An Agent-Based Explanation for 20th Century Living Situation Changes in America’s Severely and Persistently Mentally Ill Population


The largest public mental health facility in the United States is not a hospital; it is the Los Angeles County Jail. This paper describes an agent-based approach to explaining why prisons and jails house so many of America’s most seriously mentally ill. It traces this fact to the differing ways in which various housing situations react to mental illness and to legislation passed in the 1960’s, which allocated public funding away from state mental hospitals.


A SPMI patient is generally defined as someone with a diagnosis of Schizophrenia, Bipolar Disorder or Major Depressive Disorder, and the group constitutes about 1.7% of the US population.6 The housing environment of the SPMI population in the United States has changed drastically over the past 60 years, most notably in the percentage of the population living in jail/prison versus the percentage living in community based care and private residences.

SPMI Housing Situation Changes