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. 2000;283(9):1205-1209 (doi:10.1001/jama.283.9.1205) JAMA
Andrés Villaveces; Peter Cummings; Victoria E. Espitia; et al.
in 2 Colombian Cities
Effect of a Ban on Carrying Firearms on Homicide Rates
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LETTER FROM COLOMBIA
Effect of a Ban on Carrying Firearms on
Homicide Rates in 2 Colombian Cities
Andre´s Villaveces, MD, MPH
Peter Cummings, MD, MPH
Victoria E. Espitia, MSc
Thomas D. Koepsell, MD, MPH
Barbara McKnight, PhD
Arthur L. Kellermann, MD, MPH
I
N LATIN AMERICA AND THE CARIB-
bean, an estimated 102 000 homi-
cides occurred in 1990 (46.0 per
100 000 person-years).
1
From 1983 to
1993, the annual rate of homicide in
Colombia increased 366%, from 24 to
88 per 100 000.
2
In contrast, the crude
homicide rate in the United States in
1993 was 9.5 per 100 000.
3,4
Two thirds
of all deaths of Colombian men aged 15
to 44 years were due to homicide in
1993.
5
Much of the recent increase in
fatal interpersonal violence in Colom-
bia has been concentrated in the coun-
try’s 3 largest cities, Bogota´, Medellı´n,
and Cali. These cities contain 23% of
the country’s population and account
for nearly 31% of its homicides.
6
In
1994, the rate of homicide in the city
of Cali was 124 per 100 000 person-
years
7
; in Bogota´, it was 68 per 100 000
person-years.
8
In 1993, firearms were involved in
80% of homicides in Colombia
5
com-
pared with 70% of homicides in the
United States in the same year.
9
Co-
lombian laws allow individuals to carry
firearms only after an individual per-
mit has been issued by the military
forces; the army has exclusive control
over firearm sales and issues gun per-
mits only to buyers who can offer a con-
vincing justification for ownership and
only after the buyer passes a back-
ground check for past illegal activity.
Individuals with a permit are allowed
to carry concealed firearms anywhere
and at any time, with the exception of
in government buildings and some pri-
vate buildings where posted. In prac-
tice, widespread smuggling has made
it difficult to enforce these laws.
10
In 1993, the mayor of Cali estab-
lished the Programa para el Desar-
rollo, la Seguridad y la Paz (Program for
Development, Security, and Peace),
known as DESEPAZ, in an effort to stem
the city’s rising rate of homicide.
11
Ob-
jectives of the program included the
strengthening of democratic institu-
tions, community empowerment, pri-
ority needs assessment, and a commu-
nication strategy for promotion of
peaceful conflict resolution.
7
To moni-
tor patterns and trends in homicide
Author Affiliations: Departments of Epidemiology (Drs
Villaveces, Cummings, and Koepsell), Health Ser-
vices (Dr Koepsell), and Biostatistics (Dr McKnight),
School of Public Health and Community Medicine, and
the Harborview Injury Prevention and Research Cen-
ter (Drs Villaveces, Cummings, and Koepsell), Univer-
sity of Washington, Seattle; Department of Interna-
tional Health, Rollins School of Public Health (Dr
Villaveces) and the Emory Center for Injury Control
(Dr Kellermann), Emory University, Atlanta, Ga; and
Programa DESEPAZ, Epidemiologı´a de la Violencia, Al-
caldı´a Municipal de Cali, Universidad del Valle, Cali,
Colombia (Ms Espitia).
Corresponding Author and Reprints: Andre´ s Vil-
laveces, MD, MPH, Harborview Injury Prevention and
Research Center, Box 359960, 325 Ninth Ave, Seattle,
WA 98104-2499 (e-mail: avillav@u.washington.edu).
Section Editor: Annette Flanagin, RN, MA, Manag-
ing Senior Editor.
For editorial comment see p 1193.
Context Homicide is a leading cause of death in Colombia, with much of the fatal
interpersonal violence concentrated in the country’s largest cities. Firearms are in-
volved in as much as 80% of homicides in Colombia.
Objective To evaluate the effect of an intermittent police-enforced ban on carrying
firearms on the incidence of homicide in urban Colombia.
Design Interrupted time-series study with multiple replications.
Setting Cali, Colombia, during 1993 and 1994 and Bogota´ , Colombia, from 1995
through August 1997.
