Why are there so many people in prison in America?

Sun, May 7, 2017 - Daniel Von Fange

It’s true that American has more total inmates than any nation on earth.

Obviously for a fair comparison we’d also need to consider population size. Even by this metric, America is #2 in the world.

First here is the Seychelles, off the coast of Africa in the Indian Ocean. The Seychelles had a 4.5x increase in prison population in the last ten years. The Russia Federation used to have the world’s largest prison population rate in 2000, but has seen almost a 50% decrease since then. (I’d love to know what made these huge , rapid changes in these nations)

A lot of people locked up in America. But what are they in for?

Any discussion on this these days quickly brings up the statistic “fifty percent of prisoners are in prison for drug charges”. But that’s missing an important word. The actual statistic is that fifty percent of Federal prisoners have their most serious charge drug related.

However Federal inmates make up only about 10% of inmates in the America. State prisons hold most of the inmate population. Since federal laws are different than state laws, there’s likely to be a difference in inmate charges.

To get an actual idea on why America’s prisons are so full, I needed to look at state prisons. South Carolina has a lot of statistics easily available.

I pulled up a breakdown of total inmate population, by most serious offense. Only 16% were there on drug related charges.

The most common inmate offense wasn’t drugs - it was murder(18.7%)! And more than one in four people in state prison in South Carolina were there for either homicide or rape. More than 54% were in prison for some form of violent crime classification - Homicide, Robbery, Assault, Sexual Assault/Rape, and Kidnapping. That’s not even counting armed home invasions, which fall under Burglary.

How could this be! South Carolina doesn’t seem that dangerous.

Then I figured it out. Per offense, inmate population is not only proportional to the number of crimes of that type that happen, but is also multiplied by the length of the sentence for that crime. So if someone is in prison for a murder sentence of thirty years, then for thirty years they count towards the number of homicide inmates, while a first time, unarmed burglar could only be counted for one year towards the “burglary” statistic. For there to be a matching inmate ratio between 30-year terms and 1-year terms, there would need to be thirty times more 1 year convictions.

Prison populations skew far more violent than even the criminal population because of this.

In the big picture, there’s been a huge reduction in the amount of crime in the US in the last twenty years. We’d expect to see the prison population declining, and it is.

But there’s a strange effect from this reduction in crime.

Imagine if instantly, one day, no new prisoners were sent to prison in South Carolina ever again. Would the prisons be empty that day? No. It would take a while for the existing inmates to reach the end of their sentences.The the shorter sentences would clear out first. After five years, there would only be people left who have sentences longer than five years. After fifteen years, most remaining inmates would be there on extremely violent crimes with long sentences. The ratios would have shifted even more to violence, and in a big way.

Now if instead of cutting crime to zero, we cut crime in half. That’s what actually happened. Then we would see a half sized version of the same effect.

As an approximation, all of the murders from fifteen years ago, back when murder rates were much higher, are still in prison today. However, all the sentences for non-violent burglaries from fifteen years ago, when burglary rates were also much higher, have all been over for a long time and no longer are in the prison population at all.

So a counter-intuitive result of a reduction in all kinds of crime, is that a proportionally greater percentage of inmates in prison on violent charges, at least for a few decades after the change.

Jumping back to the opening question, it seems like the single biggest contributor to America’s huge prison population is people serving long sentences for violent crimes.

But why does American have so many people serving long sentences for violent crimes?

Well, roughly speaking, the prison population for a given crime is:

Occurrence Per Year x Report Rate x Solve Rate x Conviction Rate x Prison Sentence Length.

In all of those, American ranks either high or very high. We do have some cultures in America with extremely high violence rates, and others with just double European rates rates. People in America tend to report violent crimes to the police, the police tend to solve them most of the time, and prosecutors successfully prosecute them at an ever increasing rate. Also, as a response to the crime wave of the 1970’s and 1980’s, states in increased the sentence length for many crimes. For example, murder has a minimum sentence in South Carolina of thirty years compared with a minimum sentence in Sweden of ten years.

So what should we expect for the next ten years? As long as crime rates remain about the same, I’ll expect the current gradual decline to continue for the next decade, with a little more decline added by what seems to be a reduction in prosecution for some drug related crimes.

Working against this in the long term, is that police still have quite a of bit room to get better at catching criminals. Murders are the crime with the highest rate of “clearing”, and yet are only cleared 66% percent of the time.

Secondly, the rate of homicides in the US has been going up quite a bit for the past two years. This is supposedly a localized effect of a few high crime cities, but even in South Carolina the number of people in prison for murder has gone up by about 10% in just the last four years. This is concerning.