Comments on Peay and McNair II 2022 "…The dual influences of #BlackLivesMatter on state-level policing reform adoption"
I'll hopefully at some point write a summary that refers to a lot of my "comments" posts. But I have at least a few more to release before then, so here goes...
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Politics, Groups, and Identities recently published Peay and McNair II 2022 "Concurrent pressures of mass protests: The dual influences of #BlackLivesMatter on state-level policing reform adoption". Peay and McNair II 2022 reported regressions that predicted a count of the number of police reform policies enacted by a state from August 2014 through 2020, using a key predictor of the number of Black Lives Matter protests in a state in the year after the killing of Michael Brown in August 2014.
An obvious concern is that the number of protests in a state is capturing the population size of the state. That's a concern because it's plausible that higher population states have legislatures that are more active than smaller population states, so that we would expect these high population states to tend to enact more policies per se, and not merely to enact more police reform policies. But the Peay and McNair II 2022 analysis does not control for the population size of the state.
I checked the correlation between [1] the number of Black Lives Matter protests in a state in the year after the killing of Michael Brown in August 2014 (data from Trump et al. 2018) and [2] the first list of the number of bills enacted by a state that I happened upon, which was the number of bills a state enacted from 2006 to 2009 relating to childhood obesity. The R-squared was 0.22 for a bivariate OLS regression using the state-level count of BLM protests to predict the state-level count of childhood obesity bills enacted. In comparison, Peay and McNair II 2022 Table 2 indicated that the R-squared was 0.19 in a bivariate OLS regression that used the state-level count of BLM protests to predict the state-level count of police reform policies enacted. So the concern about population size seems at least plausible.
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This is a separate concern, but Figure 6 of Peay and McNair II 2022 reports predicted probabilities, with an x-axis of the number of protests. My analysis indicated that the number of protests ranged from 0 to 87, with only three states having more than 40 protests: New York at 67, Missouri at 74, and California at 87. Yet the widest the 95% confidence interval gets in Figure 6 is about 1 percentage point, at 87, which is a pretty precise estimate given data for only 50 states and only one state past 74.
Maybe the tight 95% confidence interval is a function of the network analysis for Figure 6, if the analysis, say, treats each potential connection between California and the other 49 states as 49 independent observations. Table 2 of Peay and McNair II 2022 doesn't have a sample size for this analysis, but reports 50 as the number of observations for the other analyses in that table.
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