National Edition

What explains falling crime rates?

Published: Tuesday, Aug. 13 2013 6:00 a.m. MDT

A prison guard places an inmate in solitary confinement at the Beto Unit prison in Tennessee Colony, Texas, in this 2001 file photo. Crime rates have been decreasing over the past 25 years, but there is no consensus on why.

LM Otero, Associated Press

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Extensive media coverage of the George Zimmerman trial, the rash of homicides on Chicago’s South side and the mass shooting at Sandy Hook Elementary school in Connecticut could leave the public with the perception that America is becoming an increasingly dangerous place.

Though this may seem like a reasonable conclusion, it's not how the facts shake out.

Crime rates have been going down for the last twenty years, according to figures released earlier this summer from the Bureau of Justice Statistics. Gun-related murders, for example, declined 39 percent between 1993 and 2011, while nonfatal gun crimes dropped 69 percent during the same period. Crimes committed by strangers have dropped 77 percent since 1993, while crimes committed by offenders known to the victim decreased 41 percent.

While the numbers make it clear that crime is going down, there is no consensus as to why. Any number of things could be going on, said Alfred Blumstein, professor of public policy at Carnegie Mellon University in Pittsburg. Some theories include higher rates of incarceration, reductions in exposure to lead, legalization of abortion and the stabilization of the crack cocaine market. Blumstein argues that these explanations apply only to reductions in crime between 1993 and 2000.

Higher rates of incarceration

The United States has one of the highest incarceration rates in the world. Nearly seven million adults, or 3 percent of the population, were under correctional supervision (jail, prison, probation or parole) in 2011, according to the Bureau of Justice Statistics.

Part of the reason America has such a high rate of people behind bars, experts say, are the nation's harsh sentencing policies. These include mandatory minimum penalties, three strikes rules and habitual offender rules, according to Nicole Porter, of the the Washington D.C.-based Sentencing Project, a nonprofit organization which advocates for reforms of sentencing policy.

While some, including experts like Porter, suggest that high incarceration rates represent both a miscarriage of justice and a significant financial burden on taxpayers, others argue these policies have made America a safer place. For example, a study from The Heritage Foundation, a conservative think tank based in Washington D.C, concluded that putting so many people behind bars has removed a criminal cohort from the streets and reduced crime.

Critics of this explanation argue that there isn’t a perfect relationship between crime and punishment. “Incarceration was growing in the late 1980’s which is when crime was also increasing,” Blumstein said.

America unleaded:

One of the newest explanations for the precipitous drop in crime over the last twenty years was outlined in a recent article for Mother Jones, a left-leaning national news magazine. In the piece the author Kevin Drum documents the well-established relationship between lead exposure and brain development, which is that lead exposure in small children is associated with many complications later in life, including lower IQ, hyperactivity, behavioral problems, and learning disabilities, and likelihood to take part in criminal activity.

Research done by Jessica Reyes, a professor of public health policy at Amherst College, shows a convincing relationship between lead exposure and crime. Reyes discovered demand for leaded gasoline declined unevenly in states around the country beginning in the 1970's, with some states banning leaded gasoline early while others continued selling the product well into the 1980’s. She found that in states where consumption of leaded gasoline declined slowly, crime declined slowly. Conversely, in states where it declined quickly, crime declined quickly.

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