School shootings and mass killings sometimes seem to be spreading across America like a disease. Now, a mathematical analysis of hundreds of past events suggests a disturbing explanation: such high-impact violence may actually be contagious.
Based on multiple data sets spanning events from 1998 to 2013, scientists tracked the timing of mass killings and shootings in the United States. They found that between 20 to 30 percent of mass killings—attacks that cause four or more deaths—seem to happen in bunches that mirror the outbreak of a contagious disease.
A few killers actively admit to being influenced by previous murderers, like several school shooters who referenced the 1999 Columbine High School massacre as a factor in their later acts. Sociologists have long suspected that such a link may exist in a considerable number of cases, but it's been difficult to tell for sure whether murderers were inspired by others—especially when many commit suicide. So Sherry Towers of Arizona State University and her colleagues set out to try to quantify the effect on a large scale for the first time.
No comprehensive federal database yet exists on mass killings—though Towers stresses that one is desperately needed—so her team mined other sources of information. The Brady Campaign to Prevent Gun Violence compiled data on 188 school shootings from 1998 to 2013, and on 477 mass shootings (three or more shooting victims but not necessarily deaths) from 2005 to 2013.
To examine mass killings (those with four or more deaths) the researchers used data compiled in a USA Today study that found 232 incidents between 2006 and 2013. The data set was based on reports to the FBI but also on records at local police departments, which often aren't sent to federal authorities. The USA Today report highlighted many omissions and inaccuracies in the reporting of such crimes, so Towers and her team only included data they could verify.
When reviewed as a whole, the combined data revealed that mass killings and school shootings do appear to create a contagious period that lasts about two weeks, during which time similar crimes are more likely to occur, the team reports this week in PLOS ONE. Previous research suggests that other types of crime and violence may also be contagious. It appears that suicides, for example, can sometimes cause other vulnerable people to take their own lives.
“In many big cities they don't publish much information about suicides that might occur on a bridge, for instance, because it's been noticed that suicide can be contagious, so they don't give them a lot of coverage to try to help suppress that,” Towers notes.
The authors believe that nonstop news coverage of high-profile killings and the people who perpetrate them likely plays a role in any contagion effect that does exist. Details of these events more easily reach the relatively small number of people disturbed enough to consider committing more, the authors note. This idea is supported by the fact that contagion doesn't appear to exist for crimes that don't get as much national attention. The team's examination of mass shootings involving three or more victims but not necessarily any deaths found no evidence of contagion.
“We found that those events were so common that they rarely made it past the local news,” Towers explains. “So we theorize that's why we found no statistical evidence for contagion in that data set. It's not a large number of people who would do these things, it's very few people, so the local coverage just doesn't reach a big enough pool of people. I think it may be that only the national coverage is able to reach enough people.”
Media coverage is far from the only factor involved, Towers stresses. Clearly mental health issues play a major role. And according to the study data, access to guns does as well. “One other thing that popped out is that incidents are a lot higher in states that have a high prevalence of firearm ownership,” Towers says. “That appears to be playing a role. You get somebody who is emotionally or mentally distressed, then they also have access to weaponry, and it's a bad combination.”