Participants The populations of Cali and Bogota´.
Intervention Carrying of firearms was banned on weekends after paydays, on holi-
days, and on election days. Enforcement included establishment of police checkpoints
and searching of individuals during traffic stops and other routine law enforcement
activity.
Main Outcome Measure Homicide rates during intervention days were com-
pared with rates during similar days without the intervention; estimates were based
on comparisons within the same month, day of week, and time of day.
Results There were 4078 homicides in Cali during 1993 and 1994 (114.6 per 100 000
person-years). In Bogota´ , 9106 homicides occurred from 1995 through August 1997
(61 per 100 000 person-years). The incidence of homicide was lower during periods
when the firearm-carrying ban was in effect compared with other periods (multivariate-
adjusted rate ratio, 0.86 [95% confidence interval {CI}, 0.76-0.97] for Cali, and 0.87
[95% CI, 0.77-0.98] for Bogota´).
Conclusion An intermittent citywide ban on the carrying of firearms in 2 Colom-
bian cities was associated with a reduction in homicide rates for both cities.
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more closely, a fatal injury surveil-
lance system was established. A de-
tailed description of this system can be
found elsewhere.
2
These programs were
later copied in Bogota´ and a similar sur-
veillance system was created in 1995.
5
In an effort to reduce the incidence
of homicide, the mayors and the met-
ropolitan police commanders of both
cities decided to ban carrying firearms
on weekends after a payday, on holi-
days, and on election days. These pe-
riods are historically associated with
higher rates of homicide.
5,7
We sought to determine whether a
ban on carrying firearms was associ-
ated with any change in the incidence
of homicide.
METHODS
Study Sites and Periods
Cali (population, 1 803 662 in 1994) is
the third largest city in Colombia, and
Bogota´ (population, 5 639 328 in 1996)
is the largest city and the nation’s capi-
tal. Both are major cultural, indus-
trial, and agricultural centers.
In Cali, the study took place from the
beginning of 1993 through the end of
1994. In Bogota´, the study took place
from the beginning of 1995 through Au-
gust 1997. During these times, a spe-
cial injury surveillance system col-
lected data on all homicides. In addition,
all elements of the DESEPAZ program,
aside from the ban on carrying fire-
arms, were continuously in effect.
The Intervention
Intervention strategies were imple-
mented through a coordinated effort by
the metropolitan police and the may-
ors’ offices. By special decree, citizens
(including those with permits to carry
firearms) were forbidden to carry their
firearms during periods that were ex-
pected to have higher rates of homi-
cide, based on past experience. These
periods included weekends after semi-
monthly paydays, holidays, any week-
end that adjoined a holiday, and elec-
tion days. However, because of the effort
involved, the intervention was applied
to only some of the eligible periods. In
addition, it was applied to some
weekends that did not come after pay-
days or adjoin a holiday.
The public was notified about the ban
through the media. Television, news-
papers, and radio were used to dissemi-
nate this information and the pro-
grams reached national attention,
making it unlikely that individuals were
uninformed about its application times.
The ban made reference only to fire-
arms, not to other weapons. In some
cases, police confiscated knives or other
weapons because the presence of these
other weapons was thought to be dan-
gerous (eg, an individual who was in a
fight).
The intervention took effect at 6
PM
on the day before the designated pe-
riod began and ended at 6
AM on the
day after the last day of the period.
Thus, a typical weekend intervention
began at 6
PM on Friday and ended at
6
AM on the subsequent Monday. In
Cali, the intervention was applied on
34 occasions for a total of 89 days; the
intervention was first applied in No-
vember 1993 and was applied inter-
mittently during 1994. In Bogota´, the
intervention was applied on 22 occa-
sions for a total of 67 days during 3
intervals: December 1995 through
March 1996, December 1996 through
February 1997, and March and April
1997.
During intervention days, police es-
tablished checkpoints throughout the
city and, at their discretion, searched
individuals. Searches for weapons were
also conducted during traffic stops and
other law enforcement activities. Lo-
cations for checkpoints were selected
by each local police commander and
were usually in areas where police be-
lieved criminal activities were com-
mon. Police also searched individuals
by going into bars and clubs and search-
ing patrons. During the ban, police
policy directed that if a legally ac-
quired firearm was found on an indi-
vidual, the weapon was to be tempo-
rarily taken from the individual and the
individual fined. Individuals without
proof of legally acquiring the firearm
were to be arrested and the firearm per-
manently confiscated.
