Comments on Schildkraut and Turanovic 2022 "A New Wave of Mass Shootings? Exploring the Potential Impact of COVID-19"
Homicide Studies recently published Schildkraut and Turanovic 2022 "A New Wave of Mass Shootings? Exploring the Potential Impact of COVID-19". From the abstract:
Results show that total, private, and public mass shootings increased following the declaration of COVID-19 as a national emergency in March of 2020.
I was curious how Schildkraut and Turanovic 2022 addressed the possible confound of the 25 May 2020 killing of George Floyd.
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Below is my plot of data used in Schildkraut and Turanovic 2022, for total mass shootings:
My read of the plot is that, until after the killing of George Floyd, there is insufficient evidence that mass shootings were higher in 2020 than in 2019.
Table 1 of Schildkraut and Turanovic 2022 reports an interrupted time series analysis that does not address the killing of George Floyd, with a key estimate of 0.409 and a standard error of 0.072. Schildkraut and Turanovic 2022 reports a separate analysis about George Floyd...
However, since George Floyd's murder occurred after the onset of the COVID-19 declaration, we conducted ITSA using only the post-COVID time period (n = 53 weeks) and used the week of May 25, 2020 as the point of interruption in each time series. These results indicated that George Floyd's murder had no impact on changes in overall mass shootings (b = 0.354, 95% CI [−0.074, 0.781], p = .105) or private mass shootings (b = 0.125, 95% CI [−0.419, 0.669], p = .652), but that Floyd's murder was linked to increases in public mass shootings (b = 0.772, 95% CI [0.062, 1.483], p = .033).
...but Schildkraut and Turanovic 2022 does not report any attempt to assess whether there is sufficient evidence to attribute the increase in mass shootings to covid once the 0.354 estimate for Floyd is addressed. The lack of statistical significance for the 0.354 Floyd estimate can't be used to conclude "no impact", especially given that the analysis for the covid declaration had data for 52 weeks pre-declaration and 53 weeks post-declaration, but the analysis for Floyd had data for only 11 weeks pre-Floyd and 42 weeks post-Floyd.
Schildkraut and Turanovic 2022 also disaggregated mass shootings into public mass shootings and private mass shootings. Corresponding plots by me are below. It doesn't look like the red line for the covid declaration is the break point for the increase in 2020 relative to 2019.
Astral Codex Ten discussed methods used to try to disentangle the effect of covid from the effect of Floyd, such as using for reference prior protests and other countries.
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NOTES
1. In the Schildkraut and Turanovic 2022 data, some dates appeared in different weeks, such as 2019 Week 11 running from March 11 to March 17, but 2020 Week 11 running from March 9 to March 15.
2. The 13 March 2020 covid declaration occurred in the middle of Week 11, but the Floyd killing occurred at the start of Week 22, which ran from 25 May 2020 to May 31 2020.