Has anyone ever done research to see if pervasive use of facial recognition has any real effect on reducing crime?
Be careful with this line of thinking.
"cleared" generally means either an arrest was made (not a conviction) or they would've made an arrest but weren't able to (i.e. suspect died). A drop of a clearance rate just means it dropped. It only means cops in the past arrested people more often not that they actually arrested (or convicted) the correct people.
[1] https://www.theguardian.com/tv-and-radio/2017/sep/29/larry-d...