The factors that have caused an increase in prison populations
in the United States are-
- Crime rates have risen and fallen independently of
incarceration rates. Crime rates began rising
in the early 1960s, roughly a decade before incarceration rates
did. In the 1980s, violent and property crime rates fluctuated,
while incarceration rates continued rising. By the end of the
1990s, crime rates had fallen to 1970s levels, and they have
continued to fall throughout the 2000s; yet incarceration rates
continued to grow well into the 2000s, peaking in 2007 .
- Arrests per crime have been relatively stable.
Incarceration rates may rise even when crime rates remain stable if
police become more effective at apprehending offenders. Yet, “by
the measure of the ratio of arrests to crimes, no increase in
policing effectiveness occurred from 1980 to 2010 that might
explain higher rates of incarceration,” a recent National Research
Council report concluded.
- The share of offenders sent to prison has climbed
dramatically. For all major crime types, the likelihood
that a person convicted of a crime will go to prison has risen
sharply over the past 30 years. That’s especially true for drug
offenses; the likelihood of being sent to prison for a drug-related
crime rose by 350 percent between 1980 and 2010. The
increase in the share of offenders sent to prison accounts for 44
to 49 percent of the long-term growth in state incarceration rates,
the National Research Council study estimated.
- Length of stay in prison has grown for all types of
crimes. Between 1990 and 2009, the average time served
rose by nearly 25 percent for property crimes and by roughly 37
percent for violent and drug crimes, the Pew Center on the States
estimates. The increase in average sentences has contributed as
much to the growth in incarceration rates as the rise in the share
of offenders sent to prison, and possibly slightly more.