Technical Assessment of Zhao and Thurman's 2001 Evaluation of the Effects of COPS Grants on Crime

Published by the Government Accountability Office on 2003-06-12.

Below is a raw (and likely hideous) rendition of the original report. (PDF)

United States General Accounting Office
Washington, DC 20548

          June 13, 2003

          The Honorable F. James Sensenbrenner
          Committee on the Judiciary
          House of Representatives

          Subject: Technical Assessment of Zhao and Thurman's 2001 Evaluation of the
          Effects of COPS Grants on Crime

          Dear Mr. Chairman:

          Community Oriented Policing Services (COPS) is a federal public safety program
          whose goals are to add officer positions to the streets of communities nationwide and
          to promote community policing. Since the program’s inception in 1994, local law
          enforcement agencies have received billions of dollars in grants to hire additional
          officers, acquire technology and civilian personnel, and implement innovative crime-
          prevention programs. To receive COPS grants, agencies are expected to implement or
          enhance community policing strategies illustrating community partnerships, problem
          solving, and organizational commitment. Given the large expenditures of funds, it is
          important for policy makers, among others, to have sound information on the
          effectiveness of the COPS program in reducing crime. You asked us to review one
          evaluation of the effectiveness of the COPS program—by Zhao and Thurman —and to
          render an assessment of its quality. In this report, we provide information on the
          extent to which this particular study’s conclusions are supported by the data the
          researchers used and the analyses they conducted. GAO statisticians and
          methodology specialists reviewed the study using standard and widely accepted
          statistical and social science research principles.

          Our assessment of Zhao and Thurman’s work cannot be construed to be an
          assessment of the COPS program itself. Since we have not reviewed the quality of any
          other COPS evaluation or conducted an independent evaluation of the program, we
          have no basis to judge whether or not the program has been effective in achieving its
          stated goals. It is also important to note that these types of aggregate level analyses
          that are intended to assess program effectiveness are extremely difficult to execute
          successfully, in part, because direct measures of important variables are not always

           Zhao, J. and Thurman, Q. A National Evaluation of the Effect of COPS Grants on Crime from 1994
          to 1999 (Dec. 2001).

          Page 1                                                                GAO-03-867R COPS Evaluation
We conducted our review of Zhao and Thurman’s study during a 3-week period in
May 2003. In addition to reviewing Zhao and Thurman’s December 2001 report, we
reviewed a November 2002 journal article by Zhao, Scheider, and Thurman based on
the same study,2 reviewed a May 2003 draft of an updated COPS study by the same
authors, and discussed data and statistical issues with these researchers in a
telephone call on May 27. In this report, we focus the majority of our comments on
Zhao et al.’s earlier COPS study (reported in December 2001 and November 2002). We
discuss differences between the earlier study and the May 2003 follow-up study in a
section at the end of this report. For ease of presentation, we refer to their original
work as the “2001 study.”


The Public Safety Partnership and Community Policing Act of 19943 authorized $8.8
billion in grants to be awarded to law enforcement agencies for fiscal years 1995 to
2000. Focused on crime-prevention, the act required, among other things, that half the
grants go to law enforcement agencies serving populations of 150,000 or less. The act
also required that grantees not supplant state and local funding, but rather use the
federal funds for additional law enforcement beyond what would have been available
without a grant. The Attorney General created the Office of Community Oriented
Policing Services to administer the grant programs and advance community policing
across the country.

The COPS office is tasked with promoting community policing through a variety of
types of grants, including:

•   Hiring grants, which are used to fund the hiring of additional police officers.
    Through its Universal Hiring Program, the COPS program provides funding
    directly to local, state, and tribal jurisdictions. The funding provides up to 75
    percent of the salaries and benefits for new officers for 3 years up to a maximum
    of $75,000 per officer. According to the COPS Office, 71,192 officers were funded
    and 63,592 officers were hired through hiring grants as of July 26, 2002. The COPS
    Office estimated that hiring grant awards totaled about $5.6 billion as of June 3,

•   Making Officer Redeployment Effective (MORE) grants, which are used to fund
    up to 75 percent of the total cost of acquiring new technologies and equipment
    and the hiring of civilians for 1 year. These are intended to allow police to spend
    more time patrolling the streets instead of on administrative and support tasks.
    According to the COPS Office, 24,436 full-time equivalent staff were redeployed
    through MORE grants as of July 26, 2002. The COPS Office estimated that MORE
    grant awards totaled about $1.3 billion as of June 3, 2003.

