U.S. Department of Justice
Office of Justice Programs
Bureau of Justice Statistics                                                   
                
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Note to readers of the ASCII version:
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This file contains the following:

-- Survey Methodology for Criminal Victimization in United States
-- Computation and Application of Standard Errors
-- Number of households and persons interviewed by year
-- Glossary
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May 2000, NCJ 184957                                                           
                    

Survey Methodology for Criminal Victimization 
in the United States

The survey results contained in this report are based on
data gathered from residents living throughout the United
States, including persons living in group quarters, such as
dormitories, rooming houses, and religious group dwellings. 
Crew members of merchant vessels, Armed Forces personnel
living in military barracks, and institutionalized persons,
such as correctional facility inmates, were not included in
the scope of this survey.  Similarly, U.S. citizens residing
abroad and foreign visitors to this country were excluded. 
With these exceptions, individuals age 12 or older living in
units selected for the sample were eligible to be
interviewed.                                 

Data Collection

Each housing unit selected for the National Crime
Victimization Survey (NCVS) remains in the sample for 3
years, with each of seven interviews taking place at 
6-month intervals.  An NCVS interviewer's first contact 
with a housing unit selected for the survey is in person. 
The interviewer may then conduct subsequent interviews by
telephone.

To elicit more accurate reporting of incidents, NCVS uses
the self-respondent method which calls for the direct
interviewing of each person 12 years or older in the
household.  An exception is made to use proxy interviewing
instead of direct interviewing for the following three
cases:  12- and 13-year-old persons when a knowledgeable
household member insists they not be interviewed directly,
incapacitated persons, and individuals absent from the
household during the entire field-interviewing period.  
In the case of temporarily absent household members and
persons who are physically or mentally incapable of 
granting interviews, interviewers may accept other 
household members as proxy respondents, and in certain
situations non-household members may provide information 
for incapacitated persons.

Some interviews were conducted using Computer-Assisted
Telephone Interviewing (CATI), a data collection mode 
which involves interviewing from centralized facilities 
and using a computerized instrument.  In the CATI-eligible
part of the sample, all interviews are done by telephone
whenever possible, except for the first interview, which 
is primarily conducted in person.  The telephone interviews
are conducted by the CATI facilities in Hagerstown, 
Maryland and Tucson, Arizona.

Sample Design and Size

Survey estimates are derived from a stratified, multi-stage
cluster sample.  The primary sampling units (PSU's)
composing the first stage of the sample were counties,
groups of counties, or large metropolitan areas.  Large
PSU's were included in the sample automatically and are
considered to be self-representing (SR) since all of them
were selected.  The remaining PSU's, called non-self-
representing (NSR), because only a subset of them was
selected, were combined into strata by grouping PSU's with
similar geographic and demographic characteristics, as
determined by the 1990 Census. 

The initial 1990 design consisted of 93 SR PSU's and 152 
NSR strata, with one PSU per stratum selected with
probability proportionate to population size.  A sample
reduction was done in October of 1996, reducing the number
of NSR PSUs by 42.  So, the current NCVS sample consists 
of only 110 NSR PSUs.  The NCVS sample design continues 
use of both 1980-and 1990-based sample through 1997. 
Beginning in 1998 only 1990-based sample remains.

In the second stage of sampling, each selected
stratification PSU is divided into four nonoverlapping
frames (unit, area, permit, and group quarters) from which
NCVS independently selects its sample.  From each selected
stratification PSU, clusters of approximately four housing
units or housing unit equivalents are selected from each
frame.  For the unit and group quarters frames, addresses
come from the 1990 Census.  For the permit frame, 
addresses come from building permit data obtained from
building permit offices.  This ensures that units built
after the 1990 Census are included in the sample.  For the
area frame, sample blocks come from the 1990  Census files. 
Then, addresses are listed and sampled in the field.

In order to conduct field interviews, the sample is 
divided into six groups, or rotations, and each group of
households is interviewed once every 6 months over a 
period of 3 years.  The initial interview is used to bound
the interviews (bounding establishes a time frame to avoid
duplication of crimes on subsequent interviews), but is not
used to compute the annual estimates.  Each rotation group
is further divided into six panels.  A different panel of
households, corresponding to one sixth of each rotation
group, is interviewed each month during the 6-month period. 
Because the survey is continuous, newly constructed housing
units are selected as described, and assigned to rotation
groups and panels for subsequent incorporation into the
sample.  A new rotation group enters the sample every 6
months, replacing a group phased out after being in the
sample for 3 years.

Selection of Cases for CATI

Currently, the NCVS sample PSU's fall into three groups of
CATI usage:  maximum-CATI PSU's, where all the segments in
the PSU are CATI-eligible; half-CATI PSU's, where half of
the segments in the PSU are randomly designated to be CATI-
eligible; and no-CATI PSU's, where none of the segments are
CATI-eligible.  The level of CATI usage for each PSU was
established with concern toward an optimal workload for the
field interviewers.  In the "half-CATI" PSU's, a random
sample of about 50% of the segments in each PSU is taken and
designated as CATI-eligible.  The sample cases in CATI-
eligible segments from the max-CATI and the half-CATI PSU's
are interviewed from CATI facilities while the other sample
cases are interviewed by the standard NCVS field procedures.


