Jerry Ratcliffe and Evan Sorg were involved in two in-depth experimental evaluations of foot patrol with the Philadelphia Police Department. In their book, they discuss two different studies: The Philadelphia Foot Patrol Experiment and the Policing Tactics Experiment. I would like you to summarize each study (each study's explanation should be at least four paragraphs). 

Explain how the results differed, and discuss at least two of the reasons why the results may differ according to the authors