The District [of Columbia] is on track to have fewer killings than in any year since 1964, when the population was about 760,000 and Vietnam War protests were just beginning. . . . In 1991, the District was known as the murder capital of the United States, recording 479 that year. This year, there have been 79.
From the Washington Post via the Sentencing Law and Policy blog.
Also notably, from the same source:
Criminologists . . . agree that the common belief that crime is connected to the economy is false. . . . crime doesn't automatically go up when the economy is poor. . . . Criminologists point to the Great Depression in the 1930s as a time of relatively low crime compared with the Roaring Twenties, when the country experienced more violence.
This is despite the fact that unemployment was close to zero in 1929, and while it was above 10% for most of the Great Depression and peaked at close to 25%.
Then again, while the murder rate, for example, did go down during the Great Depression, it did so only after peaking in 1933 (and continued to fall until about 1955), after steadily rising since about 1903 or 1905. Murder rates started to rise again around the time the Vietnam war started and continued to rise for its duration. The current drop in murder rates has still not returned murder rates to below their pre-Vietnam era trough.
The existence of a broad national trend also tends to disprove the suggestion, common in law law enforcement, that smart local policing is responsible.
Theories based in changing demographics, abortion, reduced use of lead paint, or total institutionalization rates, all of which are what Bernard Harcourt has described as "social physics," by which he means "social theories that are necessarily true as a result of the physical nature of our mortal existence, in contrast to theories that depend on the intermediation of human consciousness and decision-making," seem to be a better fit for the data. Theories like "(1) rational choice theory, (2) the broken-windows theory, (3) legitimacy theory," seem to fit the data less well.
Harcourt claims that the correlation is robust (the period of declining murder rates had low rates of penal imprisonment but much higher rates of mental health institutionalization than we do now), despite the "perplexing" fact that "the populations in asylums and prisons were very different: residents in mental hospitals were more white, female, and older than our current prison populations. In 1966, for example, there were 560,548 first-time admissions to mental hospitals, of which 310,810 (55.4%) were male and 249,738 (or 44.6%) were female. In contrast, new admittees to state and federal prison were consistently 95% male throughout the twentieth century. There were also sharp differences in racial and age compositions." According to his research, the "correlation between the aggregated institutionalization and homicide rates is remarkably high: -0.78. . . . aggregated institutionalization is at least two times more influential than unemployment. . . . In all but one case, it is statistically significant at the .001 level (and that one case is significant at the .002 level)[.]"
Harcourt makes a somewhat more philosophical examination of the same data here; the money chart is on page six. On the next page he also notes (emphasis added) that "In more technical research (Harcourt 2006), I test and quantify the relationship, and find that . . . holding constant the leading structural covariates of homicide (poverty, demographic change, and unemployment),the relationship is large, statistically significant, and robust." The strong relationship between both poverty and unemployment and the murder rate makes its lack of strong cyclical trends particularly puzzling. One historical footnote notes that 17th century France didn't bother to distinguish between criminals and those who were mentally ill or simply needy.
One possibility that the both mental hospitals and prison populations are grossly overinclusive of people who don't need to be institutionalized, but that higher institutionalization rates reflect times when the threshold of deviant conduct necessary to cause one to be institutionalized was low enough to include a large share of all people who really do present a risk of committing serious crimes in the future.
For example, while a large share of people who are involved in the illegal drug scene may be mostly harmless, it may be that a very large share of potential criminals are involved in the illegal drug scene and were immobilized by the war on drugs. Similarly, while very few of the mentally ill are psychopaths, those few may do disproportionate harm if they are not institutionalized.
If so, the really hard question is whether it is possible in practice to be more selective in who we incarcerate in a way that accurately discriminates between those likely to commit crimes in the future, and those unlikely to do so.
I'd like to think that empirical research, modern statistics, improved social science research methods, a better fundamental understanding of the human psyche, and more than a century of diligent criminology could achieve this seemingly modest goal. Even cutting the "false positive" rate by 50% would end an immense amount of human waste and suffering, and would also greatly ease a burden on the public purse. But, are we really that much more clever than people were two generations ago?
An alternate explanation of the link between total incarceration rates and crime rates is that they reflect a general societal intolerance for deviance. They may be a sensitive symptom of the spirit of the age, rather than its cause. If so, more discriminating incarceration and increased judicious use of mental health institutionalization may miss the point entirely.
Yet a third way to explain the impact of incarceration is as a form of welfare, rather than a form of restraint. People incarcerated in total institutions have their basic needs provided for by someone else. Prison is a package that includes food, shelter and health care. Hence, institutionalized people have far less of a need to commit economic crimes or crimes that are related to economic crimes or needs. It isn't as if institutionalized people are completely incapable of committing crimes that contribute to the murder rate -- prison inmates kill each other with disconcerting regularity. Harcourt also notes that in 17th century France, according to Foucault, at least, it was the inmates who complained about their mentally ill institutional companions, and not the other way around.
Or perhaps, in a variant on the welfare hypothesis, the economy has only a certain number of jobs that marginally economically able people can fill. Most jobs require consistently high levels of "normal" social interaction. Total institutions allow a large sharer of the marginally economically able who are not institutionalized to find employment. While someone with a severe mental illness and someone who has difficulty refraining from committing crimes have far different levels of culpability in our society, both are as a result less able to earn a conventional living in our economy. Indeed, modern psychiatry expressly defines difficulty in functioning as a necessary symptom to diagnose most mental health conditions; if you can cope well with your life in the absence of mental health treatment, you are, by definition in most cases, not mentally ill. In this view, mental health commitment reduces crime because it frees up deviance tolerant jobs for would be criminals, not because those confined were any more likely to commit crimes.