Collection Year Estimates

The data in the surveys were collected during the calendar
year being estimated.  Because of the retrospective nature
of the survey, the estimates include some incidents that
actually occurred during the previous year.  Analyses
comparing the victimization information collected in a
calendar year (termed a collection year) to that obtained
about victimizations experienced in the same calendar year
(called a data year) show only a small difference between
the two methods.  The differences will be greater during
periods of changing crime rates and less during periods of
stable rates.

Estimation Procedure

Annual collection year estimates of the levels and rates of
victimization are derived by accumulating four quarterly
estimates.  The weights of all crimes reported during
interviews in that year are summed, regardless of when the
crime occurred.  The base for the collection year rate for
personal crime is sum of all person weights.  Likewise, the
base for the property crime rates is the sum of all
household weights.

The estimation procedure begins with the application of a
base weight to the data from each individual interviewed. 
The base weight is the reciprocal of the probability of each
unit's selection for the sample, and provides a rough
measure of the population represented by each person in the
sample.  Next, an adjustment is made to account for
households and individuals in occupied units who were
selected for the survey but unavailable for interview.

In addition to adjusting for unequal probabilities of
selection and observation, the final weight also includes a
ratio adjustment to known population totals based on the
adjusted counts from the 1990 Census.  Specifically, the
final person weight is the product of the values of the
following six component weights; the final household weight
is the product of all components except the within-household
non-interview adjustment component detailed below:

Probabilities of selection 

*  Base weight: The inverse of the sample unit's probability 
of selection. 

*  Weighting control factor:  adjusts for any subsampling    
due to unexpected events in the field, such as unusually    
high growth in new construction, area segments larger    
than anticipated, and other deviations from the overall    
stratum sampling rate.

Probabilities of observation (Nonresponse)

*  Household non-interview adjustment:  adjusts for       
nonresponse at the household level by inflating the    
weight assigned to interviewed households so that they    
represent themselves and non-interviewed households.

*  Within-household non-interview adjustment:  adjusts for   
nonresponse at the person level by inflating the weight
assigned to the interviewed persons so that they represent
themselves and the missed interviews.

Post-stratification ratio adjustment to known population
totals

          The distribution of the sample population may differ
     somewhat from that of the total population in terms of
     age, race, sex, residence, and other characteristics. 
     Because of this, two stages of ratio estimation are
     employed to bring the two distributions into closer
     agreement, thereby reducing the variability of the
     sample estimates.

*  First-stage factor:  the first stage of ratio          
estimation is applied only to non-self-representing          
PSU's.  Its purpose is to reduce sampling error          
caused by selecting one PSU to represent an entire          
stratum.  It adjusts for race and zone of residence          
differences between the sample non-self-         
representing PSU's and the population non-self-         
representing PSU's. (For self-representing PSU's          
this factor is set to 1). 

*  Second-stage factor:  the second stage of ratio          
estimation is applied on an individual basis to          
bring the distribution of individuals in the sample          
into closer agreement with independent current          
estimates of the population according to age, sex          
and race characteristics ***( Armed forced          
personnel who are eligible to be interviewed are             
not included in the second-stage ratio estimate and          
receive a factor of 1)***.  This factor is defined           
for each person to adjust for the difference                 
between weighted counts of persons (using the above          
five weight components) and independent estimates            
of the number of persons, within the defined cells.          
These independent estimates are projections based            
on the 1990  Census population controls adjusted             
for the undercount.

For household crimes, the characteristics of the wife in a
husband-wife household and the characteristics of the head
of household in other types of households are used to
determine the ratio adjustment factors.  This procedure is
considered more precise than simply using the
characteristics of the head of household since sample
coverage is generally better for females than males.

For estimates involving incidents rather than
victimizations, further adjustments are made to those cases
where an incident involved more than one person.  These
incidents have more than one chance of being included in the
sample so each multiple-victimization is reduced by the
number of victims.  Thus, if two people are victimized
during the same incident, the weight assigned to that
incident is the person weight reduced by one-half so that
the incident cannot be counted twice.  However, the details
of the event's outcome as they related to the victim are
reflected in the survey results.  No adjustment is necessary
in estimating data on household crimes because each separate
crime is defined as involving only one household.

Series Victimizations

A series victimization is defined as six or more similar but
separate crimes which the victim is unable to recall
individually or describe in detail to an interviewer. These
series crimes have been excluded from the tables because the
victims were unable to provide details for each event.  Data
on series crimes are gathered by the calendar quarter(s) of
occurrence, making it possible to match the timeframes used
in tabulating the data for non-series crimes. (See Table
110).

The effect of combining series and non-series crimes,
counting each of the series crimes as a single victimization
based on the details of the most recent incident, was
included in the initial release of the 1980 data.***(See
Criminal Victimization in the United States; 1979-80
Changes, 1973-80 Trends, BJS Technical Report, NCJ-80838,
July 1982)***  The report showed that victimization counts
and rates were higher in 1979 and 1980 when the series
crimes were added.  However, rate changes between these 2
years were basically in the same direction and significantly
affected the same crimes as those affected when only non-
series crimes were analyzed.

