MASS MURDERS AND WOMEN MASS MURDERERS

Mass murders seem to be increasing in recent years with 2017 being the highest year (see figure) because of the Las Vegas Nevada incident.*  In addition, there were more than 20 shooting incidents in which at least three people were killed, including the Marjory Stoneman Douglas (FL), Santa Fe (TX)  High School shootings  But nearly all mass shootings are done by men.  The number of mass shootings by women is so rare that there are not enough cases to determine a reason.  I find it curious, however, that testosterone is not mentioned as a cause of the overwhelming mass shootings are by men.

(Click on figure to enlarge)

An FBI study of 160 “active shooter” incidents between 2000 and 2013 found that only 6 incidents, or 3.8%, were perpetrated by a female shooter. All six of these female shooters used handguns, according to the FBI study. **

Women in Mass Attacks
None of the perpetrators behind the 28 mass attacks in 2017 was female, according to a report by the US Secret Service. A study led by Lankford, published in the journal Violence and Victims, looked at 292 public mass shooters worldwide from 1966 to 2012 and found that only one of those was female.**

No Women in School Shootings
Status plays a large role in school shootings, a particularly male phenomenon, said Katherine Newman, a sociologist at the University of Massachusetts, Amherst. Newman, author of "Rampage: The Social Roots of School Shootings" (Basic Books, 2005), argues that there has never been a typical school shooting with a female perpetrator. A case in San Diego in 1979 involved a teenage girl who lived across from an elementary school and started shooting children and staff from her home one morning. But in cases of random shootings on school grounds by a person who is part of that school's community, the perpetrators are all male, Newman told Live Science.

For a list of mass shootings by gender, see the article from Statistica.****  States with the most murders were California (1830), Texas, Florida, and Pennsylvania (997), in declining order.****

Note added August 4, 2019:  After publishing the above just yesterday (August 3rd), I heard that there was a mass shooting in El Paso, TX, at a Walmart with today's report that 20 are dead and 26 wounded.  A 21-yr old white male has been taken into custody.
(https://www.cnbc.com/2019/08/04/9-killed-at-least-16-injured-in-ohio-shooting-suspect-dead.html)
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This morning (August 4th) in the news is a mass shooting in Dayton, OH, with nine dead.  The gunman was wearing body armor and a mask and was using a .223-caliber, AR-15 type, rifle with a100 round magazine.  News is that at least 26 others are being treated at hospitals (including some with sprained ankles and bruises from the stampede).  The  24 yr-old white male was killed.  His motive is unknown.
(https://www.cnbc.com/2019/08/04/9-killed-at-least-16-injured-in-ohio-shooting-suspect-dead.html)

Sunday's shooting in Dayton is the 22nd mass killing of 2019 in the U.S., according to the AP/USA Today/Northeastern University mass murder database that tracks homicides where four or more people killed — not including the offender. The 20 mass killings in the U.S. in 2019 that preceded this weekend claimed 96 lives.
(https://www.newsmax.com/newsfront/dayton-ohio-mass-shooting-9/2019/08/04/id/927171/?ns_mail_uid=142cf6cb-b757-4a77-afda-d3310b9288ee&ns_mail_job=DM43006_08042019&s=acs&dkt_nbr=010102uzbq03)

Note added August 6, 2019:  Two more of the injured people in the ElPaso, TX, shooting have died bringing the total to 22 dead.
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It should be mentioned that there was also a shooting at the Gilroy, CA, Garlic Festival on July 28 by a 19 yr-old gunman wearing a bulletproof vest, within a week of the El Pal shooting.  At Gilroy, four people were killed, including the gunman, and 17 injured.

* https://everytownresearch.org/reports/mass-shootings-analysis/
** https://www.cnn.com/2019/05/08/health/female-shooters-rare/index.html
https://www.theguardian.com/technology/2018/apr/04/youtube-shooting-gun-attacks-in-the-us-are-rarely-carried-out-by-women
https://time.com/5227473/female-mass-shooters-rare-fbi-study/
*** https://www.livescience.com/53047-why-female-mass-shooters-are-rare.html
 https://www.statista.com/statistics/195331/number-of-murders-in-the-us-by-state/
**** https://www.fbi.gov/file-repository/active-shooter-incidents-2000-2018.pdf/view
 https://www.statista.com/statistics/195331/number-of-murders-in-the-us-by-state/

Some articles on Testosterone
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3693622/
https://www.psychologytoday.com/us/blog/the-human-beast/200907/sex-hormones-and-womanly-passions