5 ms·

Do you know if they controlled for daytime population? As in weekdays vs weekends?

• nkassis 7y ago
  Seasons
• dTal 7y ago
  That was my immediate thought. More people = more pollution, and also more crime. The authors are aware of this and attempt to control, mainly by assuming that all confounding effects are either constant or cyclical: "We include county-by-year-by-month-by-day of the week fixed effects to control for county level unobservables that are either constant over time, such as state and county-level policies, or that are time-variant, such as changes in population density, demographic composition, seasonal variation in pollution or crime, or changes in state and county-level policies that limit pollution or crime enforcement. These fixed effects also control for cyclical within-week, within-county variation in pollution and crime. Thus, our data allows us to compare for example, the effect of changes in pollution within a series of Mondays within a given county within a given month. We argue that changes in pollution across a series of Mondays within a county-month, conditional on weather controls, is random and thus exogenous to crime." I'm not at all convinced this holds true, however - lots of systems with humans in it are chaotic rather than cyclical. I imagine if you did a plot of population over time, it would be very noisy. All it takes is a bit of aperiodic noise in the population, and tight correlations between population/crime and population/pollution, and their effect is rendered void.
• PeterStuer 7y ago
  Yes, they did.