Accuracy of Estimates

The accuracy of an estimate is a measure of its total error,
that is, the sum of all the errors affecting the estimate: 
sampling error as well as nonsampling error.                 
                                                
The sample used for the NCVS is one of a large number of
possible samples of equal size that could have been obtained
by using the same sample design and selection procedures. 
Estimates derived from different samples would differ from
one another due to sampling variability, or sampling error.

The standard error of a survey estimate is a measure of the
variation among that estimate from all possible samples. 
Therefore, it is a measure of the precision (reliability)
with which a particular estimate approximates the average
result of all possible samples.  The estimate and its
associated standard error may be used to construct a
confidence interval.  A confidence interval is a range of
numbers which has a specified probability that the average
of all possible samples, which is the 
true unknown value of interest in an unbiased design, is
contained within the interval.  About 68% of the time, the
survey estimate will differ from the true average by less
than one standard error.  Only 10% of the time will the
difference be more than 1.6 standard errors, and just 1 time 
in 100 will it be greater than 2.5 standard errors.  A 95%
confidence interval is the survey estimate plus or minus
twice the standard error, thus there is a 95% chance that
the result of a complete census would fall within the
confidence interval.

In addition to sampling error, the estimates in this report
are subject to nonsampling error.  While substantial care is
taken in the NCVS to reduce the sources of nonsampling error
throughout all the survey operations, by means of a quality
assurance program, quality controls, operational controls,
and error-correcting procedures, an unquantified amount of
nonsampling error remains still.

Major sources of nonsampling error are related to the
inability of the respondents to recall in detail the 
crimes which occurred during the 6 months prior to the
interview.  Research based on interviews of victims obtained
from police files indicates that assault is recalled with
the least accuracy of any crime measured by the NCVS.  This
may be related to the tendency of victims to not report
crimes committed by offenders who are not strangers,
especially if they are relatives.  In addition, among
certain groups, crimes which contain elements of assault
could be a part of everyday life, and are therefore
forgotten or not considered important enough to mention to a
survey interviewer.  These recall problems may result in an
understatement of the actual rate of assault. 

Another source of nonsampling error is the inability of some
respondents to recall the exact month a crime occurred, even
though it was placed in the correct reference period.  This
error source is partially offset by interviewing monthly and
using the estimation procedure described earlier.
Telescoping is another problem in which incidents that
occurred before the reference period are placed within the
period.  The effect of telescoping is minimized by using the
bounding procedure previously described.  The interviewer is
provided with a summary of the incidents reported in the
preceding interview and, if a similar incident is reported,
it can be determined whether or not it is a new one by
discussing it with the victim.  Events which occurred after
the reference period are set aside for inclusion with the
data from the following interview. 

Other sources of nonsampling error can result from other
types of response mistakes, including errors in reporting
incidents as crimes, misclassification of crimes, systematic
data errors introduced by the interviewer, errors made in
coding and processing the data.  Quality control and editing
procedures were used to minimize the number of errors made
by the respondents and the interviewers.

Since field representatives conducting the interviews
usually reside in the area in which they interview, 
the race and ethnicity of the field representatives
generally matches that of the local population.  Special
efforts are made to further match field representatives 
and the people they interview in areas where English is not
commonly spoken.  About 90% of all NCVS field
representatives are female.

Standard errors measure only those nonsampling errors
arising from transient factors affecting individual
responses completely at random (simple response variance);
they do not reveal any systematic biases in the data.  As
calculated in the NCVS, the standard errors would partially  
measure nonsampling error arising from some of the above
sources, such as transient memory errors, or accidental
errors in recording or coding answers, for example.


Computation and Application of Standard Errors

Deriving standard errors which are applicable to a wide
variety of items and which can be prepared at a moderate
cost requires a number of approximations. Therefore, three
generalized variance function (gvf) constant parameters
(identified as "a", "b", and "c" in the following section)
were developed for use in calculating standard errors.  The
parameters provide an indication of the order of magnitude
of the standard errors rather than the precise standard
error for any specific item.

Direct variances were calculated using the balanced 
repeated replication (BRR) method.  The estimates and 
their corresponding variances were fit to the standard
3-parameter model to obtain the value of the parameters.


NOTATION

x         =    the estimated number (level) of personal or   
             household victimizations or incidents

y         =    the base; either the total number of persons  
              or households (for victimization rates) or     
           the total of all victimizations
               (for incident characteristics)
 
p         =    the estimated proportion, resulting from      
               dividing the number of victimizations into    
               the base.  Also, the percentage or
               rate expressed in decimal form.  The          
               percentage is 100p and the rate per thousand  
               is 1000p.

s(p)      =    the estimated standard error of p

               It follows that:

                                                             
              s(percentage)  =  s(100p)   =  100 s(p)

                                                             
              s(rate)        =  s(1000p)  = 1000 s(p)

a,b,c     =    the generalized variance function parameters  
              (see chart)

