Crime and its prevention has become a much debated issue. Claims and counter claims are made as to the real extent and the possibility of controlling crime. Law makers are considering legislating heavier sentences, which raises questions about the role of prison sentences in crime prevention. Most discussions of crime and its prevention lack a way of generating quantitative estimates of what alternative policies would achieve and what they would cost. A recent paper by one of the authors (Avi-Itzhak and Shinnar, 1973) attempts to develop a mathematical model simple enough to make approximate quantitative estimates based on available statistical information. In this paper we try to simplify the model further and to present it in a way that will make it more accessible to the policy maker and social scientist. We also try to apply it to conditions in New York.