It points out that they look at data for 99% of US counties, which rules out a simplistic attribution of crime to population density, and describes some of the data cleansing. They also claim it corroborated findings elsewhere.
Since this is a data review presumably other centres can repeat the analysis to confirm the correlation result at least, and medical researchers could conceivably find a real experiment to establish causality.
https://pierce.atmos.colostate.edu/Monthly_Pollution_and_Cri...
It points out that they look at data for 99% of US counties, which rules out a simplistic attribution of crime to population density, and describes some of the data cleansing. They also claim it corroborated findings elsewhere.
Since this is a data review presumably other centres can repeat the analysis to confirm the correlation result at least, and medical researchers could conceivably find a real experiment to establish causality.