•   Innovative grants, which are used to promote innovative approaches to solving
    crime in specific areas such as domestic violence and drug abuse. The COPS

  Zhao, J., Scheider, C. and Thurman, Q. Funding Community Policing to Reduce Crime: Have COPS
Grants Made a Difference? Journal of Criminology & Public Policy, Nov. 2002 (vol. 2, no. 1).
  P.L. 103-322.

Page 2                                                             GAO-03-867R COPS Evaluation
    Office estimated that innovative grant awards totaled $820 million as of June 3,

Results in Brief

Our review of the 2001 study on the effects of COPS grants on crime rates indicated
that the results of their study should be viewed as inconclusive. We believe that the
study’s limitations in data and methods are significant and preclude meaningful
interpretation of the results. We cannot agree with Zhao et al. that their 2001 study
shows that some COPS grants (hiring and innovative) significantly reduced crime
because, among other things, important variables were omitted from their analyses,
the analytic models were misspecified, and the sample of cities included in the study
was limited. Further, we have concerns about the use of outdated census data for
control variables. Aside from concerns about data and methods, we question whether
the statistically significant crime reductions that Zhao et al. found are significant in a
practical sense.

While we cannot agree with the Zhao et al.’s conclusions, we also cannot say that
COPS grants are ineffective in reducing crime. A program’s effects and researchers’
ability to design studies that will accurately measure those effects are two different
things. Other studies, which we have not reviewed, may have taken a more rigorous
approach to assessing the effects of COPS grants on crime. We believe that a more
rigorous study would incorporate, among other things, more reliable, valid, and
complete measures; a more complete and generalizable sample of cities; and well-
specified analytic models.

In written comments on a draft of this report, the Department of Justice’s COPS
Office and Zhao and Thurman generally disagreed with our findings. The comments
reflected the view that our standards for critiquing Zhao et al.’s work were too
stringent, that we were incorrect in concluding that their statistical models were
misspecified, and that the statistical controls incorporated into their analytic models
were sufficient to account for the types of missing data we identified as limitations of
the study. In our response, we address why we continue to believe that these
limitations render the findings of this particular study inconclusive.

Summary of Analysis and Results of the 2001 Study

The 2001 study presented a statistical analysis of the effects of three types of grants—
hiring, MORE, and innovation—on the reported rates of violent and property crimes
over a 5-year period across 6,100 U.S. cities that received COPS grants. The analysis,
which looked separately at cities with populations greater than 10,000 and those with
populations less than 10,000, sought to determine how the reported crime rates
varied as a function of the amount of COPS funds received.

The variables used in the 2001 study are presented in table 1, along with the averages
and standard deviations for these variables across all cities included in the analysis.

Page 3                                                        GAO-03-867R COPS Evaluation
Table 1: Averages Across All Cities from 1994 to 1999

                                                                          Average      Standard deviation
Dependent variables (1995-1999)
Violent crime rate (per 100,000 population)                                 769.63                   674.50
Property crime rate (per 100,000 population)                              5,016.39                 2,820.74
Independent variables (1994–1998)
Hiring grants (per resident)                                                 $2.38                     3.72
Innovative grants (per resident)                                             $0.42                     2.45
MORE grants (per resident)                                                   $0.65                     1.45
Demographic control variables
% unemployment (1994-1998)                                                     4.97                    2.17
% minority (1990 census)                                                     30.40                    23.32
% single parent households (1990 census)                                     10.59                     4.09
% young people ages 15-24 (1990 census)                                      15.43                     4.59
% home owners (1990 census)                                                  56.92                    14.62
% people in same household for 5 or more years (1990 census)                 50.66                    10.03
Note: Zhao et al. used weighted averages to estimate the means of COPS grants and control variables.
Source: Zhao et al., December 2001 and November 2002.

Zhao et al. found that hiring grants significantly reduced reported violent and
property crimes in larger cities, but significantly increased those rates in smaller
cities. They speculated that the addition of police officers in smaller cities could
produce an increase in reported crime because, among other things, the increased
interaction between police and the community can help residents feel more
comfortable and willing to report crimes. Innovative grants also significantly reduced
the reported violent and property crime rates in larger cities, but had no significant
effect in smaller cities. MORE grants had no discernable effect in larger cities, or on
reported violent crimes in smaller cities, but they significantly increased the rates of
reported property crimes in the smaller cities. Zhao et al. concluded that innovative
programs, which are targeted at specific crime problems or jurisdictions, had the
strongest effect on reducing reported crime rates. They also observed that “crime
reduction in the United States is not a unitary phenomenon” in light of the different
effects found in large versus smaller cities.

