STUDIES:
832/
“The significant [police data] effects appear to be intentional violation of Massachusetts state law mandating the reporting of race and ethnicity.” & “Race and ethnicity missingness is significantly more likely in agencies with higher proportions of Black … residents."

Race and Ethnicity Missingness in the Traffic Stop Data Reported by 308 Massachusetts Police Agencies
Race and Justice
Vol. 2 Issue 1, pp. 42–65,
2012
Comment on this study on its Twitter thread.