The terrorist attacks of 11 September 2001 (9/11) in the USA
remain one of the sentinel global events of the decade, exerting
a profound influence on world affairs even 9 years later. Salib
was the first to label the drop in British suicide rates occurring
during the month of the attacks as a demonstration of
Durkheimian social principles.1
observed that temporary shifts in levels of social integration and
group cohesion induced by sentinel events could affect suicide
rates.2However, the influence of the attacks on these rates by site
has been inconsistent. Although rates dropped briefly throughout
England and Wales, both fatal and non-fatal rates rose in The
Netherlands in the months following 9/11.3In North America, a
post-attack, 24-month elevation in hospitalised non-fatal attempts
was observed in a single-site Michigan study,4whereas the rate of
suicide attempts treated in emergency departments across the
province of Ontario decreased for 3 days after the attacks. A more
complete analysis of post-attack suicide rates in the USA
represents an additional contribution to this international
discussion. We hypothesised that attack site effects would involve
a uniform, temporary decline in rates, and that these effects would
diminish progressively with increasing geographic distance from
the sites, and with increasing time after 11 September 2001.
A century ago, Durkheim
The unit of measure for this study was the daily mortality rate per
100000 people, and the study time frame included rates for the
180 days prior to and the 180 days after 9/11 (15 March 2001
to 10 March 2002). Access to official US mortality data files
was granted by the National Center for Health Statistics after
agency approval of the protocol. Injury-related mortality case
identificationutilisedtheWorld Health Organization’s
recommended Injury Classification criteria,5and non-injury event
case finding used standardised National Center for Health
Statistics definitions.6International Classification of Disease
(ICD) codes7used in this study were therefore as follows: suicides
(ICD–9: E950–E959; ICD–10: X60–X84, X87.0), deaths of
undetermined intent (ICD–9: E980–E989; ICD–10: Y10–Y34,
Y87.2, Y89.9), ill-defined cause deaths (ICD–9: CM 780–799.9;
ICD–10: R00–R99, excluding R95), pancreatic cancer (ICD–9:
CM 157; ICD–10: C25) and Alzheimer’s disease (ICD–9: CM
331; ICD–10: G30). The deaths of the 9/11 hijackers are designated
in the data-set as terrorism-related suicides (ICD–10: U03), and
the deaths of all those killed in the attacks as terrorism-related
homicides (ICD–10: U01 or U02),8and all of these deaths were
excluded from analyses. The deceased’s county of residence, rather
than county of death occurrence, was used as the geographic
locator for each case under the assumption that place of residence
would generally be more reflective of the sociocultural group with
which the deceased identified.
Except where primary metropolitan statistical areas included partial
county areas, sites were all constructed along county lines.
Standardised ‘immediate vicinity’ areas around the World
Trade Center and Pentagon attack sites were defined as the counties
within the New York City and the Washington–Arlington–
Alexandria,District of Columbia–Virginia–Maryland–West
Virginia (DC–VA–MD–WV) primary metropolitan statistical
areas respectively. The Pennsylvania crash site of Flight 93 was
in rural Somerset County.
Final 2001 US mortality figures suggested that annual,
nationwide rates for 2001 were not significantly influenced
by the terrorist attacks9and population-based surveys confirm
that post-attack manifestations of psychological distress were
Effect of 11 September 2001 terrorist attacks
in the USA on suicide in areas surrounding
the crash sites
Cynthia A. Claassen, Thomas Carmody, Sunita M. Stewart, Robert M. Bossarte, Gregory L. Larkin,
Wayne A. Woodward and Madhukar H. Trivedi
The terrorist attacks in the USA on 11 September 2001
affected suicide rates in two European countries, whereas
overall US rates remained stable. The effect on attack site
rates, however, has not been studied.
To examine post-attack suicide rates in areas surrounding
the three airline crash sites.
Daily mortality rates were modelled using time series
techniques. Where rate change was significant, both duration
and geographic scope were analysed.
Around the World Trade Center, post-attack 180-day rates
dropped significantly (t=2.4, P=0.0046), whereas comparison
condition rates remained stable. No change was observed
for Pentagon or Flight 93 crash sites.
The differential effect by site suggests that proximity may be
less important that other event characteristics. Both temporal
and geographic aspects of rate fluctuation after sentinel
events appear measurable and further analyses may
contribute valuable knowledge about how sociological forces
affect these rates.
