Does widespread media coverage of mass shootings increase the likelihood of future mass shootings? It seems intuitive that the answer could be 'yes'. Perhaps media coverage encourages 'copycat' behaviour. Perhaps, the prospect of fame motivates mass shooters, and regular media coverage provides the avenue to fame (or, rather, infamy). Maybe media coverage simply makes mass shootings seem 'more normal', as a response to some slight. Teasing out which of these explanations is correct is difficult, especially when you consider that the direction of causality isn't even established. Does media coverage lead to more mass shootings (as the theories outlined above suggest), or do more mass shootings simply lead to more media coverage?
Those are the questions that this recent article by Michael Jetter (University of Western Australia) and Jay Walker (Old Dominion University), published in the journal European Economic Review (sorry, I don't see an ungated version online), set out to address. Jetter and Walker obtain data on mass shootings (four or more victims) for the period from 2006 to 2017, from USA Today's Behind the Bloodshed database. To understand the extent of the problem, they highlight that:
...265 (or six percent) of the 4383 sample days from 2006 to 2017 experienced at least one mass shooting, whereas nine days saw two mass shootings.
Jetter and Walker then collect data on television news from the Vanderbilt Television News Archive. They count the number of news segments from ABC World News Tonight (the highest-ranked evening news programme in the US) that contain the terms 'shoot' (including 'shooter' and 'shooting'). They then filter out false positives manually (such as news items about the shooting of a movie). They find 490 news segments on shootings over the 2006 to 2017 period.
Their analysis relies on an instrumental variables (IV) approach, to avoid the reverse causality problem and obtain the causal effect of news on shootings. To achieve this, they need to identify an instrument that affects the amount of news on shootings, but doesn't directly affect the number of shootings. They suggest disasters in other countries, where large numbers of US expatriates live. Jetter and Walker collect data on disasters from the International Disaster Database, limiting the data to countries with at least 50,000 US emigrants. They note that:
In total, we capture 158 such disasters (132 earthquakes, 10 epidemics, and 16 events of volcanic activity) that span 950 days out of our 4383 sample days.
It turns out that disasters are a good predictor of shooting news (because more disaster news leaves less room in the news broadcast for shooting news). In their IV analysis, Jetter and Walker find that shooting news is:
...a positive, statistically significant, and quantitatively powerful predictor of mass shootings. The corresponding magnitude indicates a one standard deviation increase in shooting news (0.389) translates to an increase in the number of shootings by approximately 73% of a standard deviation.
Now, looking over the time after shooting news, they find that:
The derived coefficients decrease in magnitude and eventually turn statistically indistinguishable from zero after 3-4 weeks.
So, news coverage of shootings causes an increase in mass shootings, and the effect lasts for up to 3-4 weeks. The next question is, why? Jetter and Walker look further into the data, and find no causal relationship from news coverage to murder more generally. That rules out salience, or that shootings are seen as 'more normal' after news coverage of shootings. They find that the mass shootings are more likely to happen on or after the anniversary of other infamous mass shootings, which suggests a behavioural contagion (or 'copycat') effect. Finally, they find that mass shootings are no less likely to happen on days where there would be predictably less change of news coverage (such as the dates of the Super Bowl, Olympics, Academy Awards). That would seem to rule out fame as a significant motivator, since a mass shooter who wants to be famous would probably want to avoid those dates, and yet they don't. So, Jetter and Walker conclude that:
Taken together, the results... are consistent with a behavioral contagion model...
Mass shooters are copycats. And then, in terms of policy implications:
First, our results advise journalists to report less on mass shootings... Second, our results also explain (at least in part) why shootings sometimes cluster in short intervals... Thus, police and other security forces may be well advised to be alert on and after days of heightened media coverage of mass shootings.
In the Waikato Economics Discussion Group a couple of weeks ago, we discussed this paper. We decided you couldn't really replicate this analysis for New Zealand, as (thankfully) mass shootings are very rare. However, one student made mention of ram raids, which have attracted massive attention in the media, this year in particular (for example, see here). Is media coverage of ram raids driving up the number of ram raids in New Zealand? The arguments are very similar to those in the Jetter and Walker article. Whether ram raids are driven by media coverage is an interesting question, and one that may be well worth following up on in an Honours or Masters research project.
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