Expert Commentary

U.S. prison boom: Impact on age of state prisoners

2016 study published in Criminology that explores changes in the age distribution of prisoners during the U.S. prison boom that began in the late 20th century.


The United States has the second-highest prison population rate in the world. Of every 100,000 people in the U.S., 698 are held in penal institutions – a rate that falls behind only the small African country of Seychelles, where 799 of every 100,000 people are imprisoned, according to a February 2016 report from the International Centre for Prison Studies in London. Worldwide, an estimated 10.35 million to more than 11 million people are imprisoned. The U.S. has the largest prison population with 2.2 million people in prison or jail.

This segment of the U.S. population has experienced explosive growth during the past several decades. A 2014 report from the National Research Council shows that, since the mid-1970s, the rate of incarceration has more than quadrupled. In 1972, 161 of every 100,000 U.S. residents were incarcerated. The growth of the nation’s penal system and higher rates of incarceration are primarily the result of harsher sentencing policies, which increased the likelihood of imprisonment as well as the length of prison sentences.

As prison populations swelled, the size and number of prisons were not the only factors that changed. The growing imprisonment rate also has changed the demographics of the nation’s prisons. A 2016 study published in Criminology, “How the U.S. Prison Boom Has Changed the Age Distribution of the Prison Population,” explores the nature of those demographic changes as well as the reasons behind them. The authors — Lauren C. Porter of the University of Maryland; Shawn D. Bushway and Hui-Shien Tsao of the University at Albany, SUNY; and Herbert L. Smith of the University of Pennsylvania – looked specifically at the demographics of state prisons, which hold the majority of U.S. prisoners. They analyzed data collected by six waves of the Survey of Inmates in State Correctional Facilities between 1974 and 2004.

Their key findings include:

  • Prisoners have gotten older since the beginning of the prison boom. In 1974, 16 percent of prisoners were 40 years old or older. In 2004, the proportion had more than doubled to 33 percent.
  • The average age of prisoners dropped between 1974 and 1979 but then steadily rose from then until 2004. In 1974, the average age was 29.7 compared to 35.2 in 2004.
  • The shift in prisoner age is largely due to changes related to the age of individuals when they enter prison. This finding “contradicts popular wisdom for the growth and aging of the correctional population, which often points to a period effect driven by harsher sentence lengths during the 1980s and 1990s.”

The authors note that it is difficult to overstate the significance of these demographic shifts. Because a large portion of men have their first child sometime between the ages of 25 and 34, the age-distribution trend would indicate that more children are growing up while their fathers are behind bars. The authors also suggest that policies focusing on reducing sentence lengths may not address the aging issue. They point to a 2013 study from the U.S. Bureau of Justice Statistics that shows that the average age of people convicted of felonies in the U.S. rose by 4 years between 1990 and 2009. The current study’s findings “should lead both researchers and policy makers to reconsider the consensus that changes in the prison population are a result of increased sentence lengths,” the authors state.

Related research: A 2015 study from a scholar at Cornell University considers the impact of paternal incarceration on children’s social and behavioral development. A 2015 collection of research examines prisoners’ relationships with detention center staff. A 2014 study published in Criminal Justice Policy Review explores whether reductions in mental hospital populations have influenced imprisonment rates.


Keywords: incarceration, imprisonment, prison growth, jail, demographics, prison boom, prison population

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