A study published in 2020 by the journal Criminology & Public Policy found that 60% of mass shooters who wantonly killed people in public settings from 1976 to 2018 "had been either diagnosed with a mental disorder or demonstrated signs of serious mental illness prior to the attack." In contrast, 4.6% of noninstitutionalized U.S. adults have a serious mental illness. The U.S. has one of the lowest rates of psychiatric institutionalization in the developed world, and from 1955 to around 2010, the portion of the U.S. population in public psychiatric hospitals declined by 96%. Per an academic book about "America's Mental Illness Crisis," "The magnitude of deinstitutionalization of the severely mentally ill qualifies it as one of the largest social experiments in American history."