After rising for decades, violent crime across the U.S. began a material decline starting in the early 1990s. In 1991 there were 758.2 reported violent crimes per 100,000 people and by 2018 it had dropped 368.9 per 100,000 people. A 52% drop!

The drop in crime has been universal. It has dropped in urban as well as rural areas. It has dropped in major metropolitan areas and smaller cities. Violent crimes have dropped as have property crimes.

Interestingly, public perception of crime has often been at odds with the data as most people generally feel as if crime has gotten worse:

Why has the crime rate dropped? There have been many proposed reasons including the “Broken Windows Theory,” increased numbers of police and the reduction of crack use.

Another theory is that the reduction in childhood lead exposure contributed to the drop in crime. In the early 1970s, hundreds of thousands of tons of lead were emitted each year by cars in America. In the late 1970s The Clean Air Act mandated the removal of lead from gasoline and by the 1990s it had been completely removed. As lead was removed from the atmosphere, lead levels in children’s bloodstream dropped as well. This drop in lead in children’s blood has resulted in increased IQs and lower rates of mental retardation.

Not only does lead negatively affect IQ, but it also can “result in behavioral changes, including a shortened attention span, promotion of hyperactivity, increase in impulsive and anti-social behavior and generally reduced overall performance.” Source. As such, “Childhood lead exposure can lead to psychological traits that are strongly associated with aggressive and criminal behavior.” Source. Since phase-out of lead in gasoline occurred at different rates in different states, researchers have been able to determine the extent to which reduction of lead exposure in childhood explained violent crime. Economist Jessica Wolpaw Reyes of Amherst College concluded in a seminal study that:

These results suggest that childhood lead exposure is significantly associated with violent crime. Based on these estimates, the fall in gasoline lead would be responsible for a 56% drop in violent crime between 1992 and 2002. These results also imply that abortion legalization was responsible for a 29% drop in violent crime between 1992 and 2002.

Another study similarly found that:

Preschool blood lead trends also appear to explain most of the substantial variation in property and violent crime rates in the USA, Canada, Britain, Australia, New Zealand, West Germany, France, Italy, and Finland across several decades. Crime rates track blood lead with similar time lags within each nation, consistent with neurobehavioral damage in the first year of life: A 23-year lag for violent crime, consistent with the typical age of violent offenders, and an 18-year best-fit lag for burglary, consistent with the typical age of property crime offenders.

Did you notice that the Amherst study also attributed the drop in crime to abortion legalization? This theory is also championed by economist Steven Levitt of the University of Chicago. He similarly has found that a material factor in the drop in crime is due to the legalization of abortion. How can that be? “The underlying theory rests on two premises: 1) unwanted children are at greater risk for crime, and 2) legalized abortion leads to a reduction in the number of unwanted births.” Source. Like with the lead study, Levitt looked at state data. Five states had legalized abortion prior to Roe v. Wade. Looking at future crime rate declines in the states where it was already legal versus states where it was only legal after 1973 supported the conclusion that legalizing abortion led to crime decreases about 15-20 years later. Interesting.