US prisons have grown dramatically over the past 50 years.

In the early 1970s, the prison population began to rise. The causes are still widely debated, but there is a bi-partisan effort to reduce it, colloquially known as solving “mass incarceration”.

For example, there are currently 473 people in prison for every 100,000 citizens, 4x higher than in 1975. In Louisiana, it’s 868 prisoners per 100,000: over 0.8% of the population.

Was it the war on drugs?

Drug offenders make up 15% of prisoners. Murderers? 13%. Drug offenses peaked in the year 2000 at 24%. While drug offenders are a large part of public discourse, any meaningful prison population reduction must address the remaining 85% of offenders, more than half of whom have been convicted of a violent crime. Prison Population, by Offense

Most people admitted to prison will be out in 1 year.

Lengthy time-served in prison (over 5 years) is not the norm. Of all inmates admitted in the year 2000, 62% were out in 2 years. Over the course of 5 years (in 2005), 86% had been released. Drug offenders serve even less time – 95% are out in 5 years. Those serving 10+ years or life-long sentences make up a small fraction of each year’s admissions. State Prison Admissions from 2000 Time served by inmates admitted to state prison

Even with low time-served (half admitted are out in 1 year), we refill prisons with about the same number of people each year.

On Jan 1 2015, there were 1.5M people in prison. We then released 640K people over the next 12 months, an astounding amount! So why was the prison population back up to 1.5M at year-end – the same amount as the start of the year? We admitted 608K people in 2015, nearly the same number who were released. The Turnover Rate of Prisons Year-end Prison Population, Admissions, and Releases, 2010 - 2015

This is why measuring the prison system is so difficult: time served matters a lot. On Jan 1 2013, there were 282K drug offenders in prison. On Dec 31 2013, there were 209K. A reduction of 79K!

But one-day counts are only part of the puzzle. We miss what happened in those 12 months: we admitted 189K drug offenders and consequently released 262K. This is an enormous turnover rate – we admitted almost as many people as were left at the end of the year!

Similarly, violent offenders were 27% of 2015 admissions. but when you take into account sentence length, they represent a much larger impact on the prison system.

Admitted People vs. Admitted Time Served State Prison Admissions from 2000

US Prisoners on Dec 31, ‘15 : Filter by Offense = 150 prisoners 2015 Prisoner Population 14% Drug Offenders 23,000 people Sentence Lengths All Offenders 1 yr 25% 1 yr 25% 1 yr 25% filter

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year Autoplay 1970s 1980s 1990s 2000s 2010s 2010 2011 2012 2013 2014 2015

Private prisons hold 8% of inmates, up from 5% in 1999.

The debate surrounding private prisons has garnered national attention, yet the overall amount has increased slightly in the past 18 years.