CRIME RATESincidents of a specific type, the third column re-
ports the rate per 100,000 residents, and the final
column indicates the change in the rate over a ten
year period. In 1997, for example, 1,634,770 vio-
lent crimes were known to the police. The rate of
violent crimes was 610.8 per 100,000 persons,
which represents a decrease in the rate of violent
crimes from 1988 to 1997 of 4.1 percent. Officially
reported crime rates fell in all Part I categories
from 1988 to 1997.
Crimes reported or discovered by the police
and found through investigation to have occurred
are labeled ‘‘crimes known to the police.’’ A crime
found not to have occurred is ‘‘unfounded,’’ and
does not appear as a crime known to the police.
Although occasionally police discover a crime be-
ing committed (e.g., they happen upon a burglary
in progress, or they arrest someone for resisting a
police officer) they are highly dependent on citi-
zen reports of criminal incidents.
The UCR also provides data on arrests for
Part I and Part II crimes, and reports these crimes
on the basis of the geographical divisions described
above. Since these data are for arrests, the rates
calculated from them should be labeled ‘‘arrest
rates.’’ Part II crimes include: other assaults (not
including aggravated assaults), forgery and
counterfeiting, fraud, embezzlement, stolen prop-
erty (buying, receiving, and possessing), vandal-
ism, weapons (carrying, possessing, etc.), prostitu-
tion and commercialized vice, sex offenses (except
forcible rape and prostitution), drug abuse viola-
tions, gambling, offenses against family and child-
ren, driving under the influence, liquor law viola-
tions, drunkenness, disorderly conduct, vagrancy,
curfew and loitering law violations, and runaways.
National Crime and Victimization Survey
(NCVS). The NCVS data come from large surveys
using probability samples of respondents. Since
1973 a national-level program has surveyed a proba-
bility sample of U.S. households. The U.S. Census
Bureau conducts the survey, and during the 1990s
the sample contained some 60,000 households
and approximately 100,000 respondents. The re-
sults of this survey have been published annually
since 1973 by The U.S. Department of Justice in
Criminal Victimization in the United States.
The NCVS collects data on a much smaller
number of crimes than the UCR. Since it is a
survey of the victims of crime, it does not record
homicides, but it does record forcible rapes and
sexual assaults, robberies, aggravated assaults, sim-
ple assaults, burglaries, larceny-thefts, and motor-
vehicle thefts. It also provides details about the
victims of crime not available in the UCR. These
include the household income of the victim, any
injuries sustained by the victim, insurance cover-
age, length of any hospitalization due to injuries,
what protective measures the victim employed,
and so on.Careful field-testing preceded the initiation of
data collection for NCVS in 1973 and before any
changes made to its design since that time. An
early decision involved the length of the reference
period (the period the interviewers referred to
when they asked whether victimizations occurred
during the past period). Researchers chose a six-
month reference period on the basis of the costs of
doing more frequent surveys and studies that
showed the effect of memory decay on remember-
ing whether an event occurred. Respondents tend
to telescope events into the reference period, and
this can cause substantial increases in the number
of victimizations reported during the past six
months. To overcome this problem, each respon-
dent remains in the sample for three years with
interviews repeated every six months. Victimiza-
tions reported to the interviewer the first time a
respondent is interviewed do not contribute to
estimates of the crime rates. That first interview
and subsequent interviews provide bounds for the
six-month reference period. The interviewer asks
about victimizations occurring since the last inter-
view and has a list of incidents reported in the last
interview to make sure that those incidents are not
telescoped into the reference period.To estimate rates for the entire nation from
the NCVS data, researchers use the samples to
estimate the number of victimizations occurring in
the entire nation. They then use these estimates to
calculate victimization rates. The derived estimates
often contain large sampling errors, since they are
based on only a ‘‘small’’ sample of the total popula-
tion of the United States. These large sampling
errors are greatest for the crimes least frequently
reported by the respondents, for example, victimi-
zation rates for rapes involve more sampling error
than rates for aggravated assault (O’Brien 1986).