Our Review Indicated Several Problems with the 2001 Study

Our review revealed several problems with the 2001 study that cast doubt on the
validity of the conclusions about the effectiveness of COPS grants. The problems we
identified pertain to Zhao et al.’s interpretation of their findings, omission of
important variables from the analysis, misspecifications in the analytic models used,
and sample selection issues. We also had some concerns about the outdated nature of
census data used as control variables in the 2001 study.

The Meaning of the Study’s Findings Can Be Interpreted Differently

The finding that COPS grants exerted different effects on crime patterns in large
versus small cities led the researchers to observe that crime reduction is not a unitary
phenomenon. While this may be the case, one can also conclude that the study’s
findings are equivocal, inconsistent, and inconclusive.

Further, while the crime-reducing effects that Zhao et al. found for hiring and
innovative grants may have been statistically significant, they could also be

Page 4                                                                    GAO-03-867R COPS Evaluation
characterized as quite small in a practical sense.4 Table 2 demonstrates this point by
presenting a summary of Zhao et al.’s estimates.

Table 2: Estimates of the Effects of Three Types of COPS Grants, from Zhao et al. (2001)

City                     Crime                     Hiring          Innovative             MORE
type                     type                     Grants                 grants           grants
>10,000                  Violent                     -5.26*             -12.93*            -0.11
                         Property                 -21.63*               -45.53*            -1.52
1,000 - 10,000           Violent                      0.83*                1.06             2.48
                         Property                     8.97*               11.98           31.20*
All cities 1000+         Violent                      -1.86             -12.26*             0.28
                         Property                   -10.44              -43.85*            -0.28
Note: An asterisk (*) denotes that the estimated effect was statistically significant.
Source: GAO summary of Zhao et al. 2001 data.

The coefficients in table 2 indicate how much each grant dollar spent per person in
each city affected the rates of reported violent and property crimes; in other words,
how much of a change in the reported violent and property crime rates we might
expect if funding were increased by one dollar per resident. As shown in table 1, the
average annual COPS innovative grant across all cities amounted to $0.42 per person,
and the average rates of reported violent and property crimes, respectively, were
about 770 and 5,016 per 100,000. These coefficients imply that if COPS funding in
larger cities for innovative grants were doubled (from $0.42 to $0.84 per person), we
would expect the violent crime rate to go down by 0.7 of 1 percent (from 770 to 765
per 100,000).5 We would expect the reported property crime rate to go down by 0.4 of
1 percent (from 5,016 to 4,997 per 100,000).6 As small as the effects are, there are
reasons to question whether they accurately represent the expected returns on such
an investment, and these reasons are listed below in general order of importance.

Important Variables Were Omitted from the Analysis

While dummy variables were used in the 2001 study to control for unmeasured
differences across counties, the only city-level variables in the analysis that were
measured and explicitly controlled in the models of estimated COPS grant effects
were (1) the 1994 crime rate and (2) the six demographic variables shown in table 1.
Most conspicuously absent from these models is a measure of expenditures on police
that were not derived from COPS grants. The researchers told us they did not include

  Statistical significance means that the observed effect does not result from chance alone. The number
of observations in a sample can be an important determinant of statistical significance, with larger
sample sizes frequently being associated with statistically significant findings. Zhao et al.’s 2001 study
consisted of 36,605 observations, making it possible that statistically significant effects could have
been found even when they were small on a practical level.
  This is calculated as follows: From table 2, we see that in cities larger than 10,000, each dollar of
innovative grant funding was associated with a decrease of 12.93 violent crimes. $0.42 is 42 percent of
1 dollar, and 42 percent of 12.93 crimes equals 5.4. This represents the decrease in the expected crime
rate as innovative grant funding increased by $0.42 per person. If the violent crime rate were 770 per
100,000 population, doubling the $0.42 innovative grant expenditure per person would reduce the
violent crime rate by 5, or to about 765 per 100,000 population.
  The mean offered in Zhao and Thurman is a weighted average for all cities and only approximates the
mean for large cities. Because of that, and the severe skew in the distribution of average grant amounts
across cities (note the standard deviations in table 1), this may not be a very accurate way to estimate
the effect size. The skew in the distribution of grant amounts also suggests that it might have been
preferable to transform (using logarithms) those amounts prior to the analyses.

Page 5                                                                            GAO-03-867R COPS Evaluation
non-COPS funded police expenditures because such data are not available. Because
the COPS program supports only a portion of police agency budgets, however, we
believe the absence of any control for state and local expenditure to be a serious

Police departments that received COPS grants may have also received grants from
other programs (such as Byrne grants). These amounts could be correlated with
COPS funding amounts. For example, if a department is proficient in getting COPS
funding, it may be proficient in getting other funding, as well. Without separating
COPS funding from other types of funding that police agencies receive, we cannot be
sure how much of an effect COPS grants by themselves have on crime reduction.

The study also lacked any measure of city size beyond the dichotomy (i.e., population
smaller or larger than 10,000) used to split the sample of cities prior to model
estimation. Other omitted measures include such socioeconomic variables as per
capita income and percent male. County dummy variables controlled for some of the
problems associated with omitted variables, but they would not control effectively
for variables that differed across cities within counties, or variables that changed
within counties over time. For example, if state and local expenditures on police
varied across cities in a given county, using dummy variables to represent counties
would not take these differences or changes into account in estimating the
independent effect of COPS grants.

Misspecifications in the Analytic Models

The models employed in Zhao et al.’s analyses are two-factor fixed effects models
that employ 2,674 dummy variables representing the counties and 5 dummy variables
representing the years included in the analysis. These dummy variables controlled for
unmeasured variability across counties and over time, and they supplemented the
controls for prior rate of crime and the 6 demographic variables described above.
These models and the estimation procedures they involve are fairly sophisticated, but
since the data on crime rates and COPS funds were measured at the city level, we
believe that unmeasured variability would have been more effectively controlled had
dummy variables been used to distinguish cities, instead of the counties in which the
cities were located.7 With dummy variables representing counties, any unmeasured
and systematic variability across cities within the same county remained
uncontrolled and a potential source of bias in the parameters representing the effects
of the COPS grants estimated in the models.

Sample Selection Limited

Zhao et al.’s analysis is focused only on COPS program grants used to fund local city
police departments. Their report indicates that other law enforcement agencies, such
as state and county police agencies; sheriffs’ offices; campus police; and special
purpose law enforcement agencies such as court, forest, and park police, among
others, were excluded from their study. Since these other agencies accounted for

 A footnote in the 2001 study indicates that the researchers conducted initial analyses using city dummy
variables. However, they ultimately decided to use county dummy variables, and all the report findings
are derived from statistical models that included county rather than city dummy variables.

Page 6                                                                   GAO-03-867R COPS Evaluation
4,891 (or 40 percent) of the 12,070 law enforcement agencies receiving COPS grant
awards from 1994 to 1998, Zhao et al.’s study omitted a large portion of COPS grant
recipients. Further, there is likely to be considerable overlap across jurisdictions
receiving COPS grants (cities within counties, campus police within city

According to Zhao et al., the sample of cities included in their study represented a
subset of 6,100 of the 7,179 cities whose local city police departments received COPS
grants at some point during the period from 1994 to 1998.9 The researchers deleted
535 cities with populations less than 1,000, and 544 cities that lacked Uniform Crime
Reports (UCR) data.10,11 Four states (Delaware, Illinois, Kansas, and Montana)
contributed only 8 cities between them owing to missing UCR data. These omissions
may have affected the study’s results. Of greater concern, however, is the omission
of the potentially large number of cities that received no COPS funding at all. We
believe that cities with no COPS funding should have been included in the analyses in
order avoid sample selection problems and ensure that the results were generalizable
across all cities.

Concerns about Measures of Demographic Variables.

While the rates of violent crimes and property crimes were measured and allowed to
vary in each of the 5 years from 1994 to 1998, in the 2001 study at least 5 of the 6
demographic variables were derived from the 1990 census and fixed at their 1990
levels. We believe the 1990 figures would be a poor basis for estimates because in
many cities, the demographic characteristics of residents in 1990 would be expected
to be quite different from those in the mid- to late-1990s; and in all cities, these time-
invariant estimates would fail to account for the significant demographic changes

   For example, if the city of College Park, MD, received a COPS grant and the University of Maryland
campus police (located in College Park) received a separate COPS grant, their joint impact on the
city’s crime rates would not be included in this analysis.
   In the analysis, the crime rates from 1995 to 1999 were intentionally lagged a year to allow these
agencies to receive and deploy these funds.
    UCR is a nationwide database of police statistics consisting of crime data voluntarily reported to the
Federal Bureau of Investigation by nearly 17,000 city, county, and state law enforcement agencies.
UCR data form the basis for a Crime Index, which is used to gauge fluctuations in the nation’s overall
volume and rate of crime. The offenses included in the "violent crime" category are murder and
nonnegligent manslaughter, forcible rape, robbery, and aggravated assault. The offenses included in
the "property crime" category are burglary, larceny-theft, and motor vehicle theft, and arson.
    In personal discussions with the researchers, we learned that their 2001 published study contained
an error related to missing data. Specifically, the researchers had intended to eliminate cities from
their analysis if crime data were missing for even a single month of the year. However, the dataset they
obtained did not uniformly distinguish between missing data and "zero" reported crimes. In those
cases, the analysis would have produced an underestimate of the 12-month crime rate. After publishing
their results, the researchers corrected these data errors and reanalyzed the dataset. They told us that
the revised results did not differ substantially from those published. Time limitations prevented us
from assessing the revised results.
   In a November 2002 publication in the Journal of Criminology and Public Policy, Zhao et al.
explained that their analyses omitted cities without COPS grants because of concern that including
these cities would produce a downward bias in their estimation of COPS program effects. They said
this is because crime was decreasing across the board between 1994 and 1998 in cities with and
without COPS grants. We disagree with their rationale. Since Zhao and Thurman controlled for the
baseline rate of crime by including the 1994 rate in their model as a control variable, cities with COPS
grants would presumably have a higher rate of decrease than cities without COPS grants. We continue
to believe that Zhao and Thurman’s estimates of COPS program effects were biased as a result of
omitting cities that did not receive COPS grants.

Page 7                                                                  GAO-03-867R COPS Evaluation
that may have occurred over time. It was not entirely clear to us how the
unemployment data derived from the U.S. Department of Labor Statistics for the
years 1994 to 1998 were used in these models. However, it too represented a
potentially poor measure of unemployment in many cities. This is because data are
not available for cities with populations less than 25,000, and county-level rates were
used for those cities instead.

Comments on Zhao et al.’s Draft Updated COPS Study

Our previous comments pertain to the unpublished 2001 study by Zhao and Thurman
and the 2002 publication by Zhao, Scheider, and Thurman which resulted from the
study and which was virtually identical to the unpublished study in terms of the
primary results that were reported. That study, as we noted previously, relied on data
from 6,100 cities for which COPS grant data for the years 1994 to 1998, and UCR
crime data for the years 1994 to 1999, could be obtained. After reviewing that work,
we received a draft updated report from those authors that re-estimated the effects of
COPS grants on crime rates using data from an additional year (e.g., COPS grant data
for 1994-1999 and UCR data for 1994-2000) and models that incorporated updated
2000 census data and allowed the demographic characteristics to vary over time.
While these newer estimates, like those in the 2001 and 2002 reports, were derived
from models that used county dummy variables, we also received from the
researchers additional information that showed how results compared when they
used dummy variables representing cities in place of the county dummy variables.

These updated results are shown in table 3, along with the results from the
researchers’ prior study. The researchers have asserted, both in the draft updated
report and in their conversations with us, that these updated results are largely
consistent with the previously published results, and in a general sense we agree with
this. That is, with or without the newer data, regardless whether demographic factors
are allowed to vary, and regardless whether county or city or dummy variables are
used, both studies found (1) no evidence that COPS grants have diminished the crime
rates in cities with populations less than 10,000, and (2) some evidence that they have
done so in larger cities. Apart from this general observation, however, the results of
the two studies are inconsistent in that the size and significance of some of the
estimated effects of COPS grants differed under alternative specifications. For
example, when updated data and the time varying covariates were used, the
estimated effects of innovative grants on violent and property crimes in large cities
declined in size to less than half of the prior estimates, while the effects of MORE
grants increased more than 10-fold, and became statistically significant in the case of
property crimes.

  One difference in the crime rates analyzed in the two studies was that arson was included as a
property crime in the newer study, but not in the 2001 study.
   The authors provided us with additional information from their follow-up study on the analytic
results obtained when they used dummy variables to represent cities instead of counties. They found
that in large cities, the estimated effects of hiring grants on violent crimes doubled, the estimated
effects of MORE grants doubled and became statistically significant, and the effect of innovative grants
became statistically not significant. The effect of MORE grants on property crimes remained
significant in large cities when city dummy variables were used, but diminished to half the size that
was estimated by a model that used county dummy variables.

