity factors in this population,” he said.