Declaration of interest
The British Journal of Psychiatry (2010)
196, 359–364. doi: 10.1192/bjp.bp.109.071928
surprisingly attenuated outside of directly affected areas.10The
relationship between geographic distance and suicide rates was
therefore characterised in concentric circles (Fig. 1). All counties
falling outside the immediate vicinity but within a 150-mile radius
of an attack site were included in the first geographic tier around
the sites. Counties at a distance of more than 150 miles and less
than 300 miles from each site comprised the second tier. Counties
in the first geographic tier falling within more than one attack site
circle were eliminated from individual site analyses as were second
tier counties falling within the first tier for any site. Because of the
low daily count (not rate) of suicides around both the Flight 93
and Pentagon sites, we ultimately defined the ‘immediate vicinity’
of both sites to include all counties where any portion of the
county fell within a 150-mile radius of the attack site.
Given the limitations inherent in observational studies, mortality
rates could have fluctuated around 11 September 2001 for reasons
not directly associated with the sociological influence of the
attacks. Undetermined intent and ill-defined cause death rates
were examined because incomplete investigation protocols for
suicides often result in elevated numbers of ‘hidden’ suicides
within these mortality categories.10–13If local medical examiner’s
offices simply did not have the resources to investigate equivocal
deaths with the usual degree of care after the attacks because of
the increased mortality burden associated with the attacks,
numbers of deaths in these categories might have increased
significantly during this time period. Pancreatic cancer and
Alzheimer’s disease rates were also examined because these rates
were believed to be relatively unaffected by news of the attacks.
Finally, in order to identify seasonal or other recurrent spurious
effects on rates of suicide, we examined rates for equivalent
calendar days in the years 1998, 1999 and 2000. Pre-9/11 years,
rather than post-9/11 years, were used as controls, because the
anniversary effect so commonly seen after traumatic events might
have influenced suicide rate levels in subsequent years.
For all pre/post-9/11 comparisons, the day of 11 September 2001
was included in the pre-9/11 period. Pre- and post-9/11 mean
suicide rates were computed as the mean of a negative binomial
distribution because this method is appropriate for data based
on counts and allows estimation of a parameter to adjust for
overdispersion. A time series model of daily suicide rates was fit
with SAS Proc ARIMA (SAS version 9.1.3) for Windows using
only the pre-9/11 data so that a possible 9/11 effect would not
confound the model. The number of moving average and auto-
regressive components was determined by Akaike’s information
criteria (AIC) method.14For consistency of presentation, time
series analysis was used in all geographic areas even though
for the New York City 150- to 300-mile concentric circle,
District of Columbia 150-mile circle, and Somerset County
150-mile circle, the AIC method selected a model with no
moving average or autoregressive components (i.e. white noise).
The pre-9/11 model was then applied to the pre- and post-9/11
periods combined, and step functions with the step at 9/11 were
added to the model to test for a possible increase or decrease in
suicide rates due to the attacks–intervention analysis.15The step
functions are all zero when the 9/11 effect is hypothesised not to
be in operation and 1 when it is. To determine the length of time
when rates were affected by 9/11 events, models were fit with step
functions corresponding to possible durations of the 9/11 effect
from 30 days up to 180 days in intervals of 30 days. Step functions
are shown in Fig. 2. The step function that produced the best fit
was identified by the AIC goodness-of-fit statistic.16The same
modelling and testing strategy was used for suicide rates in the
control years (1998, 1999, 2000) and for control condition death
rates in 2001 (undetermined and ill-defined cause, pancreatic
cancer and Alzheimer’s disease). A P of 0.01 was used as a
cut-off for significance in all tests of effect in order to partially
compensate for spurious significant results, given the number of
New York City area analysis
Between 1990 and 2001, annual New York City primary metro-
politan statistical area suicide rates trended slightly downwards,
from a rate of 8.1/100000 (1990) to 5.6/100000 (2001), with
September suicide counts during those years averaging just over
8% (range 5.9–10.0) of all annual suicides. September 2001
suicides represented 6.98% of suicides for that year, ranking as
the second lowest September percentage occurring during those
Figure 3 shows the 2001 New York City primary metropolitan
statistical area daily rate of suicide for the 180 days before and
after 11 September 2001. The mean daily rates for the complete
pre- and post-attack periods were 0.017 and 0.014 suicides per
100000 people respectively. Using only the 181 day pre-9/11 data,
the AIC method showed an ARMA (0, 6) model best fit the data.
