They are saying that in evaluating police effectiveness it's important to not only consider the empirical data of case clearance rates but also to imagine how m

They are saying that in evaluating police effectiveness it's important to not only consider the empirical data of case clearance rates but also to imagine how many people might have committed crimes but were deterred. Until experiments are made to measure the effectiveness of different strategies for affecting crime rates, each person will imagine a different answer to this question based on their beliefs about human nature and society.