Study Data
A homicide was defined as any inten-
tional killing of 1 person by another,
regardless of method. The DESEPAZ
program in Cali and the program in
Bogota´ collected data on a weekly ba-
sis from the National Institute of Le-
gal Medicine and Forensic Sciences, the
metropolitan police, the district attor-
ney’s office, and the Department of
Transportation. A committee of repre-
sentatives from each of these organi-
zations met once per week to review
cases and share information. All of these
activities were coordinated by an epi-
demiologist.
The fatal injury surveillance system
collected information on victim iden-
tity, place and time of injury, and in-
jury circumstances. The manner of
death (suicide, homicide, or uninten-
tional) and the mechanism of death (eg,
fall, knife, firearm) were determined
from information obtained at the scene
from witnesses and from other infor-
mation provided by the police, transit
police, coroner, hospital, or postmor-
tem examination. In both cities, pa-
thologists of the National Institute of
Legal and Forensic Medicine per-
formed autopsies on all cases of injury-
related death. Data were entered only
after the final medical examiner’s di-
agnosis was obtained. All counts, rates,
and analyses are limited to homicides
of Cali and Bogota´ residents.
Data regarding the time of assault
were missing for 16 (0.4%) of the 4078
homicides in Cali; this proportion was
so small that we simply omitted these
records from analyses that required time
of assault. Data regarding time of as-
sault were missing for 1965 (21.6%) of
the 9106 homicides in Bogota´. We ini-
tially omitted these records from analy-
ses that required time of assault. We
then classified assaults by the age and
sex of the victim and whether the event
occurred on a payday weekend, other
weekend, or weekday; within each stra-
tum formed by these variables, we im-
puted missing values for hour of as-
sault using an approximate Bayesian
bootstrap method.
12
This imputation
process was carried out 10 times; all
LETTER FROM COLOMBIA
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at University Of North Carolina - Chapel Hill on July 12, 2010 www.jama.comDownloaded from
analyses of Bogota´ data that used im-
puted information were carried out on
each of the 10 imputed data sets and
all estimates, variances, and confi-
dence intervals (CIs) were calculated
using methods suitable for combining
data based on multiple imputa-
tions.
13,14
Analysis
The study design was that of an inter-
rupted time series with multiple repli-
cations; the intervention was applied in-
termittently in both cities, allowing us
to compare periods with the interven-
tion with similar periods without the
intervention.
Counts of deaths and total popula-
tion data were obtained from the Cali
and Bogota´ surveillance databases. The
number of homicides that occurred dur-
ing each hour were categorized by sex,
age (,15, 15-35, or .35 years), and
whether a firearm was used. Rates were
calculated on the basis of person-
years of exposure for Cali in 1993
(1 748 815) and 1994 (1 803 662) and
Bogota´ in 1995 (5 510 040), 1996
(5 639 328), and through the end of Au-
gust 1997 (3 831 624).
We first carried out a stratified analy-
sis using the method of indirect stan-
dardization. The stratification catego-
ries were weekday, payday weekend,
other weekend, time of year grouped
into 4-month intervals, and time of week
grouped into 28 equal intervals of 6
hours each. The stratum-specific rates
on nonintervention days were applied
to the person-time distribution of the in-
tervention days to obtain an expected to-
tal number of deaths.
15
The observed
number of deaths on intervention days
was then divided by this expected num-
ber to obtain a standardized mortality ra-
tio. Finally, a standardized rate for the
intervention group was calculated as the
product of its crude rate and the stan-
dardized mortality ratio.
To control for potential confound-
ing more completely, incidence rate ra-
tios were estimated using negative bi-
nomial regression to compare periods
with the intervention with all other pe-
riods, controlling for other character-
istics of periods that were potential con-
founders.
16,17
We divided each week into
28 consecutive 6-hour periods and in-
cluded 27 variables, coded 0 or 1, to ac-
count for variation in homicide inci-
dence among these intervals. Similarly,
we used 11 variables to account for
variation by month of the year. Addi-
tional variables were used to indicate
whether a weekend followed a payday
and whether a day was a holiday or elec-
tion day. To control for any trend in ho-
micide rates over the study period, the
days were assigned consecutive num-
bers. This continuous variable was in-
cluded in the models by using 2 frac-
tional polynomial terms as described by
Royston and Altman.
