Study Finds More Private Prisons Result in Judges Imposing Slightly Longer Sentences
by Matt Clarke
In a report published on March 24, 2019, researchers from Columbia University and UCLA found that “the opening of a private prison increases the length of sentences relative to what the crime’s and defendant’s characteristics predict.” Private prisons did not increase the chances of defendants being incarcerated, as opposed to receiving probation or some other form of alternative sentence, but did increase the prison terms of defendants who would have been sent to prison anyway.
The core finding was that a doubling of private prison capacity led to an increase in average sentence length of 23 days, or 1.3 percent. The findings were statistically significant.
The report – titled “Do Private Prisons Affect Criminal Sentencing?” – involved 13 states that straddle 16 state borders, and focused on trial courts in adjacent across-border counties. This allowed the study to control for local trends in crime and other local effects while comparing different private prison circumstances. It focused on their effect on the sentencing practices of state judges.
A comparison of sentencing during election years and non-election years showed no private prison influence on sentence length. Sentences increased as elections approached, but that was attributed to the electorate calling for harsher sentencing. Harsher sentences as elections drew near did not increase when private prisons were present, making it unlikely that private prison firms were influencing judges via campaign contributions, which likely would have exacerbated the effect of approaching elections on judges’ sentencing decisions.
The study concluded that the most likely private prison-related influence on judges’ sentencing practices was the savings they offered, or were perceived to offer, compared to state-run prisons. The report noted that previous studies had found no clear evidence that private prisons result in lower average costs of incarceration, but there was some evidence they result in lower marginal costs. The reason was that some states with private prisons require them to have a lower per-diem cost than the average cost of incarceration in the state prison system. This gives the appearance of savings for private prisons compared with public prisons.
For example, Kentucky, Mississippi and Texas require private prisons to have per diem costs that are 10 percent lower than the average cost for state-run prisons.
However, the states do not actually save 10 percent because private prisons limit which prisoners they house, often excluding prisoners with higher security classifications and serious medical conditions who are expensive to treat. In other words, the private prisons do not house an average cross-section of state prisoners, but rather cherry pick the least expensive prisoners to incarcerate. Since the prisoners who are less expensive to incarcerate are removed from the state prison system, the average cost of incarceration in state prisons increases and little if any savings are realized.
However, judges are likely to believe that private prisons reduce incarceration costs and allow those perceived savings to influence them to sentence defendants to longer prison terms. The study found the effect was twice as large for states with high savings requirements for private prisons.
The study also found weak evidence of election cycles causing increased sentences and compelling evidence of racial biases in sentencing, but no evidence that private prisons increased either of those influences. It concluded that the increased use of private prisons results in a moderate increase in sentence lengths, primarily due to judges perceiving – incorrectly – that private prisons offer lower incarceration costs.