This model was refit, using all 361 days of data presented in Fig. 2.
The best-fitting model was produced by the step function in which
the effect lasted for 60 days after 9/11. Based on this model, the
Claassen et al
of impact of distance on suicide rates.
Illustration of concentric distance circles used in analysis
CT, Connecticut; DL, Delaware; MA, Massachusetts; MD, Maryland; ME, Maine;
NC, North Carolina; NH, New Hampshire; NJ, New Jersey; NY, New York state;
OH, Ohio; PA, Pennsylvania; RI, Rhode Island, SC, South Carolina; VA, Virginia;
VT, Vermont; WV, West Virginia.
Suicides after 9/11 terrorist attacks
daily suicide rate was estimated to be 0.016 per day per 100000
people when the 9/11 effect was absent, declining during this
60-day post-9/11 period by an estimated average of 70.0039
per day per 100000 people (horizontal line in Fig. 3). This decline
was significant (t=2.9, P=0.0035).
Figure 4 shows the mean, post-attack daily suicide rate broken
down into 30-dayincrements,
fluctuation over time. This included a second drop in rates,
between 151 and 180 days. As a result, the model in which the
9/11 effect lasted for the entire 180 days was also significant
(post-9/11 change in daily suicide rate of –0.0028 per 100000
people, t=2.4, P=0.0046), whereas models for 90, 120 and 150
days were not.
To determine whether post-9/11 declines in rates were similar
to those found in years prior to 2001, the analysis for 2001 was
repeated for each year from 1998 to 2000. No significant
post-9/11 effect was found for any duration of time for any of
these years. Although the mean change in 1998 over the post-9/
11 180-day period was numerically larger than the corresponding
mean change in 2001 (70.0034 v. 70.0028 respectively), it was
not significant at the 0.01 level. In total, these individual year
analyses revealed a statistically significant post-9/11 drop in daily
suicide rates only for the year 2001 (60 days: t=2.9, P=0.0035;
180 days: t=–2.8, P=0.0046), with differences estimated from
the time series model being very close to differences in observed
Finally, post-/pre-9/11 daily 2001 rate changes and significance
levels for control conditions were as follows: undetermined cause
of death (60 days: +0.0030, P=0.5207; 180 days: +0.00048,
P=0.4076), ill-defined cause of death (60 days: +0.0021,
P=0.2659, 180 days: +0.0034, P=0.0132), Alzheimer’s disease
(60 days: +0.00013, P=0.9318; 180 days: +0.00085, P=0.4535),
and pancreatic cancer deaths (60 days: –0.00019, P=0.9442; 180
days: +0.0033, P=0.0975). Thus, no post-9/11
significantly different at the 0.01 level from the corresponding
pre-9/11 rate for these conditions.
New York City 150-mile and 300-mile
concentric circle analyses
Mean suicide rates for pre-/post-attack time periods are also given
in Fig. 4 for the counties falling outside the New York City
primary metropolitan statistical areas but within a 150-mile radius
of the World Trade Center. The pattern of decreasing and
increasing rates over the 180-day post-9/11 period is generally
parallel to that found within New York City. Time series modelling
showed an ARMA (15,0) model resulted in the best fit of the
pre-9/11 data. This model detected a statistically significant
180-day post-9/11 estimated drop in suicide rates (70.0044,
t=72.6, P=0.0096) for counties within 150 miles of the attacks
– a difference that was again found to be very close to the observed
rate difference of 70.00447. Like the model for New York City,
the 60-day model trended downwards, but failed to reach
significance at a distance of 150 miles from the city. Neither
control year analyses nor other 2001 mortality categories revealed
significant post-9/11 rate changes, except that significant increases
in ill-defined cause daily death rates were observed for the 180-day
(+0.0052, t=3.4, P=0.0008), 150-day (P=0.0002), 120-day
(P=0.0054), and 90-day (P=0.0048) post-9/11 periods. This
pattern was also observed during control years and was therefore
interpreted as unrelated to the 9/11 attacks.
The concentric circle extending from 150 to 300 miles away
from Ground Zero demonstrated no significant difference in
suicide rates for any post-9/11 time period studied.
