Why Are So Many Americans in Prison?

Chapter 2. Understanding and Documenting the Determinants of Incarceration Growth

chAPter 2 understanding and documenting the determinants of Incarceration Growth There are several stylized facts about the U.S. prison population that the lay reader is likely to find surprising. First, prisons are often mischaracterized as places where we lock people up and throw away the key. In fact, the typical person admitted to prison on a new felony conviction is likely to be released after two years, with many offenders serving less time and some serving considerably more time. These relatively short terms have prompted the observation (and frankly, the admonition) by Jeremy Travis (2005), the president of the John Jay College of Criminal Justice, that “they all come back.” Second, few outside of those who work within the criminal justice system are aware of the degree of fluidity in the prison population—in particular the extent to which the prison population turns over from year to year. For example , on December 31, 2007, there were 1,598,316 inmates in state or federal prison. During the calendar year 2007, 751,593 inmates were admitted to prison (47 percent of the year-end population), while 725,402 were released from prison (roughly 45 percent of the year-end total). In some states, the degree of turnover is unusually high. For example, California, which, with 174,282 inmates at the end of 2007 held over 10 percent of the nation’s prison inmates, released 135,920 inmates and admitted 139,608 that year. To understand the factors driving growth in the U.S. incarceration rate, we UNDERSTANDING AND DOCUMENTING THE DETERMINANTS 33 need a framework for characterizing what determines the size at a given point in time of what is inherently a dynamic population. In our research on U.S. prisons, we have found the analogy of the student body at a university to be particularly useful. Suppose that we wish to start a four-year undergraduate institution from scratch. We build the buildings, hire the necessary professors and staff, and admit our first freshman class of 1,000 students. In our first year of operation, we thus have a relatively small student population of 1,000. In year two, our 1,000 freshmen become sophomores (assuming everyone progresses on schedule), and we admit a new class of 1,000 freshmen, increasing the student body to 2,000. Similar progression and new admissions in years three and four increases our student body to 3,000 and 4,000, respectively . In year five, however, the effect on our total student body of 1,000 freshman admissions is perfectly offset by the graduation of our original cohort of 1,000 students. Hence, beyond year four our student body stabilizes at a population of 4,000 with the number exiting (our graduates) exactly offset by the number entering (the new freshmen). The eventual stability of our student body provides an example of a dynamic population reaching what is often referred to as the “steady state.” When such a population is in a steady state, exits equal admissions and the population is constant from period to period. Of course, the members of the population change from year to year as the new freshmen replace the graduating seniors. However, our student body attains a predictable and stable total. The usefulness of this analogy is in highlighting factors that would lead to long-run changes in the size of the student body. For example, suppose we decide to permanently increase freshman admissions to 1,100. In the first year following this change, this decision leads to an increase in the student body to 4,100 as freshman admissions more than offset graduating seniors. However, it takes four years for the full impact of this policy change to be realized. Eventually, there are 1,100 students in each year and the size of our student body shifts to a new steady state of 4,400. The change in the steadystate population caused by increased admissions exactly equals the number of new admissions multiplied by the number of years each new admission will study at the university. Alternatively, suppose we are prompted to add one more year of study to the undergraduate program because the students do not seem to be learning enough in four years. With 1,100 admissions per year and five required years 34 WHY ARE SO MANY AMERICANS IN PRISON? of study, our student population will eventually stabilize at 5,500. We...