INTRODUCTION (citations omitted)

Incarceration rates (numbers of prisoners per capita) are a basic indicator of how government’s use of the prison sanction permeates into the population as a whole—a concept I will call carceral intensity. If we view incarceration as a subtraction from the life of a community—or a succession of blows that are “felt” by the community—then the density of coercive “hits” within a geographic area or population group is a matter of compelling social importance.

Incarceration rates are capable of conveying the human stakes of prison policies with leaden force. For example, The Pew Charitable Trusts published a much-cited finding that “1 in 100” American adults were in prison or jail at yearend 2006—or “1 in 54” adult males. Such measurements become especially vivid when we unpack the confinement rates of racial and ethnic minorities. For example, Pew’s researchers also reported that approximately “1 in 9” black men aged 20–34 were in prison or jail. This is a finding that should rivet everyone’s attention.

As a statistical tool, incarceration rates hold tremendous power and rhetorical meaning. For those interested in the past and future of mass incarceration in America, incarceration rates are starting points for debate, basic units of research, sources of insight, triggers of moral emotions, and bullet points for advocacy. Accordingly, they should be treated with care. We should be wary about statistical uses that are nonsensical or misleading. Unfortunately, this is already a problem in the young field of incarceration scale (IS). As shown in this paper, it is surprisingly problematic to measure and describe trends in carceral intensity over time.

Change in incarceration rates—on a magnificent scale—has been a defining feature of American criminal justice over the last several decades. From 1972 to a peak in 2007-08, the nation’s prison-and-jail confinement rate quintupled, putting the U.S. firmly in the “world-leadership” position. Astonishingly, all states and the federal system participated in this upward drive, albeit to varying degrees. Since 2008, there have been modest declines in carceral intensity across the country as a whole (half of the drop comes from California alone). Today, many people at the national, state, and local levels hope to see significant reductions in America’s prison and jail populations. The subject of American incarceration policy, past and future, forces us to think in terms of large increments of change.

This article is about how we quantify and perceive changes in incarceration rates, what we mean when we say that some states have had more incarceration growth than others, and what metrics we should treat as “success” when states experiment with prison-population controls. Because American states have broadly diverse systems of criminal punishment, it is important to ask which states and system-types had “more” versus “less” uncontrolled growth during the nation’s prison buildup decades. Now that the peak of the buildup appears to have passed, it will be just as urgent to study the records of jurisdictions that adopt reforms intended to reduce their prison rates, isolate instances of success, and explore why some states continue to increase their use of confinement. Indeed, it is hard to imagine not asking comparative questions about incarceration-rate change when charting course toward the possibility of a post-mass-incarceration era.

This paper examines a foundational question of measurement in the IS field: When comparing the U.S. with other countries, or when analyzing the different etiologies of mass incarceration across American states, should changes in imprisonment rates be stated as the percentage of change in rates from Time 1 to Time 2, or as the absolute change in rates? This can be abbreviated as a choice between the percentage-change method (PCM) and the absolute-change method (ACM). To illustrate the alternatives using Bureau of Justice Statistics data, we can say that the prison rate in Mississippi rose by 786 percent from 1972-2008—a percentage-change measure. Alternatively, we can say that Mississippi’s prison rate rose by 652 per 100,000 general population over that time period—an absolute-change approach. Either statement is based on a reported increase in Mississippi’s prison rate from 83 per 100,000 general population in 1972 to 735 per 100,000 in 2008.

Both calculations are mathematically impeccable, but which of the two measures gives us the most useful information from a policy perspective? This simple methodological riddle has large implications for how we perceive comparative prison growth across jurisdictions, and the policy conclusions we draw from those observations.

What gives this article significance, and justifies its extended analysis, is that the PCM is overwhelmingly the favored measure within the IS field, government agencies, the criminal justice profession generally, and the media. It is very difficult to persuade people they should rethink its use. And yet, for the purposes of measuring prison-rate change, especially when the task at hand involves comparisons across jurisdictions, long time periods, or different time periods, the PCM is deeply flawed. It tells us a story that is true but largely irrelevant to the values important to human beings, communities, and societies when thinking about incarceration growth. It tells us nothing about variations in carceral intensity or, worse, points us in the wrong direction. This article will argue that the ACM—or some other alternatives one might suggest—would give us clearer vision into the past and future of American incarceration policy.

Read the full article.

This article was originally published in the Berkeley Journal of Criminal Law.