Does crime explain the exceptional US incarceration rate?

by braces2 min read15th Aug 202027 comments

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World Optimization
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Open Philanthropy motivates their criminal justice grants with sentences like this: "The United States incarcerates its residents at a higher rate than any other major country. "

This sounds bad, but conservatives argue that this is because of our uniquely high crime rate. I didn't see any straightforward research looking at incarceration and crime rates across countries, so I did some simple analysis below.

One-line summary: the US's incarceration rate is still surprisingly high accounting for its homicide rate.

Update on 8/16/2020: Crossposting from here:

We don’t have an incarceration problem—we have a crime problem…The critics of ‘mass incarceration’ love to compare American incarceration rates unfavorably with European ones. Crime is inevitably left out of the analysis.

That’s from Heather MacDonald.

It’s true that the US incarceration rate is rarely presented next to crime rates. For instance, a famous statistic is that the US has around 20 percent of the world’s prisoners, but we typically don’t hear people follow that with our crime victimization numbers.

So to what extent is this all a crime problem? A simple way to test this idea is to see, at the country level, how our incarceration rate scales with our crime rate compared to other countries.

I couldn’t find these plots from some basic googling so I tried doing it myself. The incarceration data is from Wikipedia and the homicide data is from the World Bank, in both cases using the most recent data available. I believe data tends to be better for homicide rates; this is meant to be a proxy for crime broadly.

Here’s the incarceration rate against the homicide rate for all countries that were in both datasets:

Incarceration rate vs. homicide rate for all countries from both datasets.

 

The green line shows the fitted values from regressing the incarceration rate on the homicide rate. The regression suggests that the incarceration rate increases by 7.1 (standard error = 1.9) when the homicide rate increases by 1, and the R-squared is 0.10.

So incarceration definitely increases with crime, but based on the R-squared and a visual assessment of the points, this isn’t a very tight fit.

And yes, the US in an enormous outlier. Below I restrict to places with 3-7 homicides for every 100k people so that it’s easier to see the countries that are similar to the US.

Incarceration rate vs. homicide rate for countries similar to the US in homicide rate.

 

What about compared to the US’s “peer” countries? I went through and haphazardly coded a list of richer nations and restricted to those. The US is quite an outlier in both ways. Our homicide and incarceration rates are around 5 times higher than that clump at the bottom. The trend line seems basically meaningless here, but we’re way above it.

Incarceration rate vs. homicide rate for “first world” countries

 

So: MacDonald’s argument supposes that the appropriate level of incarceration depends on the level of crime. But that first cross-country picture suggests that we can’t justify the US’s current incarceration rates based on how they generally scale with homicide rates in other countries.

Does this mean that our incarceration problem is not a crime problem? One response is that we should just ignore the trendline altogether because the relationship I found was too weak to be useful—other factors are more important. But then it seems it’s on the incarceration defenders to point to the crime measures that do matter and make the US seem normal.

Related to this is that so far we’ve basically taken the homicide rate as exogenous, but of course there’s reverse causality. Having a large chunk of the population in prison will affect the murder rate. What we really want on the x-axis might be some measure of the homicides we would get if no one were in prison. Maybe this latent measure would put the US more to the right and closer to the trendline—it depends on how effective the each country is at catching murderous people, which seems hard to know.

Another way out for them is that maybe all the countries with similar homicide rates should imprison people as much as the US, but their institutions don’t function well enough.

Here’s a simple way this could be. First, it seems generically true that incarceration should increase until the marginal costs equal the marginal benefits—people just debate these quantities. Next, just suppose that US courts are especially good at convicting the guilty party, but in the other countries with similar homicide rates (which tend to be poorer) the courts are way less likely to have the right defendant. This kind of ineffectiveness in the criminal justice system would lower the marginal benefits of incarcerating someone without affecting the marginal costs (it’s still one person having to suffer through prison). In this case, poorer countries with the same homicide rate should have much lower incarceration rates but would optimally increase them if their institutions were as good as in the US.

All the data and code used for this is available here.

Notes:

After writing this I found this article with a similar graph from Tapio Lappi-Seppälä that shows that, using victimization rates on the x-axis, the US is once again a huge outlier.

I’m sure plenty of academic papers exist that do this better and in more detail, I’ll update this post as I find out about them.

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When looking at homicide rates it's worth remembering that a good healthcare system reduces the rates as it's able to help people who get shoot survive that would die if the healthcare system isn't as good.

Initially I thought this wouldn't have much of an effect. However a brief check suggests that only ~1/3 of gunshot victims actually die in the US (study) so there's plenty of scope for healthcare to be making a significant difference. 

That makes sense. So I guess a correction where we assumed all countries had US-level healthcare would scoot the poorer countries to the left in the scatter plot...I think this could dampen trendline but would still leave the US looking pretty weird.

I also think it would still leave the US as an outlier but not as extreme as the plot currently suggests.