1996 Parameter Set                       a          b      c
1. Overall Person Crime Estimates    -0.00004325  2096   1.683
2. Person Crime Domain Estimates     -0.00006543  2378   1.883
3. Overall Property Crime Estimates  -0.00009283  1567   1.332
4.Estimates Property Crime Domain    -0.00005524  2281   1.203

1997 Parameter Set                       a         b       c
1. Overall Person Crime Estimates      .00017479  2792   1.720
2. Person Crime Domain Estimates       .00016972  2945   2.010
3. Overall Property Crime Estimates    .00008155  1299   2.091
4. Property Crime Domain Estimates     .00023869  2278   1.731

1998 Parameter Set                        a          b      c
1. Overall Person Crime Estimates     -0.00007044  2029   3.320
2. Person Crime Domain Estimates       0.00001297  2656   3.390
3. Overall Property Crime Estimates   -0.00002708  1717   1.839
4. Property Crime Domain Estimates     0.00003528  2263   1.835

1999 Parameter Set                        a          b      c
1. Overall Person Crime Estimates     -0.00032791  2134   2.953
2. Person Crime Domain Estimates      -0.00026646  2579   2.826
3. Overall Property Crime Estimates   -0.00001550  1744   1.912
4. Property Crime Domain Estimates     0.00006087  2422   1.788


Parameter set #1 is used for the overall person crime
estimates (Table 1). These are the person crime estimates 
by crime category for the whole population, not
disaggregated by any victim, offender, or incident
characteristics, nor any variable related to reporting to
police.

Parameter set #2 is used for the person crime domain
estimates.  These are the person crime estimates
disaggregated by victim, offender, or incident
characteristics, or any variable related to reporting to
police.

Parameter set #3 is used for the property crime estimates
for the whole population (Table 1). These are the property
crime estimates by crime category for the whole population,
not disaggregated by any household characteristics, nor any
variable related to reporting to police.

Parameter set #4 is used for the property crime domain
estimates.  These are the property crime estimates
disaggregated by household characteristics, or
any variable related to reporting to police.

For the statistic from Table 1 that corresponds to the 
crime category "all crimes" (i.e., person and property
crimes together), parameter set #3 should be used.  When 
the person and property estimates are combined (i.e., all
crimes) and disaggregated by victim, household, incident
characteristics, as well as any variable related to
reporting to police, parameter set #4 should be used for 
the best estimate of the corresponding variance.  All 
of the following examples are based upon 1997 data.  These
formulas are applied in the same way for other years.

Formula 1.  Levels:  Standard errors for the estimated
number of victimizations or incidents may be calculated 
by using the following formula:  Standard error of 'x'
equals the square root of ('a' times 'x' plus 'c' times
'x' raised to the exponent 3 divided by 2)

The following example illustrates the proper use of 
Formula 1.  Table 1 in 1997 shows 606,660 completed 
robberies.  This estimate and the appropriate
parameters are substituted in the formula as follows:

The following example illustrates the proper use of Formula
1.  Table 1 shows 606,660 completed robberies in 1997; this
estimate and the appropriate parameters are substituted in
the formula as follows: Standard error of 606,660 robberies
equals the square root of (.00017479 times 606,660 squared
plus 2792 times 606,660 plus 1.72 times 606.660 raised to
the exponent 3 divided by 2). S(x)=50704

Formula 2. Proportions, Percentages, and Rates:  Standard
errors for the estimated victimization rates or percentages
are calculated using the following formula:  Standard error
of 'p' equals the square root of (('b' times percentage 'p'
times (1 minus the percentage p) divided by y) plus (('c'
times percentage 'p' times the square root of p minus p)
divided by the square root of y))

The following example demonstrates the use of Formula 2. 
Table 3 in 1997 shows an estimated robbery rate of 7.4 per
1,000 persons between the ages of 20 and 24, based on a
total of 17,648,850 persons in this age range. Substituting
the appropriate values into the formula yields:              
             
The standard error of 10.8 robberies per 1,000 persons age
20-24 equals the square root of ((2945 times .0074 times (1
minus .0074)) divided by.648850) plus ((2.010 times .0074)
times ((the square root of .0074) minus .0074) by the square
root of 17648850 of 648850)

=0.0012 or 1.2 per thousand

Thus, the 95% confidence interval is 7.4 per 1,000 plus 
or minus 2.4:  an interval of 5.0 to 9.8 per 1,000.

Formula 3.  Difference in rates or percentages with
different bases:  The standard error of a difference 
between two rates or percentages having different bases is
calculated using the formula: Standard error of the 
difference between percentage 1 and percentage 2 equals the
square root of the variance of percentage 1 plus the
variance of percentage 2 minus 2 times rho times the
standard deviation of percentage 1 times the standard 
deviation of percentage 2

where: rho is the year-to-year correlation between p1 and p2
(see chart); and var(p1) and var(p2) are the square of the
standard error of p using Formula 2 for each rate and
substituting:

           p1 = first percent or rate (expressed as a        
         proportion in decimal form)

           y1 = base from which first percent or rate was    
             derived 
           
         p2 = second percent or rate (expressed as a         
              proportion in decimal form)

         y2 = base from which second percent or rate was     
          derived


        Year-to-Year Correlation Between Estimates


Because of the year-to-year overlap in the sample, the same
households and persons contribute to annual estimates for
different years.  This year-to-year correlation between
estimates is measured by rho  In general:

         P   =   0 when estimates are for the same year

         rho     does not equal to 0 for year-to-year        
                 comparisons 

                 When comparing estimates that are 1 year    
                 apart, use rho as shown below.

