Matching prisoners to jails: peer effects are of first order importance

 Akhil Vohra points me to this very interesting matching problem, which is apparently quite far from a good solution:

RIKERS ISLAND: City Jails Scrap Last Remnants of Pricey Consultant Plan as Deaths Mount BY  REUVEN BLAU, May 18, The City

"In 2018, the city Department of Correction began using a new detainee classification process created at great expense by consulting group McKinsey & Company. 

"The de Blasio administration had paid the white-shoe firm $27.5 million to create the system that used an algorithm based on a host of factors — including age, possible gang affiliation, and any prior history in jail — to determine where to house people behind bars with the least risk for confrontation. 

"On Tuesday, jail Commissioner Louis Molina announced that the pricey system — widely criticized for failing to reduce violence — will be formally scrapped after just four years as part of the department’s court-mandated overhaul plan. 

...

"jail officials have long struggled where to place new detainees to reduce the likelihood of fights. Top jail supervisors have traditionally tried to avoid creating housing units based on gang affiliation, according to current and former jail insiders. 

"Units made up of just one gang tend to get along with each other but also have the ability to gang up on the officers in the area and are more likely to join forces to ignore basic orders, jail experts say. 

"Housing units mixed with people from at least two different gangs as well as some people who are totally unaffiliated are considered the golden standard, according to criminologists. 

"But other factors are also important such as a person’s prior criminal history, age, and possible previous record in jail. 

...

"“It’s a revolving door of stupidity and poor decisions,” one high-ranking jail official, who spoke on condition of anonymity, told THE CITY. 

“We changed from that system because it wasn’t working, now we are reverting back to it,” the jail insider said. 

...

"Jail officials said the result was part of the chaos that has led to a massive spike in the number of stabbings and slashings among detainees and assaults on staff."