Nine months after the release of a report detailing a pattern of bias in police stops of blacks in Boston, the Boston Police Department has instituted new guidelines for its officers that explicitly prohibit stops based solely on race, gender or physical characteristics.

The new guidelines also reaffirm the requirement that officers give a specific reason for why drivers or pedestrians are stopped, questioned and/or patted down or searched. Last year’s police stops report found that officers most often used the vague explanation “investigate a person” as their reason for stopping individuals.

That study, released last October, found that blacks make up the majority of all police stops in the city, despite making up only 24 percent of the city’s population. While police officials said the disproportionate numbers of blacks being stopped correlated to higher crime and more gang activity in black neighborhoods, even when those factors are taken into account, blacks were stopped at a rate disproportionately higher than whites or Latinos.

An independent study examining the same data set as the October 2014 report – stops and searches conducted between 2007 and 2010 – revealed that white police officers are more likely than their black colleagues to stop, frisk and search people.

The study also showed that more than half the people stopped by police had no prior arrest records.

City Councilor Tito Jackson said he was pleased that the police department is instituting reforms.

“I think that when a report is done and you see data that shows a higher proportion of stops of blacks than whites, it’s important that you act,” he said. “It’s important that police provide a justification for stops and that people’s civil and constitutional rights are not violated.”

Civil rights advocates and black teens in Boston have long argued that police stops, as practiced by Boston police officers, violate the 4th Amendment’s protections against illegal search and seizure. Under U.S. law, police officers can only forcibly stop a civilian if they have a reasonable suspicion that the civilian has committed a crime or is about to do so.

A reasonable suspicion justifies a search and a pat-down for weapons, but not a search. Boston teens have long maintained that police routinely illegally stop and search them. Police are allowed to search a person’s pockets, bag or car only if they have probable cause to make an arrest.

BPD Commissioner William Evans told the Boston Globe that the department would begin issuing annual data on police stops. The most recent publicly-released police stops data are 2010 data that was included in the Oct. 2014 report, which were requested by the American Civil Liberties Union of Massachusetts and the BPD.

“The ACLU of Massachusetts is pleased to hear that the BPD will adopt some of the reforms we recommended in our October 2014 report, Black, Brown & Targeted, including a bias-free policing policy and regular publication of data,” wrote ACLU Massachusetts Executive Director Carol Rose in a blog. “But in light of the serious evidence of disparate treatment, we hope the BPD also will adopt additional reforms, such as using body-worn cameras with adequate privacy protections that have been adopted by other major-city police departments.”