A new study points to a key way to reduce the prison population in the incarceration capital of the world: boost spending on public mental health.

Reducing the prison population means reducing jail expenditures. The average cost in the U.S. to incarcerate a person is $60 a day, an accompanying press release states.

As the ACLU has written, “The human and financial costs of mass incarceration are staggering.”

For the study, researchers Jangho Yoon and Jeff Luck, professors in the College of Public Health and Human Sciences at Oregon State University, analyzed data from 2001–2009 on 44 U.S. states and Washington, D.C.

They found that while greater spending on public inpatient care and greater spending on community mental health both decreased prison populations, the inpatient spending had a greater return on investment.

A 10 percent boost in per capita public inpatient mental health expenditure on average leads to a 1.5 percent reduction in jail inmates, they found.

“An increase in public inpatient spending would decrease jail populations in the 35 states that spend less than $134 per capita on community mental health care, and the District of Columbia, which also spends less than $134 per capita,” Yoon stated.

Under that amount, “the associated benefit-cost ratio is 26 cents, which indicates a positive intersystem return on investment of 26 percent. Every dollar spent annually on inpatient mental health by a state would yield a positive spillover benefit of a quarter dollar for the jail system by reducing the number of inmates,” he continued.