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Importantly, this study design permits
adjustment for potential confounding factors that could be related to both album release timing
and traffic fatality risk (e.g., albums tend to be released on Fridays) while still taking advantage
of the otherwise exogenous variation in album release timing.
They seem to control for day of week:
Edit: Direct link to full paper: https://www.nber.org/system/files/working_papers/w34866/w34866.pdf