18,19
Categories of
age and sex were also examined as po-
tential confounders.
If a person was planning to assault
someone with a firearm, that person
might decide that it was too risky to carry
a firearm during an intervention period
and delay an assault for a few days to a
period not covered by the intervention.
If this occurred, any apparent reduc-
tion in homicide during intervention pe-
riods might be followed by a compen-
satory increase in homicides shortly after
the intervention. To examine this pos-
sibility, we created a variable for the 7-day
interval immediately following each in-
tervention period, coded 0 or 1, to see if
homicides were more common after the
intervention period.
Because the police intervention fo-
cused on finding and confiscating fire-
arms, we used the same regression
methods to estimate the effect of the in-
tervention on firearm-related and other
homicides. To test whether the asso-
ciation of the intervention with fire-
arm vs nonfirearm homicides was sig-
nificantly different, we repeated the
analysis using multinomial logistic re-
gression.
20
The populations of both cit-
ies during each 6-hour period were
treated as cohorts in which each indi-
vidual could experience 3 possible out-
comes: survival, death by firearm ho-
micide, or death by other homicide. The
same predictor variables were used.
Homicides might be serially corre-
lated over time. To check for any se-
rial correlation, we calculated autocor-
relation coefficients for the deviance
residuals of our final regression mod-
els using lags of 1 to 40 days.
16,21
RESULTS
During 1993 and 1994, there were 4078
homicides in Cali (rate, 114.6 per
100 000 person-years) (T
ABLE 1). There
were 9106 homicides in Bogota´ be-
tween 1995 and August 1997 (rate, 61
per 100 000 person-years) (Table 1). In
Cali, the incidence of homicide rose
from 104.9 per 100 000 person-years in
1993 to 124.3 per 100 000 person-
years in 1994, while in Bogota´, homi-
cides declined from 66.2 per 100 000
person-years in 1995 to 51.6 per
100 000 person-years in the first 8
months of 1997. Nearly two thirds of
the victims in both cities were men aged
15 to 34 years; for Cali, the homicide
rate in this group was 417.4 per 100 000
person-years; for Bogota´, it was 207.7
per 100 000 person-years. Seventy-
nine percent (n = 3235) of Cali homi-
cides involved firearms. Seventy-four
percent (n = 6735) of homicides in
Bogota´ were firearm-related. Most other
homicides involved a knife or other cut-
ting instrument.
In Cali, during nonintervention days
in 1993 and 1994, police confiscated
230 firearms (0.8 per day). During in-
tervention days, 307 guns were confis-
cated (4 per day).
22
Data on firearm con-
fiscation during intervention and
nonintervention days were not avail-
able for Bogota´.
Most of the Cali homicides (n = 3347)
occurred on days when there was
no intervention (107.5 per 100 000
person-years). For Bogota´, an average of
8262 homicides occurred during the
nonintervention periods (59.3 per
100 000 person-years). During days
when the intervention was in effect, there
were 715 homicides in Cali (161.8 per
100 000 person-years) and an average of
844 in Bogota´ (81 per 100 000 person-
years); as expected, the homicide rate was
higher during these weekend and holi-
day periods. We divided periods into 3
categories: weekdays, payday week-
ends, and other weekends. Within each
LETTER FROM COLOMBIA
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at University Of North Carolina - Chapel Hill on July 12, 2010 www.jama.comDownloaded from
of these 3 categories, standardized ho-
micide rates were lower when the inter-
vention was in effect for Cali (T
ABLE 2).
For Bogota´, we found similar results ex-
cept in the category of other weekends
(nonpayday), for which the rate was
slightly higher during intervention pe-
riods (Table 2).
After adjusting in a regression model
for weekend periods, holidays, pay-
days, 6-hour periods within each week,
month of year, and the overall trend in
homicide rates, the incidence of homi-
cide in Cali during periods when the
ban was in effect was significantly lower
than in nonintervention periods (rate
ratio, 0.86; 95% CI, 0.76-0.97). The rate
ratio for Bogota´ using only records with-
out missing data (7141 observations)
was 0.87 (95% CI, 0.76-0.99). The rate
ratio for Bogota´ using these data supple-
mented with observations derived from
10 imputed data sets to account for
missing data (9106 observations) was
0.87 (95% CI, 0.77-0.98).
Further adjustment for slight changes
in the age and sex distribution of the
population over time had no impor-
tant effect on these estimates. In the 7
days following intervention periods, the
incidence of homicide was not substan-
tially different from that during com-
parable nonintervention intervals (for
Cali, rate ratio, 1.03 [95% CI, 0.94-
1.13] for Bogota´, rate ratio, 0.99 [95%
CI, 0.90-1.08]). There was no statisti-
cally significant evidence of serial cor-
relation in our regression models.
Although the ban focused on fire-
arms, we conducted a statistical test of
the difference in the apparent effect of
the program on firearm-related and
other homicides; results were not sig-
nificant (P = .30 for Cali and P = .70 for
Bogota´). Furthermore, the direction of
association was inconsistent between
the 2 cities. In Cali, the intervention was
more strongly associated with nonfire-
arm homicides (rate ratio, 0.77 [95%
CI, 0.61-0.97]) than with firearm ho-
micides (rate ratio, 0.90 [95% CI,
0.79-1.03]). In Bogota´, however, the in-
tervention was more strongly associ-
ated with firearm-related homicides
(rate ratio, 0.85 [95% CI, 0.75-0.97])
Table 1. Numbers and Rates of Homicide by Year, Age, and Sex
Category
Cali, Colombia
Bogota´ , Colombia
No. of
Homicides
Homicide Rate per
100 000 Person-Years
No. of
Homicides
Homicide Rate per
100 000 Person-Years
Year
*
1993 1836 104.9 . . . . . .
1994 2242 124.3 . . . . . .
1995 . . . . . . 3645 66.2
1996 . . . . . . 3484 61.7
1997† . . . . . . 1977 51.6
Sex
Female 274 14.5 625 7.9
Male 3804 228.5 8481 119.8
Age, y
0-14 57 5.0 172 3.9
15-34 2825 196.1 6085 101.4
$35 1196 121.7 2849 63.0
Female, age, y
0-14 17 1.9 34 1.5
15-34 172 21.3 357 11.0
$35 85 16.2 234 9.6
Male, age, y
0-14 40 7.0 138 6.2
15-34 2653 417.4 5728 207.7
$35 1111 242.3 2615 126.0
*
Ellipses indicate not applicable.
†Data are through August 31, 1997.
Table 2. Numbers, Rates, and Standardized Mortality Ratios for Homicides During
Intervention and Nonintervention Periods
Period
No. of
Homicides
Crude Homicide
Rate per 100 000
Person-Years
Standardized
Homicide
Rate
*
Standardized
Mortality Ratio
(95% Confidence
Interval)
Cali, Colombia, 1993-1994
Intervention 715 161.8 89.0 0.83 (0.77-0.89)
Nonintervention 3347 107.5 107.5 Reference
Weekdays†
Intervention 26 87.6 79.5 0.94 (0.61-1.38)
Nonintervention 1908 84.6 84.6 Reference
Payday weekends
Intervention 468 162.1 139.1 0.82 (0.75-0.90)
Nonintervention 585 169.6 169.6 Reference
Nonpayday weekends
Intervention 221 178.8 141.7 0.86 (0.75-0.98)
Nonintervention 854 165.8 165.8 Reference
Bogota´ , Colombia, 1995-1997‡
Intervention 844.3 81.3 54.2 0.92 (0.86-0.97)
Nonintervention 8261.7 59.3 59.3 Reference
Weekdays†
Intervention 46 38.3 40.6 0.96 (0.70-1.28)
Nonintervention 4011.9 42.2 42.2 Reference
Payday weekends
Intervention 303.9 82.0 79.4 0.78 (0.70-0.87)
Nonintervention 1861.9 101.8 101.8 Reference
Nonpayday weekends
Intervention 494.4 90.2 93.4 1.02 (0.94-1.12)
Nonintervention 2387.9 91.4 91.4 Reference
*
Rates were standardized to the unexposed population using indirect standardization methods.
†Weekday intervention periods were holidays that did not fall on a weekend.
‡Numbers and rates for Bogota´ are based on data from 10 imputations of hour of death (1965 observations imputed).
LETTER FROM COLOMBIA
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at University Of North Carolina - Chapel Hill on July 12, 2010 www.jama.comDownloaded from
than with other homicides (rate ratio,
0.88 [95% CI, 0.72-1.06]).
COMMENT
During 1993 and 1994, an aggressive
program of banning and confiscating
firearms from residents was intermit-
tently applied in Cali. A similar pro-
gram was replicated in Bogota´ from
1995 through 1997. In Cali, we found
that the rate of homicide was 14% lower
(95% CI, 3%-24%) than expected dur-
ing periods when the ban on carrying
firearms was in effect. In Bogota´, the in-
cidence was 13% lower (95% CI, 1%-
24%) during intervention periods.
Whenever an exposure such as a law
or police activity is applied to an en-
tire population, the possibility exists
that any apparent effect on outcomes
could be due to other temporal changes
that were not accounted for in the
analysis. Our study, however, is un-
usual in that the intervention was ap-
plied intermittently. This provided an
opportunity to separate the interven-
tion effect from the overall change in
homicide rates. Whatever additional
factors might have affected homicide
rates in these cities during the study
intervals, it seems unlikely that they
would have reduced homicides selec-
tively during periods when the police
intervention was in effect.
Another study has suggested that
confiscation of illegally carried fire-
arms may reduce violent crime.
23
In
1994, a special unit of the Kansas City,
Mo, police department targeted illegal
gun carrying in a neighborhood with
high rates of firearm violence. During
the intervention period, firearm-
related crimes declined 49% in the in-
tervention neighborhood; no reduc-
tion was noted in a similar control
neighborhood that did not receive the
intervention. While the measured re-
duction in crime may have been due to
the intervention program, very few
weapons were seized.
In both Cali and Bogota´, the ban on
carrying firearms was applied to crimi-
nals and law-abiding citizens alike. Even
individuals who were normally autho-
rized to carry a firearm could not le-
gally do so on days when the decree was
in effect. Although a population-wide
approach of this sort may disarm more
law-abiding citizens than criminals, it
appears to have been associated with a
beneficial effect on homicide rates.
Although it appears that the interven-
tion in both cities prevented some ho-
micides, the mechanism for this ben-
efit is not clear. The program might have
prevented violence by incarcerating per-
sons who violated the firearms ban or
it might have deterred some people from
carrying a concealed weapon or even ap-
pearing in public during the interven-
tion. Although the program was specifi-
cally directed at firearms, we found that
the effect was not confined to firearm-
related homicides. This suggests that the
program may have worked in part by
promoting a visible and aggressive po-
lice presence, which discouraged or in-
terrupted episodes of serious interper-
sonal violence.
A program of this type may not have
a similar effect in cities where homi-
cide is less common. Furthermore, con-
stitutional restrictions on police search
procedures would prevent transferring
the methods used in Cali and Bogota´to
any city in the United States. Our study
suggests that police programs such as
those applied in Cali and Bogota´ can sup-
press serious interpersonal violence and
save lives. This kind of program may be
suitable for regions of the world where
homicide rates are very high and pro-
grams of this type are permissible.
Funding/Support: This study was supported in part
by an education grant from the Japan–Inter-
American Development Bank Scholarship Program and
a grant from the Instituto Colombiano para el Desar-
rollo de la Ciencia y la Tecnologı´a Francisco Jose´de
Caldas “Colciencias.” The data sets used for this analy-
sis were provided by the DESEPAZ Program Office of
Epidemiology of Violence from the Office of the Mayor
of Cali, the National Institute of Legal Medicine and
Forensic Sciences, and the Office of the Mayor of San-
tafe´ de Bogota´.
Acknowledgment: We are indebted to Rodrigo Guer-
rero, MD, DrPH, mayor of Cali from 1992-1994. We
also thank Gloria Sua´ rez, MD, National Institute of Le-
gal Medicine and Forensic Sciences, and Hugo Acero
Vela´ zquez, security advisor for Bogota´ during 1996-
1997, both of whom provided most of the informa-
tion from Bogota´ ; as well as Phillip L. Graitcer, DMD,
MPH, Stanley O. Foster, MD, MPH, and Lisa A. De-
Roo, MPH, who provided helpful comments on early
drafts of the manuscript.
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