PRELIMINARY FINDINGS from Boston’s study of police-worn body cameras point to a small benefit in reducing citizen complaints filed against officers, but no impact on police use of force against civilians.

The mixed results of the study carried out by researchers at Northeastern University could prompt a fresh round of debate between advocates for body cameras and Mayor Marty Walsh, who has seemed skeptical of the idea of equipping all of the department’s 2,100 officers with cameras.

The pilot study, which involved 281 police officers who were randomly assigned to wear body cameras or serve as controls, found that the incidence of citizen complaints against police assigned to wear cameras was almost half that seen in officers serving as control subjects.

The overall number of complaints in both groups, however, was very small, with just 17 complaints recorded against officers wearing cameras and 29 complaints against control officers not equipped with cameras.

Boston Police Commissioner William Evans greets a resident in Dudley Square last July during one his regular neighborhood “peace walks.”

“In general, these analyses suggested that the placement of BWCs [body-worn cameras] on BPD officers seemed to reduce the incidence of citizen complaints,” wrote the researchers.

Reports of use of force by officers were not significantly different between the two groups.

A final report on the pilot study, including a broader look at the effect of body cameras on police-civilian interactions, is expected to be released in June.

“Nationwide, the impact of body cameras has been varied,” Police Commissioner William Evans said in a statement. “Waiting for the results of the full analysis is prudent and necessary to really understanding the context and setting in which body cameras may have the most impact.”

The researchers acknowledged that the study was limited by the small number officers taking part and the generally low rate of complaints against Boston officers and incidents of police use of force. “It is important to note here that the research design was not well positioned to detect an effect due to modest statistical power and low base rates for key outcomes,” they wrote.

Those rates were decreasing even in the years leading up to the study, with citizen complaints against Boston police officers down 44.7 percent from 360 cases in 2013 to 199 cases in 2016. Use of force reports by police dropped by a similar amount during this period, with reports down 43.9 percent from 107 incidents in 2013 to 60 in 2013.

Walsh did not offer a clear indication of how the preliminary results might shape his thinking on the issue.

“Boston has become a model for strong community policing and our goal is to continue building trust and positive relationships between residents and law enforcement,” he said in a statement. “Ultimately, we want to be sure that any investment in public safety supports this work and I look forward to learning more.”

The use of body cameras by officers has become a major issue in policing across the country in the wake of a number of high-profile cases of police use of deadly force against unarmed black civilians. The technology has been touted as a way to reduce such incidents as well as to reduce assaults against police.

A 2015 survey showed that 95 percent of big city police departments were using body cameras, intending use them, or implementing pilot studies evaluating their impact.

Despite the rush to embrace body cameras, the evidence on their effects is limited and not consistent.

The first controlled study of body cameras was completed only five years ago. That small study, carried out in Rialto, California, showed strong benefits in reducing citizen complaints against police and in officer use of force. A number of studies have been completed since then, not all of them showing clear benefits.

One of the larger studies, conducted among 2,000 officers in Washington, DC, reported in October that there were no clear benefit of body-worn cameras on citizen complaints, officer use of force, and other outcomes.

Walsh has twice publicly cited that study, once in a mayoral debate last fall and again last Friday in an appearance on WGBH radio. In his comments last week, Walsh mentioned the study and said he was “not convinced yet” of the case for equipping all 2,100 Boston police officers with cameras.

Segun Idowu, a leader of the Boston Police Camera Action Team, a community group advocating for body cameras, said he is concerned that Walsh has made up his mind against broad deployment of body cameras and “is just grasping at whatever pieces of information support that claim.” Idowu said the conversation should focus on how body cameras will be used, not on whether they will be used.

City Council President Andrea Campbell said with the results “demonstrating an overall positive response and a decrease in police misconduct reports, the question is, where do we go from here?”

Campbell, who chaired the council’s Public Safety Committee until winning the president’s post earlier this month, said full deployment of body cameras across the department may not be something that can be done immediately, even if there is agreement on their usefulness. “Given the price tag for this, we might want to consider implementation in phases,” she said. “I do think body cameras should be one tool, among many, that we use as part of a larger public safety strategy to improve interactions between officers and civilians and vice versa, to help address issues of violence, and to increase accountability for the police department.”

Rahsaan Hall, director of the racial justice program at the ACLU of Massachusetts, said in a statement that the organization is “pleased that the Boston Police Department reports that the body camera pilot program showed the cameras ‘may generate small benefits.’”

Hall said the ACLU believes body cameras “with appropriate privacy protocols can be an important step towards greater oversight and accountability of police officers.”

No one could be reached at the Boston Police Patrolmen’s Association for comment on the pilot results.

As modest as the study findings are, they offer considerably more reliable information than would have been available under the city’s original plan for a body camera pilot study.

The police department initially asked officers to volunteer to take part in a pilot study. When no officers stepped forward, Evans said he would assign officers to the study, a declaration that prompted a court challenge from the patrol officers’ union, which maintained that such a move would violate its contract with the city.

In September 2016, a Suffolk Superior Court judge sided with Evans and allowed the pilot program to move forward. The Northeastern research team, led by Anthony Braga, director of the university’s School of Criminology and Criminal Justice, designed a pilot study in which officers were assigned at random to wear cameras or serve as controls. That randomized study model, considered the gold standard in research design, allowed for a much more valid test of body cameras than would have been the case if officers volunteered for the pilot, since it’s likely that those who stepped forward on their own to wear body cameras would have differed in important ways from those not volunteering.