                 When comparing estimates that are 2 years   
                 apart, multiply rho  by 1/2

                 When comparing estimates that are more than 
                 2 years apart, assume rho=0.


Following are NCVS year-to-year correlation values 
for major crime categories.
                                                             
                                                                
TYPE OF CRIME               1996-98       1997-98       1997-99        1998-99
                        CORRELATION   CORRELATION   CORRELATION    CORRELATION
-----------------------------------------------------------------------------
Total Crimes                 0.20          0.41         0.20           0.41
Total Personal Crimes        0.15          0.30         0.15           0.30
Crimes of Violence           0.15          0.31         0.15           0.31
Rape/Sexual Assault          0.02          0.04         0.02           0.04
Robbery                      0.02          0.04         0.02           0.04
Assault                      0.15          0.30         0.15           0.30
Purse Snatching/Pocket       0.01          0.03         0.01           0.03
Total Property Crimes        0.19          0.38         0.19           0.38
Burglary                     0.10          0.21         0.10           0.21
Motor Vehicle Theft          0.04          0.08         0.04           0.08
Theft                        0.17          0.34         0.17           0.34




If estimates are uncorrelated, rho = 0.  Hence, omitting the
term containing rho in the formula will provide an accurate
standard error for the difference between uncorrelated
estimates.  On the other hand, if the two estimates have a
strong positive correlation, omitting the last term will
cause overestimation of the true standard error.  If the
numbers have a strong negative correlation, this will cause
underestimation of the actual standard error. 

The following example illustrates the use of Formula 3. 
Table 4 in 1997 lists  victimization rate for aggravated
assault for males as 10.9 per 1,000 and the rate for 
females as 6.4 per 1,000.  The total number of males 
in the population is 106,598,660 and the total of females,
113,240,440.  Noting that rho = 0 because the two estimates
are for the same year and placing the appropriate values in
the formulas yields: Variance of percentage 1 equals ((2945
times .0109 times ( 1 minus .0109)) divided by 6598660)
plus (2010 times .0109 times (square root of .0109) minus
.0109) divided by the square root of 6598660 which
equals 0.000000496

Variance percentage 2 equals ((2945 times 0.0064 times (1
minus 0.0064)) divided by 113240440) plus ((2.010 times
.0064 times (the square root of 0.0064) minus 0.0064)
divided by the square root of 113240440 which 
equals 0.000000254

The 95% confidence interval around the difference of 4.5 per
thousand is approximately the difference plus or minus 1.7
per thousand (a difference between 2.8 and 6.2 per
thousand).

The ratio of a difference to the standard error of the
difference is the "z score", which is associated with a
given statistical level of significance.  For example, a
ratio with an absolute value of 2.0 (1.96, to be exact) or
greater indicates that the difference is significant at the
95% confidence level (or greater); a ratio with an absolute
value between 1.6 and 2.0 indicates the difference is
significant at a confidence level between 90% and 95%; a
ratio with an absolute value less than 1.6 denotes a
confidence level less than 90%.  In the previous example,
the ratio of the difference (.0045) to the standard error
(.00087) is 5.17.  Thus the aggravated assault rate for
males and females was significantly different at a
confidence level exceeding 95%.

Formula 4.  Differences in percentages of a single response
variable with the same base:  The standard error of the
difference between two percentages derived from a single
response variable with the same base is calculated
using the formula: The standard error of the difference
between two percentages derived from a single response
variable with the dame base is calculated using the formula:
Standard error of the difference between percentage 1 and
percentage 2 equals the square root of the (variance of
percentage 1 plus the variance of percentage 2 minus (2
times rho= times the standard deviation of percentage 1
times the standard deviation of percentage 2))

rho= equals negative square root of ((percentage 1 times
percentage 2) divided by ((1 minus percentage 1) times 1
minus percentage 2))

All other terms are as defined in Formula 3, except that y1
and y2 are the same common base, y.

The following example, which uses Table 43 for 1997, 
illustrates the use of Formula 4.  The proportion of
single-offender violent crime victimizations involving
relatives was 11.6% and the proportion involving
acquaintances (well-known or casual) was 42.7%, out of a
total of 7,287,440 single-offender violent crime
victimizations.  Substituting the appropriate values
into the formula gives: Variance of p1 equals (2945 times
.108 times ((1-.108) divided by 6737660) plus (2.010 times .
108 times (the square root of:  108) divided by the square
root of 6737600 equalling .000061 

Variance of p2 equals (2945 times .452 times (1-.452)
divided by 6737660 plus (2.010 times .452 times (the square
root of .452) minus .452) divided by the square root of
6737660 equalling .000185
                                                            
The confidence interval around the difference at one
standard error is from -32.6% to -36.2% (-34.4% plus or
minus 1.8%).  The ratio of the difference (-0.344) to its
standard error (0.018) is -19.11.  Since 19.11 is greater
than 2.0, the difference between these two percentages is
statistically significant at a confidence level exceeding
95%.

