PITTSBURGH — A multi-year study shows Pittsburgh police are using force less frequently when making arrests but still using more force in arresting black suspects, although that frequency is going down, too.

The report, released Thursday by Chief Cameron McLay, recommends further study of several questions, including whether officers encounter more resistance from black suspects and are, therefore, justified in using force more frequently.

“Are these differences in the degree of resistance by the subjects and/or differences in how police respond at the earliest sign of resistance?” the report asks in a section entitled “Areas of inquiry.”

The city has been tracking the use of force by officers since it entered a consent decree in 1997 with the U.S. Department of Justice, designed to lower instances of police brutality. Federal overseers have since determined the city improved its policies and practices and their oversight ended in 2002.

Still, Pittsburgh continued to collect statistics through so-called Subject Resistance Reports, which officers must file whenever they use force to control or arrest someone. The latest study crunched numbers from 2010 through 2015 from these reports.

The study shows about 760 of the city’s 900 officers used force no more than five times between 2010 and 2015, though 120 officers used force at least 25 times during that same period. Overall, police used force in about four-tenths of 1 percent of all incidents, or about 1,500 of the 360,000 calls police handle annually. Not surprisingly, the reports show officers use force more frequently — about 10 percent of the time — when someone is arrested, the study found.

But the study also shows officers used force at greater frequencies in arresting blacks than non-blacks. Police used force in arresting blacks 10 percent more often last year, even after the statistics were adjusted for the number of arrests involving blacks and non-blacks. The disparity was 20 percent in 2010, the first year of the study, and as high as 31 percent in 2012, McLay said.

Mayor Bill Peduto hired McLay, who is white, in 2014 after McLay established a reputation as a reform-minded police captain in Madison, Wisconsin. McLay promised to use statistics to drive reform in Pittsburgh.

McLay succeeded Nathan Harper, who is black and was hired as a patrolman in 1977 and rose through the ranks to become chief in 2006 under Peduto’s predecessor, Luke Ravenstahl.

Harper resigned in 2013 before pleading guilty and receiving 18 months in federal prison for wrongly spending nearly $32,000 on personal expenses from an off-the-books police slush fund.

McLay has sparred with police union leadership by tweeting concerns about racial bias among police, and has fired one officer, Stephen Matakovich, with a reputation for using too much force. Matakovich was a 22-year veteran sergeant. He’s now awaiting separate trials on city police and FBI charges that he wrongly pushed and punched a drunken fan at a championship high school football game last November. He has denied wrongdoing.

Matakovich and the fan, who is also suing the city, are both white.