An advocacy group that supports stricter gun laws says the shooting that killed 17 people at a Florida high school on Wednesday was the 17th incident of gunfire at a U.S. school so far this year. Of the 17 incidents, one was a suicide, two involved active shooters who killed students, two involved people killed in arguments and three involved people who were shot but survived. Nine involved no injuries at all. Some questions and answers about how different groups define a school shooting:

WHAT IS THE EVERYTOWN FOR GUN SAFETY ORGANIZATION AND WHAT DEFINITION DOES IT USE?

Everytown for Gun Safety is an advocacy group that supports stricter gun laws. It is backed by billionaire and former New York City Mayor Michael Bloomberg. Everytown's website says it defines a school shooting as any time a firearm discharges a live round inside a school building or on a school campus or grounds, as documented by news reports or police.

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WHAT CRITERIA DO OTHER GROUPS USE?

Gun Violence Archive, a not-for-profit corporation that collects information about gun-related violence in the United States, defines a school shooting as one happening on the property of an elementary school, secondary school or college campus during school hours or during extracurricular activities.

The Centers for Disease Control and Prevention's National Center for Injury Prevention and Control does not have a definition specific to school shooting, but does have a definition for "school-associated violent deaths" (SAVD), spokeswoman Courtney N. Lenard says. The center defines an SAVD as "a homicide, suicide, or legal intervention in which the fatal injury occurred 1) on the campus of a functioning public or private elementary or secondary school in the United States, 2) while the victim was on the way to or from regular sessions at such a school, or 3) while the victim was attending or traveling to or from an official school-sponsored event. Cases include deaths of students as well as non-students (e.g., faculty, school staff, family members, or community residents)."

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HOW MANY PEOPLE HAVE DIED IN SCHOOL SHOOTINGS THIS YEAR?

Twenty-one have died, including 17 at Douglas Stoneman High School in Parkland, Florida. A North Carolina college student was shot to death during a fight at Wake Forest University on Jan. 20. A 15-year-old fatally shot two classmates at Marshall County High School in Kentucky on Jan. 23. And a 32-year-old man was fatally shot outside a high school basketball game in Philadelphia on Jan. 31.

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WHAT ISN'T COUNTED ON THE EVERYTOWN LIST?

Everytown doesn't count incidents in which guns were brought into schools but not discharged, or where a gun was discharged off school grounds. The group has removed one suicide from its 2018 list of shootings. It occurred outside a closed school.

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