On Saturday night, a 45-year-old man shot and killed six people and injured two others in and around Kalamazoo, Mich., authorities say. According to the crowd-sourced Mass Shooting Tracker, that act was the 24th mass shooting in the United States during the first 21 days of February and the 42nd mass shooting overall in 2016.

Mass shootings, defined as instances in which four or more people (which can include the gunman) are shot and killed or injured, have so far taken 62 lives and injured 142 people. The pace of mass shootings in 2016 is up slightly since last year, when there had been 34 such shootings by Feb. 21.

There are many ways that researchers and authorities define "mass shooting." The Gun Violence Archive excludes the shooter from the tally of injured and killed. By that definition, there have been 27 mass shootings this year. A shooting tracker by Mother Jones magazine uses more restrictive criteria, only counting shootings that have occurred in public places.

WATCH: 374 mass shootings in 365 days in one extraordinary graphic (Gillian Brockell, Julio Negron/The Washington Post)

There are strong arguments in favor of each of the definitions, depending on exactly which facet of the gun violence phenomenon you want to measure. The argument in favor of the Mass Shooting Tracker data above is that its the most comprehensive measure of multiple-casualty shooting events.

“If we're trying to capture true gun violence in our country, a broader definition [of mass shooting] is probably more useful than a narrow one,” Jim Bueermann, a former police chief in Redlands, Calif., told me last year.

For every terrible incident like the Kalamazoo shooting that make national headlines, dozens of other horrific tragedies fly under the radar. In Chesapeake, Virginia late last month, a man killed five members of his family before turning the gun on himself. In Texas earlier this month, a teenager shot and killed his mother and two neighbors before turning the gun on himself. A week before that, three people were killed and five more injured at a shooting at a house party in Glendale Arizona.

Since the Mass Shooting Tracker came into existence in 2013, there have been 1,077 mass shootings in the United States. The tracker's website also counts the days since the last mass shooting incident in the U.S. As of this morning, that number stands at zero.

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