To a reasonable approximation, unusually high US crime rates are unusually high homicide rates[*]. Other kinds of crime are average for a wealthy country. Burglary is slightly lower.

The second anomalous thing about the US is the very high rate of gun ownership. Whilst advanced emergency room technology can be expected to lower the rate of successful homicide, all other things being equal, the availability of killing technology would increase it.

The third anomalous thing about the US is the high incarceration level. The prison population, anywhere, is the product of sentence length and incarceration rate (itself a product of crime rate and successful prosecution rate). Things like three strike rules guarantee long sentences for minor offences.

[*] "However, some countries such as Canada have similar definitions of what constitutes a violent crime, and nearly all countries had the same definition of the characteristics that constitutes a homicide.[citation needed] Overall the total crime rate of the United States is higher than developed countries, specifically Europe, with South American countries and Russia being the exceptions.[43] Some types of reported property crime in the U.S. survey as lower than in Germany or Canada, yet the homicide rate in the United States is substantially higher as is the prison population" WP

Related to this is that so far we’ve basically taken the homicide rate as exogenous, but of course there’s reverse causality. Having a large chunk of the population in prison will affect the murder rate. [...] Another way out for them is that maybe all the countries with similar homicide rates should imprison people as much as the US, but their institutions don’t function well enough.

Note that some people make the reverse argument: that a high imprisonment rate makes things worse, especially if the sentences are long and prison conditions are harsh and tending towards punishment rather than rehabilitation. People in prison end up socialized into interacting with other prisoners, which gets first-timers into a stronger criminal mindset. Once they get out, they might not have many opportunities available other than going back into crime.

At least this article notes that e.g. Finland has a low incarceration rate as well as a low recidivism rate, though the report that it cites for the recidivism figure explicitly concludes that the rates are not directly comparable between countries, so take that with a grain of salt.

Crime is a social construct shaped by laws (also constructed) and police actions (collectively an expression of the sociopolitical zeitgeist). If our crime rate is high, it's because we've constructed crime in such a way as to make it so.

Crime does not require incarceration. There are huge swaths of history where basically the only thing that would get you thrown into prison was failure to pay your debts. Or having severe mental illness, but they didn't usually call that prison. Granted, the state often killed people under those systems, but I think we can do better than that if we make it our goal.

Any given prison has a subset of these three purposes:

  • Protecting the prisoner and the public from each other
  • Rehabilitating the prisoner
  • Punishing the prisoner

The fewer purposes an institution tries to fulfill, the more successful it is likely to be. The current prison system in America is a muddled mess of all three. Just stop a random small group of friends and ask them what prisons are for; they'll probably argue about it for a long time if experience is any judge. If we could pick an actual single purpose for the prison system, I'm betting it would be better than it is now just for that, and a large number of current prisoners would no longer qualify for the "program".

Huh... unexpectedly detailed opinions on this one. ¯\_(ツ)_/¯

There's a fourth purpose with deterence. 

I've heard that, but I've never come across any convincing evidence that it works. Rather the opposite if I remember correctly: people generally don't seem to commit criminal actions out of disrespect for the law, which is the motivation a deterrent would be addressing most. I fully agree, though, that people would likely bring deterrence up if asked what prisons are for.

When looking at a source like https://nij.ojp.gov/topics/articles/five-things-about-deterrence it seems that some people mean with deterence what I would mean with rehabilitating.

I see rehabilitating as the prison sentence interacting with the person in a way that they won't commit crimes after getting out of prison.

When I speak about deterrence then I don't mean the effects of a prison sentence on the further crimes that the person commits but the effects of possible getting a prison sentence.

For that deterrence the anticipated likelihood of getting caught seems to be more important then the penalty when being caught. 

The NIJ paper (created under Loretta Lynch) first says:

Prisons are good for punishing criminals and keeping them off the street, but prison sentences (particularly long sentences) are unlikely to deter future crime. Prisons actually may have the opposite effect: Inmates learn more effective crime strategies from each other, and time spent in prison may desensitize many to the threat of future imprisonment.

Then later it says:

Studies show that for most individuals convicted of a crime, short to moderate prison sentences may be a deterrent but longer prison terms produce only a limited deterrent effect. 

It seems to me that US prisoners are very bad at rehabilitation but that people do not want to go to prison and will avoid actions that they think will likely bring them into prison. 

people generally don't seem to commit criminal actions out of disrespect for the law,

I'm not sure what you mean with that. If you mean that most of the time people don't violate the law for the sake of violating the law, that's likely true even when they are cases where it's part of the point as a mafia member getting his buttons after killing a person and thus proving that they are not a cop.

I have heard an account of an ex-gangster person that they rather go out with Brass knuckles then with a knife because they are okay with the prison sentence they would get after fighting someone with the brass knuckes and not the sentence they would get for knifing someone. 

I also heard accounts that the RICO acts worked to get mafioso to turn on the mafia because the mafioso would be okay with serving 8 years and then get out but not with serving 30 and thus the police got enough mafioso to turn to make a significant dent in the influence of the mafia. You can fill this either as deterrence or as a new class of creating bargaining chips. 