The standard error of the difference equals the square root
of .000061 plus .000185 + 2 times ( the square root of
.09987) times .008 times .01361 equalling 1.8 percent




Number of households and persons interviewed by year.                   
                 
                                     
Year   Number of     Household     Number of    Response
       households    response      persons      rate for
       interviewed   rate          interviewed  persons                
                                     
1996      43,390        93%          85,330         91%
                                     
1997      42,910        95%          79,470         90%
                                     
1998      43,000        95%          80,000         89%
                                     
1999      43,000        93%          77,750         89%

  



Criminal Victimization Glossary              


Age - The appropriate age category is determined by the
respondent's age on the last day of the month before the
interview. 

Annual household income - The total income of the household
head and all members of the household for the 12 months
preceding the interview. Includes wages, salaries, net
income from businesses or farms, pensions, interest,
dividends, rent, and any other form of monetary income. 

Aggravated assault - Attack or attempted attack with a
weapon, regardless of whether or not an injury occurred and
attack without a weapon when serious injury results. 

With injury - An attack without a weapon when serious injury
results or an attack with a weapon involving any injury.
Serious injury includes broken bones, lost teeth, internal
injuries, loss of consciousness, and any unspecified injury
requiring two or more days of hospitalization. 
Threatened with a weapon - Threat or attempted attack by an
offender armed with a gun, knife, or other object used as a
weapon, not resulting in victim injury. 

Assault - An unlawful physical attack or threat of attack.
Assaults may be classified as aggravated or simple. Rape,
attempted rape, and sexual assaults are excluded from this
category, as well as robbery and attempted robbery. The
severity of assaults ranges from minor threat to incidents
which are nearly fatal. 

Burglary ( also Household burglary) - Unlawful or forcible
entry or attempted entry of a residence. This crime usually,
but not always, involves theft. The illegal entry may be by
force, such as breaking a window or slashing a screen, or
may be without force by entering through an unlocked door or
an open window. As long as the person entering has no legal
right to be present in the structure a burglary has
occurred. Furthermore, the structure need not be the house
itself for a burglary to take place; illegal entry of a
garage, shed, or any other structure on the premises also
constitutes household burglary. If breaking and entering
occurs in a hotel or vacation residence, it is still
classified as a burglary for the household whose member or
members were staying there at the time the entry occurred. 

Completed burglary - A form of burglary in which a person
who has no legal right to be present in the structure
successfully gains entry to a residence, by use of force, or
without force.  

Forcible entry - A form of completed burglary in which force
is used to gain entry to a residence. Some examples include
breaking a window or slashing a screen. 
Unlawful entry without force - A form of completed burglary
committed by someone having no legal right to be on the
premises, even though no force is used. 
Attempted forcible entry - A form of burglary in which force
is used in an attempt to gain entry. 

Collection year - The set of victimizations reported to NCVS
in interviews conducted during the same calendar year. This
set may include victimizations which occurred in the
previous calendar year, due to the retrospective nature of
the NCVS interview. Collection year data are used in tables
beginning in 1996.   See "Data year."

Commercial crimes - Crimes against commercial establishments
of any type are not included in the survey. Commercial
establishments include stores, restaurants, businesses,
service stations, medical offices or hospitals, or other
similiar establishments. For victimizations occurring in
commercial establishments, the crime is included or not
included depending upon whether the survey respondent was
threatened or harmed in some way or personal property was
taken. 

Crime classification - Victimizations and incidents are
classified based upon detailed characteristics of the event
provided by the respondent. Neither victims nor interviewers
classify crimes at the time of interview. During data
processing, a computer program classifies each event into
one type of crime, based upon the entries on a number of
items on the survey questionnaire. This ensures that similar
events will be classified using a standard procedure. The
glossary definition for each crime indicates the major
characteristics required to be so classified. If an event
can be classified as more than one type of crime, a
hierarchy is used which classifies the crime according to
the most serious event that occurred. The hierarchy is:
rape, sexual assault, robbery, assault, burglary, motor
vehicle theft, theft. 

Data year - The set of victimizations reported to NCVS all
of which occurred within the same calendar year.  For all
years prior to 1996, NCVS data are based upon data year. 
Beginning in 1996 and later years, data are based upon
collection year.  See "Collection Year."

Ethnicity - A classification based on Hispanic culture and
origin, regardless of race. 

Head of household - A classification which defines one and
only one person in each housing unit as the head. Head of
household implies that the person rents or owns (or is in
the process of buying), the housing unit. The head of
household must be at least 18, unless all members of the
household are under 18, or the head is married to someone 18
or older. 

Hispanic - A person who describes himself as
Mexican-American, Chicano, Mexican, Mexicano, Puerto Rican,
Cuban, Central American, South American, or from some other
Spanish culture or origin, regardless of race. 

Household - A person or group of people meeting either of
the following criteria. (1) people whose usual place of
residence is the same housing unit, even if they are
temporarily absent. (2) people staying in a housing unit who
have no usual place of residence elsewhere. 

