In January, a burst of gunfire killed a 24-year-old man and wounded three others as they sat in a car in Roxbury.

Later that month, six people were injured in a shooting at a birthday party at a community center in Jamaica Plain.

And over Thanksgiving weekend, an MBTA conductor was killed and three other men were injured in a shooting outside of a Fenway bar.

Those are just three of the six mass shootings that have taken place in Massachusetts so far this year, according to the widely cited Mass Shooting Tracker, a site maintained by Reddit users from the Guns Are Cool forum who have attempted to chronicle every incident in which four or more people were shot since 2013.

According to the tracker, there have been more than 350 mass shootings across the U.S. this year.

The FBI, by contrast, defines a mass murder as an incident in which four or more people are killed. Several media outlets have cited that mass shooting statistic as a stark example of America’s gun violence problem in the days since a married couple killed 14 people and shot 21 others in San Bernardino, California on Wednesday.

But experts like Northeastern University criminology professor James Alan Fox, author of Extreme Killing, say this new definition of a mass shooting is overly broad and misleading because it combines disparate shooting incidents into one group.

“There’s a big difference between mass shootings and mass killings,” he said. “They roll out those numbers when there’s a mass killing ... [and] the reader makes the translation that mass shootings are what happened [in San Bernardino].”

“Four people killed is very different than four people injured,” Fox said. “Why combine them all in one part?”

Boston Police spokesman Lt. Michael McCarthy cautioned against putting San Bernardino-style attacks in the same category as the three “mass shootings” in Boston this year, all of which were related to gang violence, he said.

“[These are] instances where you have an incident with a beef with another person, and their intended target may be standing with three people, and they have no regard for those around or behind,” McCarthy said.

McCarthy said these shootings into crowds followed the “law of averages.” The more people there are nearby, the higher the chances that more will be hit by stray gunfire, he said.

See, for example, the shooting on Thanksgiving outside a Fenway bar. The one person killed in that shooting, MBTA conductor Jephthe Chery, was described by police as “an innocent” who was caught up in crossfire.

Locally, Massachusetts saw a slight increase in violence according to the Mass Shooting Tracker: one in 2013, four in 2014, and six this year.

Yet these violent incidents bear little resemblance to how many Americans imagine a mass shooting.

“Four people killed is very different than four people injured. Why combine them all in one part?” Fox said. “The outcome matters.”

Fox also criticized the lack of benchmarks or historical comparisons at Mass Shooting Tracker, which has only existed for three years.

“There’s no trend,” he said. “You can’t say it’s higher than it used to be. It could be lower. We don’t know.”

Though mass shootings appear to be featured more prominently in recent years, there’s not much evidence they happen more often. A Congressional Research Service analysis of fatal mass shootings, in which four or more people are shot and killed, found that there were about 21 such incidents per year from 1999-2013. [PDF]

The graph above fluctuates from year to year without a clear trend, especially given population increases.

“There’s no pattern there,” Fox said. “It’s random fluctuations.”

The emphasis on these mass shootings also ignores the dramatic decrease in violent crime over the past two decades across the U.S. Homicides and shooting incidents are down in Boston again this year compared to last, McCarthy said, with homicides at a 15-year low.

While the FBI is investigating the San Bernardino attacks as terrorism, McCarthy said Boston police don’t treat the local shootings of four or more people shot any differently from other investigations.

“It’s unfortunate that these incidents happen, but they’re handled the same way we handle every shooting, whether it’s one victim or several victims,” he said.

Gallery: Images from the shooting in San Bernardino: