Admission to a federal or state prison is a possible outcome of a complex, adaptive and adversarial process that is most frequently initiated by an arrest by a city or county law enforcement agency. The usual practice in the study of a complex process is to break it down into a set of simpler components. An adaptive system is time dependent and historical data can be used to study how the process responds to environmental changes.
I classify myself as an outside observer of corrections who became interested in the subject in 2000 when our county jail had three inmates in a cell designed to hold one. I was able to help the Sheriff reduce the number from three to two a small improvement. Since then progress has been made in a series of small steps at a slow pace. It is very hard to tell if I made any difference.
What I am doing now is collecting and studying historical prison data. Most of the posts in this website are about state prisons because much of the writing about prison policy is about the federal system because it has a larger audience. I thought it would be useful to have a source on the web that provides the results of analysis of state prison data.