Household Burglary - See burglary

Incident - A specific criminal act involving one or more
victims and offenders. For example, if two people are robbed
at the same time and place, this is classified as two
robbery victimizations but only one robbery incident. 

Marital status - Every person is assigned to one of the
following classifications: (1) married, which includes
persons in common-law unions and those who are currently
living apart for reasons other than marital discord
(employment, military service, etc.); (2) separated or
divorced, which includes married persons who are legally
separated and those who are not living together because of
marital discord; (3) widowed; and (4) never married, which
includes persons whose marriages have been annulled and
those who are living together and not in a common-law union. 

Metropolitan area - See "Metropolitan Statistical Area." 

Metropolitan Statistical Area (MSA) - The Office of
Management and Budget (OMB) defines this as a population
nucleus of 50,000 or more, generally consisting of a city
and its immediate suburbs, along with adjacent communities
having a high degree of economic and social integration with
the nucleus. MSA's are designated by counties, the smallest
geographic units for which a wide range of statistical data
can be attained. However, in New England, MSA's are
designated by cities and towns since these subcounty units
are of great local significance and considerable data is
available for them. Currently, an area is defined as an MSA
if it meets one of two standards:  (1) a city has a
population of at least 50,000; (2) the Census Bureau defines
an urbanized area of at least 50,000 people with a total
metropolitan population of at least 100,000 (or 75,000 in
New England). The Census Bureau's definition of urbanized
areas, data on commuting to work, and the strength of the
economic and social ties between the surrounding counties
and the central city determine which counties not containing
a main city are included in an MSA. For New England, MSA's
are determined by a core area and related cities and towns,
not counties. A metropolitan statistical area may contain
more than one city of 50,000 and may cross State lines. 

Motor vehicle - An automobile, truck, motorcycle, or any
other motorized vehicle legally allowed on public roads and
highways. 

Motor vehicle theft - Stealing or unauthorized taking of a
motor vehicle, including attempted thefts. 

Completed motor vehicle theft - The successful taking of a
vehicle by an unauthorized person. 

Attempted motor vehicle theft - The unsuccessful attempt by
an unauthorized person to take a vehicle. 

Multiple offenders - Two or more persons inflicting some
direct harm to a victim. The victim-offender relationship is
determined by the offender with the closest relationship to
the victim. The following list ranks the different
relationships from closest to most distant: spouse,
ex-spouse, parent, child, other relative, nonrelative
well-known person, casual acquaintance, or stranger. (See
Nonstranger and Stranger.) 

Non-Hispanic - Persons who report their culture or origin as
something other than "Hispanic" as defined above. This
distinction is made regardless of race. 


Nonstranger - A classification of a crime victim's
relationship to the offender. An offender who is either
related to, well known to, or casually acquainted with the
victim is a nonstranger. For crimes with more than one
offender, if any of the offenders are nonstrangers, then the
group of offenders as a whole is classified as nonstranger.
This category only applies to crimes which involve contact
between the victim and the offender; the distinction is not
made for crimes of theft since victims of this offense
rarely see the offenders. 

Offender - The perpetrator of a crime; this term usually
applies to crimes involving contact between the victim and
the offender. 

Offense - A crime. When referring to personal crimes, the
term can be used to refer to both victimizations and
incidents. 

Personal crimes - Rape, sexual assault, personal robbery,
assault, purse snatching and pocket picking. This category
includes both attempted and completed crimes.  
Place of occurrence of crime - The location at which a crime
occurred, as specified by the victim. Survey measures of
crimes occurring in commercial establishments, restaurants,
nightclubs, public transportation and other similar places
include only those crimes involving NCVS measured crimes
against persons, not the establishments. Crimes against
commercial establishments and other places are not measured
by the survey. 

Property crimes - Property crimes including burglary, motor
vehicle theft, or theft. This category includes both
attempted and completed crimes. 

Purse snatching/Pocket picking - Theft or attempted theft of
property or cash directly from the victim by stealth,
without force or threat of force. 

Race - Racial categories for this survey are white, black,
and other. The "other" category is composed mainly of Asian
Pacific Islanders, and American Indian, Aleut, and Eskimo.
The race of the head of household is used in determining the
race of the household for computing household crime
demographics. 

Rape - Forced sexual intercourse including both
psychological coercion as well as physical force. Forced
sexual intercourse means vaginal, anal or oral penetration
by the offender(s). This category also includes incidents
where the penetration is from a foreign object such as a
bottle. Includes attempted rapes, male as well as female
victim and both heterosexual and homosexual rape. Attempted
rape includes verbal threats of rape. 

Rate of victimization - see "Victimization rate." 

Region - The States have been divided into four groups or
census regions: 

Midwest - Includes the 12 States of Illinois, Indiana, Iowa,
Kansas, Michigan, Minnesota, Missouri, Nebraska, North
Dakota, Ohio, South Dakota, and Wisconsin. 

Northeast - Includes the 9 states of Connecticut, Maine,
Massachusetts, New Hampshire, New Jersey, New York,
Pennsylvania, Rhode Island, and Vermont. 

