UNDER THE MICROSCOPE: The last two decades of the 20th century saw a dramatic decline in crime rates in the US. Criminologists and sociologists have attempted to explain the statistics, but no single theory fully accounts for the phenomenon. Richard Rosenfeld tells the story in the February 2004 edition of Scientific American, writes Prof William Reville
According to the FBI, which compiles statistics of serious violent and property crime, the US homicide rate rose from 8.0 per 100,000 people in 1983 to a peak of 9.8 in 1991. It then fell to 5.5 per 100,000 people by 2000: a 44 per cent decrease. Between 1991 and 2000 burglaries also fell by 42 per cent, and robberies - thefts accompanied by force - dropped by 47 per cent.
When the statistics are broken down by age it becomes clear that the US experienced two drops in crime between 1980 and 2000. One was among adolescents and young adults (under the age of 25), the other among adults. The rate of homicide among adults has steadily declined since 1980. Youth homicide levels increased dramatically between 1980 and 1993, however, then fell equally dramatically. Robbery rates among adolescents and young adults showed the same profile.
The rise of youth violence in the 1980s and its decline in the 1990s were highly concentrated among young black men. The homicide rate grew fivefold among black male adolescents from 1984 to 1993 and more than twofold among young black male adults. It fell rapidly soon afterwards. The changes for young women and whites were much less pronounced. The homicide rate among black men more than halved between 1983 and 2000. The homicide rate for young Hispanic males mimicked the trends for young black males, but less dramatically. The rise in youth homicide and robbery rates during the 1980s, and its later decline in the 1990s, happened earlier in the larger cities.
During the final two decades of the last century there was a proliferation of firearms possession among young minority males, and nearly all the growth in youth homicide rates during the 1980s and early 1990s involved handguns.
Many explanations have been proposed to explain the rise and fall in youth violence and the general decline in adult violence over the past 20 years. No explanation accounts for all the facts and some explanations are clearly wrong. The demographic explanation predicts, for example, that, as a greater proportion of adolescents and young adults are involved in homicide and other crimes than adults, crime rates will shrink when the younger segment of the population shrinks and grow when that segment grows. But the relative number of 14- to 24-year-old black males, the group at highest risk, changed little from 1993, the peak of youth violence, to 2000, its trough.
Another explanation attributes half the decline of the 1990s to the legalisation of abortion in the 1970s. Because there were fewer unwanted children among low-income women, this prevented the crimes those disadvantaged children would have committed 15 to 20 years later. This explanation may be partly right, but no more than that because, if fully correct, the youth-homicide trends would have lessened earlier than they did.
More efficient policing regimes have also been invoked to explain the crime statistics. Policing procedures were revised in many cities during the 1990s, but many of these changes did not begin until well after the decline in crime had begun. Also, the decline was noted in many cities that had not revised their policing.
One hypothesis that has a lot going for it is the crack-cocaine explanation. Cheap crack cocaine became very popular during the 1980s. Drug dealers recruited inner-city youths to sell it, to meet growing demand, arming them with handguns for protection against thieves and rival sellers. There was a corresponding surge in gun violence.
For some reason crack turned out to be a one-generation drug. The original addicts, who stopped taking the drug or died, have not been replaced by new crack addicts, as younger users prefer marijuana. As demand for crack declined, so did the handgun-backed youth violence that accompanied its rise. The crack hypothesis accounts nicely for the timing and ethnic characteristics of the youth-violence phenomenon.
Another hypothesis proposed to account for the drop in crime during the 1990s is the acceleration in incarceration rates. Between 1980 and 2000 the US prison population quadrupled. This may also have contributed indirectly to the youth-homicide epidemic, however. As demand for crack increased during the 1980s, drug dealers increasingly turned to younger sellers, as more and more adult vendors were being imprisoned.
To me the crack-cocaine hypothesis has the ring of truth to it. Anyone who has lived in the US is familiar with its enormous socio-economic contrasts. Affluence and opportunity are plentiful, but there are also pockets of poverty and deprivation on a scale no longer seen in the welfare states of Europe. Many big city ghettos fall into this latter category, and it is easy to visualise how changing patterns of supply and demand in the drugs trade could quickly rewrite crime statistics.
- William Reville is associate professor of biochemistry and director of microscopy at University College Cork