Despite/due to mandatory minimum sentencing, US prisons are full of people who got arrested for (e.g.) having an ounce of pot in their car during a "routine" traffic stop (whatever that is). Just having a law on the books seems to do very little to change the behavior of individuals.

Now, people don't just keep pot in their cars because they're thinking something like "they'll never catch me", in conscious defiance of the rule of law. Nor are they especially worried about what would happen to them if they did get caught. The potheads I know usually turn out to have pot in their cars because they want to smoke/eat the stuff and their home is a long way from their dealer and they had to work that day and they forgot it was in there so it's been there for a week and now the whole car smells like it. They don't usually even seem to think about the legality of their hedonic pastimes at all; they just likes pot and know where to get it.

This behavior is not consistent with prison time being an effective deterrent.

If someone commits a crime because they forgot something that's qualitatively different then crimes that do require more intent to be committed. 

Just having a law on the books is not enough to deter crime. You actually need for the people who might commit the crime to expect that there's a reasonable chance to be caught. 

True enough, and there's a slippery slope to a police state in that observation. That's part of the problem, actually: some neighborhoods are much closer to being in that police state than others. Presumably, just as much extralegal activity happens in other places, but we (society) systematically fill jails from these heavily policed areas. Looking back to the original question, I'd say that this suggests crime does not fully "explain the exceptional US incarceration rate". You need to write laws in a particular way and establish at least a partial police state to get that much of your population in jail.

I think your argument is interesting, but doesn't make sense in the context of this article. The author is using homicide as their proxy for crime, and homicide is the prototypical example of something which is always a crime (although there's some variation in who can get away with it and what the punishment is).

(Also while it's true that homicide was historically not punished by prison very often, your second paragraph dances around the fact that that's because the punishment was worse - death)

The work OP did in the update does use homicide as a proxy for crime, but still finds that the US is "an enormous outlier" in the world when comparing homicide rates with incarceration rates. We also see enormous imbalances along (socially constructed) racial lines with regard to arrest rates, convictions, and sentencing, implying that the state of our prisons has little to do with "crime rates" as such.

Another way out for them is that maybe all the countries with similar homicide rates should imprison people as much as the US, but their institutions don’t function well enough.

I'd be interested to see more analysis of this hypothesis. It seems quite likely to me that the US having an unusual combination of violence and competence is at least part of the explanation for the high incarceration rate. Would be curious to know how much.

Maybe a simple follow-up analysis would just be to check the ratios of homicides to people-in-prison-for-homicide for various countries (rather than comparing against incarceration rate more generally). Would be interesting to know on a crime-by-crime basis how the US compares to other countries.

I really want to try this...From a few minutes of googling it seems pretty hard to find this info for other countries. Will update if I'm able to cobble the data together.

I think that you would have to only consider countries that have similar suicide rate as well as conviction rate, as I've heard that some countries (Japan) rule every unsolved homicide as suicide to have a perfect police track record.

I am not qualified to estimate if it's true but that's something else to consider.

You can get a complementary analysis by comparing the US to its past self. Incarceration rate, homicide rate. Between 1975 and 2000, the incarceration rate grew five-fold while the homicide rate fell by half.

That analysis doesn't tell you whether growing the incarceration rate was necessary to deal with the high homicide rate and get it to fall in half. 

You could get that by comparing with other countries that reduced their homicide rates by similar amounts over similar timescales.

Out of interest, what is the reasoning behind using homicide rates as a proxy for crime more generally? Countries with (relatively) high rates incarceration for non-violent drug offenders might skew the relationship (Thailand for example).

There is then a second question about whether or not non-violent drug offenders should be imprisoned (at all/at the rates that they are in some countries), but the argument that incarceration is explained by crime might hold in these countries.

The general reasoning is that homicide generally makes it into the official statistics while a lot of other crime doesn't always get reported. 

It's not intended as a proxy of what a society criminalizes but a more cultural independent notion of crime.

Thanks for the clarification !

Good question--my reasoning was that homicide is well-measured and easy to find online, and should correlate with levels of crime more broadly. I wonder what variable we would want to address the Thailand issue...maybe the share of prisoners who are "violent" would be useful, but I'd be surprised if I could find it for many countries.

I don't see why one thinks homicide is a good proxy for crime in general. I wonder if a different approach here might be simply focusing on homicide and incarceration to see if that sheds any light.

I didn't do much research into other cross-country crime measures so I'm definitely curious to learn more about other ways of getting at this. 

But to me the most obvious reason to favor homicide is reporting. Partially because it's fresh in my mind, I'd recommend The Challenge of Crime in a Free Society (from 1967). Starting at page 25 they go through changes in reporting that caused huge blips in measured crime in the US. I think the authors may have wanted to play down the crime increase for political reasons, but even discounting them somewhat they do identify issues in measurement that could easily persist today and be way worse in other countries.