Today’s horrific tragedy will undoubtedly spawn another round of news stories saying that this is the “Nth Mass Shooting,” or “it’s been N days since the last Mass Shooting in the U.S.” But many of them will give completely different numbers.

When it comes to mass shootings, it can be hard to find good data—in part because in 1996 congress essentially defunded the Center for Disease Control’s research into gun violence, and in part because there is no standard definition of a mass shooting. But that doesn’t stop people from keeping count—at least five organizations track mass shootings, and this attack would not qualify as a mass shooting according to Mother Jones, or USA Today’s records of Mass Shootings.

How is this possible? How can a doctor walking into a hospital with an AR-15 and shooting seven people then shooting himself not be counted as a “mass shooting?” In part, because it took place in a hospital.

See, many of the organizations that track shootings only count shootings where 3-4 died from the shooting. So as the NY Times noted, “Some believed that the death toll would have been far higher had the shooting occurred anywhere but where it did — a hospital filled with state-of-the-art medical equipment, and with doctors and nurses who rushed to victims and performed triage where they fell, in staircases and hallways, even as the gunman was still at large.”

While deaths are clearly the most tragic outcome of a shooting, whether or not a shot was deadly does not change the motivation for the incident. In determining a mass shooting sn’t the number we care about the number that were shot at, not the number injured or dead? Why is it important shooter hit or missed their target when classifying a shooting as a mass shooting? In fact, some researchers suggest that improved treatment of gunshot wounds and the use of gun deaths as a metric has decreased our attention to the fact that gun violence appears to be rising.

But expedient medical care isn’t the only reason this shooting won’t be classified as a mass shooting according to some lists. For example it probably wouldn’t make the FBI Active Shooter Report, which only count shootings that occurred in public areas, since the victims were doctors and medical students it may be counted as a workplace dispute  as opposed to a mass shooting that occurred in a public space.

In fact the only two organizations I could find that would definitely count this incident as a mass shooting are both crowd-sourced projects that operate online: the Mass Shooting Tracker and Gun Violence Archive.

If one is concerned with general gun violence, the Mass Shooting Tracker, Gun Violence Archive, or USA Today’s mass shootings, which ignore location and motivation, may provide the most comprehensive data. However, many of the incidents they count such as gang fights or familial murder-suicides aren’t what we are typically referring to when we say ‘mass shooting.’ So if one is concerned with the seemingly random, public mass shootings other sources may be better better.

And how we classify these events is extremely important if we want to study them and figure out how to stop them.

Today’s story stands out more than normal to me, probably because the friends I entered medical school with just finished their first year of residency, and maybe a bit more because I’m living in New York.

Any shooting, mass shooting or not is tragic, and it’s important to remember that while guns are a major public health problem in America — particularly because of their use to commit suicide — mass shootings remain a rare cause of injury or death. How rare? Well, it all depends who you ask.