or consonant with other forms of violence, thus providing clues about whether its causes were the same as those that caused other forms of violence.

We also needed to identify and read the literatures on violence that seemed related to the particular incidents of violence we had been asked to study. This was important not only in itself, but also as a necessary guide to our efforts to interpret the cases. Our theoretical understanding and review of data would help us select cases and construct the templates for gathering information. Our review and understanding of the relevant literature would help guide our interpretation of the cases.

At the outset, it was not clear which particular theoretical literature would be relevant, since we did not yet know how to locate the form of violence we had been assigned to study. Again, we knew it was at the tail of some distribution because the incidents were extremely serious and therefore quite rare. But it was by no means clear to what theoretical categories these particular instances of violence should be assigned.

In the end, we explored several literatures to help interpret the cases and more generally to help us think about what might be causing the incidents and how they might best be prevented. First, was a very small literature on incidents that looked very much like the ones we had been asked to review (only four studies, and only two of them that met reasonable standards of scientific care and rigor). Second, there are large literatures on broad categories of violence, such as violence in general, youth violence, school violence, and the relationship between violence and suicide. Third, there were also literatures on some specialized forms of violence that bore some similarity to the incidents under study. These included literatures on mass murders, rampage shootings, and “suicide by cop” (e.g., incidents in which individuals seemed to shoot in order to provoke a response by the police). Finally, because there might be some contagion effects in the events we were examining, we looked into the literatures that explored the contagiousness of violence and other social events.

These are the sources the committee used to understand the incidents of lethal school violence involving multiple victims: the cases that describe six specific incidents; a statistical database constructed for the committee’s purposes from several existing sources; and several literatures that had something more or less directly relevant to say about this phenomenon.

Perhaps the most valuable resource we had was the commitment and expertise of the case writers who developed the cases, all senior scholars with a significant amount of experience in qualitative methods and most with substantive knowledge in the area of youth violence. The discussions we held were designed to stretch the evidence and knowledge on incidents of lethal school violence as far as we reasonably could, and to



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