WASHINGTON — District of Columbia police officers wearing body cameras reported using force about as often as colleagues who didn’t have them, and citizen complaints against the two groups were about even, according to a new study that bucks early expectations about the impact of the devices.

When the cameras started to appear in police departments in 2014, experts predicted behavior on both sides of the badge would improve under the watchful eye of the lens. But the look by Washington’s in-house research branch suggests otherwise – a finding that could shift the debate on one argument used to put the cameras in virtually every big city police department nationwide.

D.C. Police Chief Peter Newsham said the results surprised department leaders and were “not what we anticipated.” He said that it appears in many police interactions, “cameras didn’t make a difference.”

The chief said the recordings have been a valuable tool, providing a precise record of tense and difficult encounters, including police shootings.

Washington says the study of its $5.1 million program is among the more comprehensive looks at whether police-worn cameras affect behavior by officers and the people they encounter.

Police body cameras became seen as a key tool for reform after growing concern over the deaths in several cities of people in police custody. Public officials quickly heeded calls to infuse new levels of public accountability and transparency into everyday police work.

Though some police departments were reluctant, most contended the videos would most often exonerate officers facing allegations of misconduct, provide the public with a unique perspective of officer’s work and be an invaluable tool for training. D.C. police, and the labor union, embraced the program.

The D.C. research looked at a period where the police force was rolling out its body camera program – and some officers had the cameras while others were still waiting.

Researchers found that slightly more officers with cameras reported using force than those without. And more people filed complaints against officers wearing cameras than without. The research team said the differences were statistically insignificant, making the influence of the cameras a wash.

Police agencies “should not expect dramatic reductions in the use of force complaints, or other large-scale shifts in police behavior solely from the deployment of this technology,” concluded David Yokum, who directs The Lab @ DC, which conducted the study with assistance from outside universities.

In an interview, Yokum added, “So if you are a police department thinking that this technology on its own is going to be something to cause big shifts on those two dynamics, this would be a cause to recalibrate your expectations.”

Newsham, the chief, said the biggest benefit of cameras has been having a clear record in controversial incidents, such as a Dec. 25, 2016, fatal police shooting of a man during a domestic dispute. Relatives argued police shot an unarmed man; the body camera video showed the man with “a rather large butcher’s knife,” Newsham said. “In today’s environment in policing, having legitimacy is something we have to have.”