More or less the same results as Matt - 95% CI upper limit every
~5months.  More important though is what we can expect to occur, which is
every 30 days during the school year.

Mass shooting definition:  shooting resulting in at least 3 victims,
excluding the perpetrator (per definition of the Investigative Assistance
for Violent Crimes Act of 2012, signed into law on Jan 2013)

SPC T chart of days between mass school shootings (n=121), last 100 years
(Upper Control Limit = 3SD); not adjusted for population growth or
seasonality; CL = average of 1 every 113 days

[image: Inline image 1]

The most recent period of stability goes back from event #86 in the figure
above, starting at the beginning of 2013 until the current date. This time
period makes a new T chart below, which is stable (no significant change)
by all special cause rules (1 point >3SD from the center line, 9 points in
a row on same side of center line, 6 points in a row all increasing or
decreasing, 2 of 3 points >2 SD on same side from CL, 3 of 4 points >1 SD
on same side of CL). Now, there is 1 every 41 days, with 3SD UCL of 271
days; not adjusted for seasonality, population growth, or transformed for
normality). To the original question of 95% CI question, the UCL for 2 SD
is 170 days. The good news is that this is a stable process, so the effect
of interventions could be associated with changes in the outcomes.  The bad
news is that this is a stable process.

[image: Inline image 7]

But kids are in school seasonally - with decreases seen in spring break and
summer. So when school's in session, it's probably more like one mass
shooting every 30 days.

[image: Inline image 3]

If you expand the criteria from school mass shooting to any school shooting
(at least 1 injury or death), January is the most frequent month for any
school shooting.

[image: Inline image 4]

Implications: Mass shooter drills in September?  Increase mental health
resources/screenings in schools/staff/communities after winter break? Other
ideas with likely bipartisan support?

Long road ahead...


Paul Mullan, MD, MPH
Director of Research and Quality Improvement, Division of Emergency Medicine
Children's Hospital of the King's Daughters
Associate Professor, Eastern Virginia Medical School
Cell: (713) 855-4827. Office: (757) 668-9220
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