South - Includes the District of Columbia and the 16 States
of Alabama, Arkansas, Delaware, Florida, Georgia, Kentucky,
Louisiana, Maryland, Mississippi, North Carolina, Oklahoma,
South Carolina, Tennessee, Texas, Virginia, and West
Virginia. 

West - Includes the 13 states of Alaska, Arizona,
California, Colorado, Hawaii, Idaho, Montana, Nevada, New
Mexico, Oregon, Utah, Washington, and Wyoming. 

Robbery - Completed or attempted theft, directly from a
person, of property or cash by force or threat of force,
with or without a weapon, and with or without injury.  

Completed/property taken - The successful taking of property
from a person by force or threat of force, with or without a
weapon, and with or without injury. 

Completed with injury - The successful taking of property
from a person, accompanied by an attack, either with or
without a weapon, resulting in injury. 

Completed without injury - The successful taking of property
from a person by force or the threat of force, either with
or without a weapon, but not resulting in injury. 

Attempted to take property - The attempt to take property
from a person by force or threat of force without success,
with or without a weapon, and with or without injury. 

Attempted without injury - The attempt to take property from
a person by force or the threat of force without success,
either with or without a weapon, but not resulting in
injury. 

Attempted with injury - The attempt to take property from a
person without success, accompanied by an attack, either
with or without a weapon, resulting in injury. 

Rural area - A place not located inside the Metropolitan
Statistical Area. This category includes a variety of
localities, ranging from sparsely populated rural areas to
cities with populations less than 50,000. 

Sample - The set of housing units selected by the U. S.
Census Bureau to be interviewed for the survey. All
occupants of the household age 12 or older are interviewed.
See methodology for sample inclusions and exclusions. 

Series - Six or more similar but separate events, which the
respondent is unable to describe separately in detail to an
interviewer. 

Sexual assault - A wide range of victimizations, separate
from rape or attempted rape. These crimes include attacks or
attempted attacks generally involving unwanted sexual
contact between victim and offender. Sexual assaults may or
may not involve force and include such things as grabbing or
fondling. Sexual assault also includes verbal threats. 

Simple assault - Attack without a weapon resulting either in
no injury, minor injury (for example, bruises, black eyes,
cuts, scratches or swelling) or in undetermined injury
requiring less than 2 days of hospitalization. Also includes
attempted assault without a weapon. 

With minor injury - An attack without a weapon resulting in
such injuries as bruises, black eyes, cuts or in
undetermined injury requiring less than 2 days of
hospitalization. 

Without injury - An attempted assault without a weapon not
resulting in injury. 

Stranger - A classification of the victim's relationship to
the offender for crimes involving direct contact between the
two. Incidents are classified as involving strangers if the
victim identifies the offender as a stranger, did not see or
recognize the offender, or knew the offender only by sight.
Crimes involving multiple offenders are classified as
involving nonstrangers if any of the offenders was a
nonstranger. Since victims of theft without contact rarely
see the offender, no distinction is made between strangers
and nonstrangers for this crime. 

Suburban areas - A county or counties containing a central
city, plus any contiguous counties that are linked socially
and economically to the central city. On data tables,
suburban areas are categorized as those portions of
metropolitan areas situated "outside central cities." 

Tenure - The NCVS recognizes two forms of household tenancy:
(1) owned, which includes dwellings that are mortgaged, and
(2) rented, which includes rent-free quarters belonging to a
party other than the occupants, and situations where rental
payments are in kind or services. 

Theft - Completed or attempted theft of property or cash
without personal contact. Incidents involving theft of
property from within the sample household would classify as
theft if the offender has a legal right to be in the house
(such as a maid, delivery person, or guest). If the offender
has no legal right to be in the house, the incident would
classify as a burglary. 

Completed - To successfully take without permission property
or cash without personal contact between the victim and
offender.  

Attempted - To unsuccessfully attempt to take property or
cash without personal contact. 

Urban areas - The largest city (or grouping of cities) in a
Metropolitan Statistical Area (see definition of
Metropolitan Statistical Area). 

Victim - The recipient of a criminal act, usually used in
relation to personal crimes, but also applicable to
households. 

Victimization - A crime as it affects one individual person
or household. For personal crimes, the number of
victimizations is equal to the number of victims involved.
The number of victimizations may be greater than the number
of incidents because more than one person may be victimized
during an incident. Each crime against a household is
assumed to involve a single victim, the affected household. 

Victimization rate - A measure of the occurrence of
victimizations among a specified population group. For
personal crimes, this is based on the number of
victimizations per 1,000 residents age 12 or older. For
household crimes, the victimization rates are calculated
using the number of incidents per 1,000 households.         
Victimize - To commit a crime against a person or household.
 
Violence, crimes of - Rape, sexual assault, personal robbery
or assault. This category includes both attempted and
completed crimes. It does not include purse snatching and
pocket picking. Murder is not measured by the NCVS because
of an inability to question the victim. 

Completed violence - The sum of all completed rapes, sexual
assaults, robberies, and assaults. See individual crime
types for definition of completed crimes. 

Attempted/threatened violence - The unsuccessful attempt of
rape, sexual assault, personal robbery or assault. Includes
attempted attacks or sexual assaults by means of verbal
threats. See individual crime types for definition of
attempted crimes 







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