The de Blasio administration paid the consulting firm McKinsey & Company $27.5 million for a report about violence at the city’s Rikers Island jail complex that was allegedly filled with false data, according to a new investigative article.

McKinsey delivered a confidential report to City Hall in April 2017 that claimed the firm’s anti-violence strategies were responsible for a 50% reduction in violence in special Rikers housing units called “Restart” facilities, according to the news site ProPublica.

“The number was bogus,” ProPublica reports. McKinsey used inflated baseline statistics to make the decline seem greater than it actually was and cherry-picked model inmates for the Restart units.

“One email, forwarded to several consultants and obtained by ProPublica, shows a jail guard carefully curating the gang members on McKinsey’s initial list.

“One inmate was a Blood ‘but acceptable for program,'” the guard wrote. The two other gang members on the list — a Latin King and a Crip — were “not acceptable,’” the article says.

The consultants also gave nicknames for inmates lifted from Martin Scorsese’s “Gangs of New York.”

When fights broke out in the Restart units Rikers officials banned inmates considered most dangerous based on their ages, 18-21, from the facilities to drive the numbers down, the article says.

The McKinsey report was also riddled with data errors and made recommendations including the use of “aggressive dogs” that counter de Blasio’s plan to make Rikers more humane.

Since McKinsey began its work, violence across all sections of Rikers has nearly doubled, ProPulica reports.

De Blasio hired the firm — even though it had no experience with corrections issues — to stave off the appointment of a federal monitor and create “political cover,” according to ProPublica.

A McKinsey spokesman defended the firm’s work to ProPublica.

“The Restart program had a significantly positive impact in the housing areas of the jails in which the program was piloted,” he said. “These units experienced substantial reductions in violence as measured against comparably classified inmate populations.”

The spokesman denied that McKinsey’s consultants were involved in or aware of efforts to “improperly skew or reduce the reported levels of violence in the Restarts.”

A mayor’s office spokeswoman, Avery Cohen, told the site that the decision to hire McKinsey was sound and denied that city officials were involved in manipulating Restart units. “We sought the help of an outside firm for a singular purpose: to reduce the level of violence against staff and inmates and improve the safety of our overall facilities,” Cohen wrote in a statement. “We stand by the reduced rates of violence we saw in our Restart Units.”

Yet former Department of Correction Commissioner Joseph Ponte, who served during the time of the McKinsey consultancy, admitted in a 2018 deposition that his agency hand-picked “docile inmates” to manipulate the statistics, the report said.

“We did that, so that wasn’t news,” Ponte said in the deposition according to ProPublica.

“I was well aware of how we were selecting inmates in the Restarts — very carefully. It was a new process for us, and we wanted it to be successful,” he said.

McKinsey and corrections officials used an app called Wicker that automatically deletes message to communicate, in an attempt to avoid accountability, according to ProPublica.

One of the 36 people interviewed by the news outlet said a senior McKinsey partner, Anish Melwani, told some of his consultants that they’d “gone native” when they suggested beating inmates to quell inmate assaults.

Over $5 million was spent on data analytics software that was inaccessible in many cellblocks and froze the department’s IT system, ProPublica found.

A year after the report to reform Rikers was delivered, the mayor announced his plans to shutter the island facility.

When asked about the ProPublica report by The Post Cohen said: “We stand by the reduced rates of violence we saw in our Restart Units. There was never any attempt by City Officials to misrepresent or misconstrue these numbers.”

A rep for McKinsey also defended their report when reached by The Post.

“We stand behind our team’s professionalism and integrity, and the results of their work. The methodology used to measure impact was analytically sound. We did not improperly skew or reduce the reported levels of violence in the Restarts. We know of no efforts to do so,” McKinsey spokesman DJ Carella told The Post.