NBC News
Police have said so for years and now scientists have measured the
effect: Mass shootings and school attacks do inspire copycats.
As many as 20 to 30 percent of attacks are set
off by other attacks, according to researchers at Arizona State
University and Northeastern Illinois University. The effect lasts about
13 days, they write in the report published Thursday in the Public Library of Science journal PLoS ONE.
And mass killings — such as the 2012 attack on small children at Sandy Hook elementary school in Connecticut, the 1999 Columbine massacre, and last month's shooting of nine people at a prayer meeting in Charleston — are becoming alarmingly common in the United States.
"On average, mass killings involving firearms
occur approximately every two weeks in the U.S., while school shootings
occur on average monthly," wrote Sherry Towers, a research professor at
ASU, and her colleagues.
Such attacks are more common in states where more people own guns, they added in their report.
"Statistics are not readily available on the
incidence of mass killings and school shootings in other industrialized
countries, however studies have shown that the firearm homicide and
suicide rates in the U.S. are several times higher than that of any
other industrialized country and the patterns appear to be due to higher
rates of firearm ownership in the U.S. compared with other
industrialized countries," they wrote.