"""Mashambulizi ya shule na mauaji ya watu wengi wakati mwingine yanaonekana kuenea kote Marekani kama ugonjwa." Uchambuzi wa hesabu wa matukio ya zamani unaonyesha kwamba jeuri ya aina hiyo inaweza kuambukiza. Kwa kutumia data kutoka miaka ya 1998 hadi 2013, wanasayansi wamegundua kwamba watu wengi waliuawa kwa kupigwa risasi nchini Marekani. Watafiti walipata kwamba kati ya asilimia 20 hadi 30 ya mauaji ya watu wengi - mashambulizi ambayo husababisha vifo vinne au zaidi - yanaonekana kutokea katika makundi ambayo yanaonyesha mlipuko wa ugonjwa wa kuambukiza. Wauaji wachache wanakubali kuwa wameathiriwa na wauaji wa zamani, kama vile wauaji kadhaa wa shule ambao walirejelea mauaji ya shule ya sekondari ya Columbine ya 1999 kama sababu katika vitendo vyao vya baadaye. Wataalamu wa jamii wamedhani kwa muda mrefu kwamba uhusiano kama huo unaweza kuwepo katika idadi kubwa ya kesi, lakini imekuwa vigumu kusema kwa uhakika kama wauaji walichochewa na wengine - haswa wakati wengi wanajiua. Sherry Towers, Mtaalamu wa Utafiti wa Utafiti wa Chuo Kikuu cha Arizona, na wenzake walianza kufanya utafiti wa kwanza wa kuamua athari za athari za dawa za kulevya. Hakuna database ya shirikisho kamili bado ipo juu ya mauaji ya wingi - ingawa Towers anasisitiza kwamba moja inahitajika sana - kwa hivyo timu yake ilichimba vyanzo vingine vya habari. Kampeni ya Brady ya Kuzuia Ukatili wa Bunduki ilikusanya data juu ya mauaji ya risasi ya shule 188 kutoka 1998 hadi 2013, na 477 ya risasi za wingi (mauaji ya risasi ya watu watatu au zaidi lakini sio lazima vifo) kutoka 2005 hadi 2013. Kwa mujibu wa ripoti ya utafiti wa Marekani, mauaji ya watu wanne au zaidi yalipatikana katika kipindi cha mwaka 2006 hadi 2013. Takwimu hizo zilitokana na ripoti zilizotolewa kwa FBI na pia na rekodi za idara za polisi za mitaa ambazo mara nyingi hazipelekwi kwa mamlaka za shirikisho. "Today ilionyesha ""kutoweza na usahihi"" katika ripoti za uhalifu kama huo, kwa hivyo Towers na timu yake waliingiza data tu ambazo wangeweza kuthibitisha." "Wakati data zilizochanganywa zilipochunguzwa kwa ujumla, ilifunua kwamba mauaji ya watu wengi na mauaji ya risasi shuleni yanaonekana kuunda kipindi cha kuambukiza ambacho huchukua karibu wiki mbili, wakati ambao uhalifu kama huo una uwezekano mkubwa wa kutokea, ""timu hiyo inaripoti wiki hii katika PLOS ONE." Utafiti wa awali unaonyesha kwamba aina nyingine za uhalifu na jeuri zaweza pia kuambukiza. Inaonekana kwamba kujiua, kwa mfano, nyakati nyingine kunaweza kuwafanya watu wengine walio hatarini wajiue. "Katika miji mikubwa, hawachapishi habari nyingi kuhusu mauaji ya kujiua ambayo yanaweza kutokea kwenye daraja, kwa mfano, kwa sababu imeonekana kwamba mauaji ya kujiua yanaweza kuambukiza, kwa hivyo hawawapi chanjo nyingi kujaribu kusaidia kukandamiza hilo. """ "Wanahabari wanaamini kwamba ""usambazaji wa habari usio na kikomo wa mauaji ya hali ya juu na watu wanaowatenda"" labda hucheza jukumu katika athari yoyote ya kuambukiza ambayo ipo." "Maelezo ya matukio haya hufikia kwa urahisi idadi ndogo ya watu waliovurugika vya kutosha kufikiria kufanya zaidi, ""waandishi wanasema." Hii inaungwa mkono na ukweli kwamba kuambukizwa haionekani kuwepo kwa uhalifu ambao haupati umakini wa kitaifa. Uchunguzi wa timu ya uchunguzi wa mauaji ya watu wengi ya watu watatu au zaidi, lakini sio lazima vifo, haukupata ushahidi wa maambukizi. "Tuliamua kwamba matukio hayo yalikuwa ya kawaida sana hivi kwamba mara chache yalichapishwa katika habari za mahali hapo", anaeleza Towers. <unk>Kwa hiyo sisi theorize kwamba ni kwa nini hatukupata ushahidi wa takwimu kwa ajili ya maambukizi katika seti hiyo ya data. Kwa sababu ni watu wachache sana ambao wanaweza kufanya kazi hii, hakuna habari za kutosha kwa idadi kubwa ya watu. Nadhani inaweza kuwa kwamba tu chanjo ya kitaifa ina uwezo wa kufikia watu wa kutosha. <unk> chanjo ya vyombo vya habari ni mbali na sababu pekee inayohusika, Towers anasisitiza. Ni wazi kwamba matatizo ya afya ya akili huchangia sana. Kulingana na utafiti huo, upatikanaji wa bunduki ni muhimu. "Kitu kingine ambacho kimetokea ni kwamba matukio ni ya juu zaidi katika majimbo ambayo yana ueneaji mkubwa wa umiliki wa silaha za moto", Towers anasema. <unk> Hiyo inaonekana kuwa kucheza jukumu. Unapopata mtu ambaye ni kihisia au kiakili distressed, basi wao pia kuwa na upatikanaji wa silaha, na ni mchanganyiko mbaya. <unk>