When we hear a number like there are 2.3 million Americans in prison or jail, that's a point in time estimate. The Bureau of Justice Statistics does a census of facilities and it varies depending on the facility. And so those numbers are essentially headcounts who's in on a given day. We can also think about, and that's the stock of inmates.
Becky Pettit of the University of Washington and author of Invisible Men talks with EconTalk host Russ Roberts about the growth of the prison population in the United States in recent decades. Pettit describes the magnitude of the increase particularly among demographic groups. She then discusses the implications of this increase for interpreting social statistics. Because the prison population isn't included in the main government surveys used by social scientists, data drawn from those surveys can be misleading as to what is actually happening among demographic groups, particularly the African-American population.