By Christine Vestal, Stateline

A panel of mental health and law enforcement experts has estimated that roughly one-third of acts of mass violence — defined as crimes in which four or more people were killed — since the 1990s were committed by people with a serious mental illness.

However, the study emphasized that people with serious mental illness are responsible for less than 4% of all the violent acts committed in the United States. Mass shootings accounted for less than two-tenths of 1% of U.S. homicides between 2000 and 2016.

The estimates came in a study released Tuesday — Mass Violence in America: Causes, Impacts and Solutions — by the National Council for Behavioral Health. To reduce the number of violent acts, the panel endorsed “red flag” laws enacted in at least 17 states that provide a way to remove guns from people who pose an imminent threat to themselves or others.

The research and advocacy group also recommended the creation of threat assessment teams within local communities, schools and other organizations that include professionals from the fields of human resources, law enforcement, law, security and behavioral health.

In addition to shedding light on the connection between mental illness and mass violence, Chuck Ingoglia, president and CEO of the National Council, said the report was intended to provide a community-wide solution to reducing it.

“For many law enforcement officers, clinicians, teachers and others, a lack of knowledge has prevented them from developing a coordinated plan to prevent mass violence. Previously, we have done our best to prepare for the aftermath. With this comprehensive plan, we finally have a roadmap to preventing and reducing it.”

Until now, there has been no standard statistic on the connection between mental illness and multiple killings. Instead, a series of studies have estimated the percentage of mass violence involving a person with mental illness to be from 5% to more than 70%, depending on the definition of mental illness used, as well as the definition of mass violence.

In the aftermath of last weekend’s shootings in Texas and Ohio, the National Alliance on Mental Illness said in a statement, “Every time we experience a tragedy like this, people with mental illness are drawn into the conversation.

The truth is that the vast majority of violence is not perpetrated by people with mental illness. Statements to the contrary only serve to perpetuate stigma and distract from the real issues. NAMI sees gun violence as a national public health crisis that impacts everyone.”

More than half of all Americans will be diagnosed with a mental illness or disorder at some time in their life, according to the Centers for Disease Control and Prevention. In a given year, 1 in 5 U.S. residents will experience a mental illness. And 1 in 25 live with a serious mental illness, including schizophrenia, bipolar disorder or major depression, according to the agency.

Stateline is an initiative of The Pew Charitable Trusts that provides daily reporting and analysis on trends in state policy. Since its founding in 1998, Stateline has maintained a commitment to the highest standards of non-partisanship, objectivity, and integrity. Its team of veteran journalists combines original reporting with a roundup of the latest news from sources around the country. Stateline focuses on four topics that are key to state policy: fiscal and economic issues, health care, demographics, and the business of government.