Page 8                                                                 GAO-03-867R COPS Evaluation
Since these newer results have not been finalized, it is premature for us to make a
final determination of their validity and usefulness. The researchers are to be
commended for the considerable effort they made to determine how reliable and
robust the estimated effects of the different COPS grants were over time, and under
alternative specifications. Nonetheless, the newer study that we reviewed had some
of the same limitations as the 2001 study. Specifically, the newer study (1) omitted
important variables, including measures of expenditures on police apart from COPS
grants, (2) omitted a large number of cities that did not receive COPS grants, and (3)
did not control for the effect of city size on crime in a more refined fashion than
dichotomizing city populations. Our review of the results of the newer analyses has
not fundamentally altered our view that the estimated effects of COPS grants on
reported violent and property crimes were small in a practical sense. Again, it is
important to note that this does not imply that COPS grants do not have positive
effects in reducing crime; only that it is hard to reach firm conclusions about their
effects from the particular studies we reviewed. Our technical assessment of Zhao et
al.’s work is not a commentary on the effectiveness of the COPS program.

Table 3: Zhao et al.’s Estimates of the Effects of Three Types of COPS Grants with Dummy Variables
Representing Counties in (a) 2001 Study Using 1994-1999 Data and (b) Draft Updated Study Using 1995-
2000 Data

  City                   Crime                COPS study                   Hiring        Innovative       MORE
  type                   type                                              grants            grants       grants
  >10,000                Violent              2001 study                    -5.26*          -12.93*        -0.11
                                          Draft updated study               -5.49*            -5.31*       -2.00

                         Property             2001 study                  -21.63*           -45.53*         -1.52
                                          Draft updated study             -25.22*           -20.65*       -21.47*

  1,000 - 10,000         Violent              2001 study                     0.83*             1.06             2.48
                                          Draft updated study                1.47*             0.60             2.92

                         Property             2001 study                     8.97*            11.98        31.20*
                                         Draft updated study                 7.91*             1.30        30.51*
Note: An asterisk (*) denotes that the estimated effect was statistically significant.
Source: GAO summary of Zhao et al.’s 2001 and updated studies.

Agency Comments and Our Evaluation

The Acting Deputy Director of the COPS Office and Professors Zhao and Thurman
provided us with written comments on a draft of this report. Their comments
contained a number of points that disagreed with the limitations we identified in our
assessment. The comments reflected the view that we (1) applied an overly stringent
standard to the study’s design and failed to consider the fact that this study was
better and more comprehensive than previous research on the subject; (2) were
incorrect in concluding that their statistical models were misspecified and did not
control for the effect of missing police expenditure data; (3) were ill-advised in
stating that including data on cities’ access to grants other than COPS grants would
have improved the estimates of COPS grant effects; (4) were ill-advised in stating that
including data on such socioeconomic variables as percentage of the population that
is male would have improved the estimates of COPS grant effects; (5) were incorrect
in stating that including data on COPS-funded jurisdictions within cities, such as

Page 9                                                                            GAO-03-867R COPS Evaluation
university police, would have improved the estimates of COPS grant effects; and (6)
were ill-advised in stating that including police departments in cities that did not
receive COPS funding would have improved the estimates of COPS grant effects. We
continue to disagree with the researchers on these key points and discuss our
reasons below.

First, with respect to the assertion that our standards were too high and that we did
not consider the advances made by this study, we would reiterate that the purpose of
our assessment was to determine the extent to which the conclusions of this
particular COPS study were supported by the data used and analyses conducted.
Because we were asked to review this single study and did not have time to review
any others, we cannot comment on whether and how this study’s approach to
evaluating the effectiveness of the COPS program may have been an incremental
improvement over other similar efforts. We acknowledge in the introduction to this
report that it is extremely difficult to assess program effectiveness via aggregate level
analyses. We also believe that the researchers should be commended for their efforts,
which involved merging data on more than 6,000 towns and cities over a multi-year
period from four different sources and using sophisticated methods to analyze those
data under a variety of specifications. But, in our estimation, the problems that we
identified with the research make the results more suggestive than conclusive.

