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What explains falling crime rates?

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

Blumstein acknowledges the creativity of this theory, but said that just because lead emissions and crime rates have the same downward trend doesn’t mean that one caused the other; correlation is not causation. “It's hard to say whether it was lead exposure causing the higher rates of crime or if it was poverty or drugs,” he said.

Roe v. Wade

University of Chicago economics professor Steven Levitt and New York Times journalist Stephen Dubner popularized the idea that crime reductions in the 1990’s were a result of increased access to abortion after the 1973 Supreme Court decision in Roe v. Wade.

Their theory is based on two assumptions: first, legalized abortion leads to fewer "unwanted" children and second, unwanted babies are more likely to suffer abuse and neglect, increasing their risk for criminal behavior later in life. “The first assumption, that abortion reduces the number of unwanted children, is true virtually by definition. The second assumption, that unwanted children are at increased risk for criminal involvement, is supported by three decades of academic research. If one accepts these two assumptions, then a direct mechanism by which the legalization of abortion can reduce crime has been established,” wrote Levitt.

Using statistical data, Levitt and Dubner estimate that as much as one-half of the decline in crime in the 1990s is due to legalization of abortion.

Other researchers are skeptical of Levitt and Dubner’s conclusion. “It’s a very clever way of explaining the trend, but ultimately it doesn’t have a lot of explanatory power,” Blumstein said. He believes that if this explanation were true, the effects would show up in other places, for example decreased school drop out rates, teen pregnancy, and even academic performance. But there is absolutely no relationship, he said.

Another factor for which Levitt and Dubner didn’t account, according to Blumstein, is the fact that although abortion wasn’t legal prior to 1973, people still got them. “It could be the case that people who were going to get abortions would get them whether it was legal or not,” he said, a consideration which significantly diminishes the explanatory value of Levitt and Dubner's hypothesis

Crack goes flat

Blumstein’s preferred explanation for the 1993 to 2000 drop in crime is related to the decline of demand for crack cocaine. Between 1986 and 1993 demand for crack — a more potent mixture than regular cocaine — exploded, particularly among African-Americans. Crack was sold on the street so if drug deals went bad the violence would be visible, he said. As a consequence, law enforcement cracked down on this market, instituting harsh penalties for those found in possession of the substance. Five grams of crack would land a person in jail for five years. By contrast a person would have to be carrying 500 grams of regular cocaine to receive five years in jail. Harsh penalties may have deterred people from getting involved with the drug.

As the epidemic went on it became clear what crack did to users: short highs and crushing lows, hallucinations, irritability and paranoia. “Demand for the drug went down because potential users, the kids and grandkids of people on crack, saw what the drug did to people and stayed away,” Blumstein said.

The Obama effect

Criminologists expected the crime rate to go up significantly in 2009 because of the great recession, and as Blumstein points out, “we tend to expect crime to rise in a bad economy.” But that isn’t what happened. Crime actually went down nearly ten percent that year. By 2010 things had stabilized with crime falling again between one to two percentage points a year.

None of the explanations for the reductions between 1993 and 2000 make sense for 2009, according to Blumstein. “Those phenomena were all gradual so we’d expect to see gradual reductions like we did between 1993 and 2000,” he said. Crime just plummeted in 2009. Whatever caused it is likely a discrete event, not a policy change, he said.

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