We have plenty of police officers in America

Jennifer Doleac says we need more cops on the street. One reason is that we're not good enough at catching criminals:

Right now, the probability of getting caught across the United States is low and falling. Clearance rates — in simplified terms, the number of arrests per reported offenses — were just 41 percent for violent crimes (including homicide) in 2023.

This is true, but I doubt it has anything to do with the number of police officers, which has been steadily rising even as crime rates have fallen by more than half:

My suspicion is different. Here are clearance rates for violent crime:

The clearance rate starts out fairly stable at around 50%, then drops and recovers between 2000-13. The first decline after that is in 2014, and the clearance rate dropped sharply in the decade after that. This means it could be related to Ferguson (2014), but probably not since the decline lasted so long. And it predates both George Floyd (2020) and the pandemic (2020-21), so they aren't likely at fault either.

So what could it be that started around 2014 and kept going for a decade? My guess is NIBRS, the FBI's new and improved crime reporting system. The number of police departments using NIBRS first reached a critical level around 2012 and continued to increase through 2022, when usage reached 80% and started to flatten out. My guess is that NIBRS tightened the criteria for "cleared" in some way, and as more police departments made the switch their official clearance rates went down even though they weren't doing anything different.

In other words, it's all a statistical artifact, one of many that NIBRS introduced. I don't think that FBI crime data is entirely worthless these days, but you have to be very careful with it. The decade-long switch to NIBRS has really bollixed things up.