Second, with respect to the assertion that the statistical models were both correctly
specified and sufficiently controlled for the effect of missing data on police
expenditures, we do not believe this was the case. Zhao et al. believe that we are
unjustifiably critical of their having used county rather than city dummy variables in
estimating the effects of COPS grants on crime rates. They point out that they ran
both their 2001 and 2003 analyses using both city and county dummy variables, and
the results of the two types of analyses did not differ substantially. While the
models incorporating county or city dummy variables do, as the authors assert,
explain a sizable portion (between 64 percent and 86 percent) of the variation in
reported crime rates across cities over time, this is not surprising and is largely
attributable to the very large number of dummy variables included in their models.
The proportion of variance explained, however, does not necessarily imply that the
estimates of the effects of COPS grants were unbiased. The authors, in our opinion,
are mistaken in their claim that the use of dummy variables controls for the effects of
all unmeasured differences between cities and over time. That is, the county dummy
variables do not control for unmeasured differences between cities within counties,
and even the combination of city and year dummy variables do not control for
differences within cities over time, unless the changes in all cities are similar. Crime
rates in cities did not show similar changes over time, however, and there are many

   The researchers noted that they recently collected original police expenditure data from 55 of the
largest police departments and found that including these data in the statistical models showed that
they had virtually no effect on their estimates of the effects of COPS funding. We appreciate the
difficulty of obtaining police expenditure data for large cities and endorse efforts to marshal
supporting evidence from a sample of those cities. However, we have not seen the results of these
analyses and have no basis to judge how representative these 55 cities are of large cities in general, or
whether the estimated effects of COPS grants from the 55 cities are generalizable to larger cities
   Bureau of Justice Statistics data on 62 local police departments serving cities with a population of
250,000 or more revealed a high degree of change in violent and property crime rates within the same
city over time. For example, New York’s reported violent crime rate dropped by 57 percent between

Page 10                                                                  GAO-03-867R COPS Evaluation
factors that can change in cities from one year to the next in ways that might affect
crime rates. For example, fluctuations in local, state, and other expenditures on
police could produce changes in crime rates within cities over time, and the failure to
control for such factors can seriously bias the estimates of the effects of COPS

Third, with respect to the assertion that omitting data on cities’ access to grants other
than COPS grants probably did not affect the results, we are not convinced. We agree
that data on grants that cities receive are not readily available. However, we believe
that information on at least major grant programs could be obtained from the Office
of Justice Programs. To the extent that cities that receive COPS grants may be more
likely to receive other types of grants, omitting consideration of other grants that are
also targeted at reducing crime may lead to an overestimation of the effects of COPS
grants. By restricting their attention to COPS grants awarded to city and local police,
the researchers investigated the effects of only a portion of all COPS grants. They
ignored the effects of other grants and of state and local expenditures, generally, and
therefore increased the potential for obtaining biased estimates of COPS grant

Fourth, with respect to the assertion that the study’s results were not impaired by the
omission of such socioeconomic variables as percentage of the city population that is
male, we disagree with the researchers that this is not problematic. They assert that
(1) the dummy variables in their statistical models controlled for the effects of
socioeconomic variables other than those in their analyses, (2) a city’s male
population should not significantly affect the estimated effects of COPS grants on
crime, (3) the socioeconomic variables included in the analyses were sufficient and
grounded in widely accepted social disorganization theory, and (4) problems of
multicollinearity could have arisen had they included additional socioeconomic
variables. As with police expenditures, we maintain that data on factors affecting
crime rates that vary across cities and over time should be included in analyses, and
may not be sufficiently controlled by statistical models that use dummy variables to
control for unmeasured differences. While we do not know whether and how COPS
grant amounts to cities may be associated with the socioeconomic characteristics of
city residents, the literature indicating a gender difference in crime is extensive. To
the extent that socioeconomic characteristics affect crime rates, and to the extent
that cities that received COPS grants may have different socioeconomic
characteristics, we believe it would be wise to incorporate such variables into models
to lessen any potential bias in the estimates of the COPS grants on crime. Since this
study was intended to be an evaluation of the effects of COPS grants on crime and

1990 and 2000, while Nashville’s rate increased by 29 percent during that same time period. Similarly,
New York’s reported property crime rate dropped by 60 percent, while Nashville’s rate increased by 22
percent. (Police Departments in Large Cities, 1990-2000. Department of Justice, Bureau of Justice
Statistics, May 2002).
   Multicollinearity means that the independent variables are highly correlated. If this occurs, it is
impossible to distinguish between them in estimating their effects on the dependent variable.
   For example, a Bureau of Justice Statistics study indicated that men comprised 93 of the state prison
population in 2001; 93 percent of the federal prison population in 1997; and 90 percent of the local jail
population in 1996 (http://www.ojp.usdoj.gov/bjs/crimoff.htm#findings). Another study reported that
in 1960, 1975, and 1990, men were arrested at much higher rates than women for all crime categories
except prostitution (Steffenmeier, D. and Allen, E., “Gender and Crime: Toward a Gendered Theory of
Female Offending,” Annual Review of Sociology, 1996, vol. 22, pp. 459-87).

