Frequently Asked Questions

How do you define “mass shooting”?

We define a mass shooting to be an incident of violence in which 4 or more people are shot. We do not consider the motive of the shooter, or whether he or she shot up a school, workplace or street corner. Our mission is to record all incidents of mass gun violence. We include the shooter's death because suicide matters and means matter. Ignoring the shooter's death is not logically consistent with research that tracks the death toll of firearm suicides in our society.

The RAND corporation has a great discussion of mass shootings and the challenges of categorizing them here.

Isn't that the same as “mass murder”?

No, the current FBI definition of mass murder, from their recent study of active shooter events, is three or more killed: “the federal definition of ’mass killing’ — defined as ’three or more’ killed“ (source, PDF, pg 7).

The FBI does not define mass shooting. We differentiate between the two largely because of the huge variable that medical care represents. A mass shooting 50 miles from the nearest trauma center is much more likely to become a mass murder than one within 5 miles of the nearest trauma center. We use four people shot because that is more congruent with the colloquial definition of mass murder (four or more killed).

Aren't you people biased?

We make no secret of the fact that we are a strongly opinionated group of people. Most of us support gun control. However, we believe that the best way to make our case is to present facts as objectively as possible. We believe that we do not need to distort, because the data is on our side. This is why pro gun members of congress have been so eager to prevent government agencies from researching gun violence. We seek to produce the best possible data, to do otherwise would be a waste of our time.

I heard you included a BB gun shooting in your count.

At one point there were a few BB gun shootings included in the data set since the CDC tracks BB gun shootings that require an emergency room visit and considers them to be a type of shooting. However the decision was made to remove them from our database since they caused confusion. These represented 3 cases, less than 0.3% of our data.

I found a mistake in your data. That means all your data is suspect, right?

No. This is an unfunded, crowd-sourced effort, which means errors can and will be introduced. We are transparent with our data and we strive to achieve the highest degree of accuracy possible. If you see an error, please message the mods at GRC and we will review the entry. We do remove entries if they are found to be faulty (occasionally the media will report 4 people shot when it was 3 shot and one injured when someone else ran away from the shooter and knocked them down, for instance).

What we do know is that this dataset represents at least the minimum number of mass shootings that have happened. There are almost certainly a few that we missed or didn't get written up by the news.

Why should people trust crowd-sourced data?

Until Congress starts funding gun violence research, others will have to fill the void. At this point (December 2015) Congress has effectively blocked the CDC from researching the underlying causes of gun violence. Our volunteers include published researchers with experience in scientific and medical fields, who understand how to collect and interpret data. We are confident in our data and we welcome anyone to review it.

How can I get involved?

We are working on tools to allow more people to participate in collecting more and better data. Start by joining our subreddit or follow us on twitter at @MassShootingTrk.