http://bactra.org/weblog/algae-2012-03.html#zimring ( )

During the 1990’s the United States saw an unprecedented decrease in crime. Nationwide there was an approximately 40% decrease in all seven of the FBI’s Uniform Crime Reporting (UCR) categories. Police departments across the nation have taken credit for the decreasing crime in their jurisdictions and scholars of various disciplines have tried to find their own answers for the decline. In The Great American Crime Decline, Professor Franklin E. Zimring, of the University of California, Berkley, School of Law, has summarized the most popular explanations in an attempt to determine what really happened and why.

Professor Zimring looked at six widely held explanations for the crime decline. These were divided into two categories. The first contains factors that have long been used to explain crime increases and decreases – incarceration, demography, and economic conditions. The second are those explanations which were created in a specific attempt to explain the events of the 1990s.

The first category was ideally situated to explain the crime decreases of the 1990s. Incarceration rates were at an all time high, the percentage of population made up of high-crime aged youths had dropped, and the economy continually expanded during the ‘90s. Even though common sense might tell you that these were good explanations of the crime decrease, Professor Zimring does not entirely agree.

Professor Zimring found possible causes for some of the ‘90s crime decline amongst the above explanations. However, it only amounted to between 15% and 50% of the decline, depending on which studies you agree with. I would tend to agree with the low number just to be on the safe side, but for the sake of argument I will split it down the middle and go with 32%. That still leaves a major portion of the decline to be explained by the second category, explanations that were created after the decline because they fit the results. The three theorized causes in the second category were police, the decline of crack cocaine, and the increased access to abortion.

Professor Zimring has shown that none of the explanations offered served to explain the over 40% crime decline during the 1990s. This has not stopped government, police departments in particular from claiming their actions were responsible. A large portion of the decrease was probably the consequence of cyclical forces beyond the existing ability of social science to explain.

If you have an interest in policing or crime this is an interesting work. If not you might find it a bit dull. It was a little heavy on the statistics but if you know what a regression is you’ll be OK, if you don’t you’ll probably be OK you just need to gloss over a few parts. I found one of the most interesting parts to be the refutation of Steven Levitt’s theory, that he put forth in Freakonomics, that Roe v Wade was responsible for the ’90’s crime decrease. ( )