You don’t actually need a control to make claims about what fraction of police officers are “decent people”. Even if, hypothetically, decency were determined c

You don’t actually need a control to make claims about what fraction of police officers are “decent people”. Even if, hypothetically, decency were determined completely by external factors that happen to correlate with being a police officer, that wouldn’t change the fact that any police officer you meet is likely to be less (or more) decent than some baseline of people in general. Though, of course, the source itself may be making stronger claims…