Page 11                                                                 GAO-03-867R COPS Evaluation
not as a test of social disorganization theory, we do not believe that limiting the
socioeconomic control variables to those dictated by this particular theory was
warranted. Finally, with 36,000 observations in their study, we do not believe that
multicollinearity would have been a problem had additional socioeconomic variables
been included in the analyses.

Fifth, with respect to the assertion that including data on COPS-funded agencies
within cities would not have improved the estimates of COPS grant effects, we
continue to believe that this cannot be known. Zhao and Thurman state that there is
no meaningful way to include such agencies—for example, park and university
police—in their statistical models because the jurisdictions overlap. They note that it
was neither necessary nor possible to estimate the effects of such agencies on crime
rates because they report crime incident data to the Federal Bureau of Investigation
separately and because census data for them are not readily available. We maintain
that by restricting their attention to crimes reported to local and city police
departments, the researchers are investigating the effect of only a portion of all COPS
grants and are looking at only a subset of all crimes reported. Again, we do not know
whether these restrictions result in an overestimate or underestimate of the effect of
COPS grants on crimes, but they can potentially bias their estimates. We
acknowledge that data may not be readily available for such an analysis, but that does
not mean they cannot be collected or that they are unimportant.

Sixth, with respect to the assertion that including data on police departments in non-
COPS funded cities would not have improved the estimates of COPS grant effects, we
continue to disagree. Zhao and Thurman note that because small cities are more
likely than large cities to not receive COPS funding, including nonfunded agencies in
their analysis could bias the findings towards showing an effect of COPS grants. It is
our view that missing cases, except when they are missing at random, should be
regarded as problematic. The 6,100 agencies that Zhao et al. analyzed represented
about 85 percent of the COPS-funded city and local police departments, 51 percent of
the total number of COPS-funded agencies, and 36 percent of the agencies that
participate in the UCR system. Some of these exclusions may have been unavoidable,
but their cumulative impact is likely to be non-negligible.

We do not know how or to what extent the findings that Zhao et al. obtained would
change if the limitations that we identified in our assessment were successfully
resolved. We do know, however, that while Zhao et al. may have performed the most
sophisticated and advanced research on the topic, drawing inferences or making
policy decisions about COPS grant effects from this work are unwarranted at this
time. Indeed, Zhao and Thurman are themselves continuing this work, an indication
that they also believe refinements are needed.

The comments from the COPS office and the researchers are reproduced in the
enclosure to this report. The COPS Office also provided us with technical comments,
which we incorporated in the report as appropriate.

                                        -- -- -- -- -- --

As agreed with your office, unless you publicly announce the contents of this report
earlier, we plan no further distribution of it until 30 days from the date of this report.

Page 12                                                       GAO-03-867R COPS Evaluation
We will then send copies of the report to the Attorney General and will make copies
available to others upon request. In addition, the report will be available at no charge
on GAO’s web site at http://www.gao.gov.

If you have any questions about this report, please contact me at (202) 512-8777. The
key contributors to this report were David Alexander, Carl Barden, Evi Rezmovic,
and Douglas Sloane.

Sincerely yours,

Laurie E. Ekstrand
Director, Homeland Security
 and Justice Issues

Nancy Kingsbury
Managing Director, Applied Research
 and Methods Issues

Enclosures - 2

Page 13                                                      GAO-03-867R COPS Evaluation
              Enclosure I
Enclosure I

 Page 14                    GAO-03-867R COPS Evaluation
          Enclosure I

Page 15                 GAO-03-867R COPS Evaluation
          Enclosure I

Page 16                 GAO-03-867R COPS Evaluation
               Enclosure II
Enclosure II

 Page 17                      GAO-03-867R COPS Evaluation
          Enclosure II

Page 18                  GAO-03-867R COPS Evaluation
          Enclosure II

Page 19                  GAO-03-867R COPS Evaluation
          Enclosure II

Page 20                  GAO-03-867R COPS Evaluation
          Enclosure II

Page 21                  GAO-03-867R COPS Evaluation
          Enclosure II

Page 22                  GAO-03-867R COPS Evaluation
                     Enclosure II


Page 23                             GAO-03-867R COPS Evaluation