Pentagon area and Somerset County
The Washington DC primary metropolitan statistical areas
includes counties and portions of counties within the District of
Columbia, Virginia, West Virginia and Maryland. Suicide rates
within this area are generally somewhat higher than those found
in the New York City primary metropolitan statistical areas,
although raw suicide counts are about half the number found
there. Between 1990 and 2001, annual rates of suicide in the
District of Columbia ranged from a low of 6.6/100000 (1991) to
a high of 9.44/100000 (1994), without a clear trend over time
(12-year average: 7.95/100000). The suicide rate for 2001 was
7.44/100000, which was somewhat higher than the annual rate
for the previous 2 years. On average, September suicides
comprised 8.44% of annual District of Columbia suicides, whereas
the number of suicides occurring during September 2001
represented 8.0% of all suicides for that year.
Compared with pre-9/11 rates, no significant difference in
post-9/11 suicide rates was discernible for the Washington DC
primary metropolitan statistical areas or for the 150-mile circle
around the Pentagon. Although mean daily suicide rates dipped
slightly for the first 30 days after 9/11 in both areas (Fig. 3), they
then rose above pre-9/11 levels for the subsequent 2 months (e.g.
post-9/11 days 31–90). The same pattern was noted for the 150-mile
7180 7150 7120 790 760 7300 30 60 90120 150180
120, 150, and 180 day durations of post-9/11 effect.
Step functions indicating (from top down) 30, 60, 90,
daily suicide rates per 100000 people for 180 days before and
after 2001, September 11 and time series estimates of mean
New York City primary metropolitan statistical area
Claassen et al
circle around Somerset County. As a result, no pre-/post-9/11 rate
differences achieved significance and no control year or control
conditions were analysed.
Finally, there were also no significant post-9/11 rate trends in
the area within 150 miles of the Flight 93 crash site. The suicide
rate fluctuated above pre-9/11 rates on a monthly basis, but – like
the 150-mile circle around the Pentagon – the post-9/11 180-day
rate average around the Flight 93 crash site remained essentially
unchanged from the equivalent pre-9/11 rate.
This study examined trends in daily US suicide rates around the
crash sites after the 11 September 2001 terrorist attacks and found
that although the attacks did not significantly influence national
rates, the rates for individuals whose place of residence was within
150 miles of the World Trade Center were reduced. The effect was
most prominent during the first 2 months after the attacks, but
influenced average daily rates across a 180-day time period as well.
The effect was observable in an area extending 150 miles outwards
from Ground Zero, and the lack of post-9/11 rate change for other
cause-specific mortality conditions within this geographic area
suggests that the effect was not related to overburdened
death investigation and registration systems. The absence of a
corresponding effect in years preceding 2001 suggests that the
effect was also not because of seasonal rate fluctuations. The
notable absence of any such effect in the area surrounding both
the Pentagon and the Flight 93 crash sites contrasts sharply with
the World Trade Center pattern.
New York City and European response patterns
The decline in New York City suicide rates is perhaps not
surprising, given the profound impact of the event and its sequelae
on the daily lives of those who lived within the city. Countless
news reports from that time period document the increased social
cohesion among New York City residents, which included high
levels of support for Ground Zero clean-up workers and
uniformed civil servants.17,18This sociological response pattern
supports the Durkheimian position that increased group cohesion
precipitated the declining suicide rates.
Two alternative explanations seem less likely. The first is that
increased access to mental health treatment available in the city
via free, walk-in Project Liberty mental health clinics during the
months after the attacks mediated the drop in suicide rates.19–21
The second possibility is that, perhaps because of the media
attention, a temporary increase in tolerance for mental health
help-seeking may have occurred over the months following the
attacks independent of any increase in group cohesion, producing
an environment more supportive of treatment-seeking than usual.
Although either possibility may have contributed to the
maintenance of lower suicide rates over the latter part of the
180-day study time period, it is not likely that either would have
precipitated a significant drop in rates beginning immediately
after the attacks. Instead, it seems more likely that suicide rates
dropped on the morning of 12 September in direct response to
the event itself.
In the weeks and months following 9/11, the World Trade
Center attack was widely understood to be an attack on the
financial structure of first-world economies.22As two of the most
powerful economic centres in the world,23it is therefore perhaps
not so surprising that popular reaction and suicide rate
performance in New York City and Great Britain mirrored each
other. Within hours of the attacks British Prime Minister Tony
Blair declared that Britain stood ‘shoulder to shoulder’ with
America against the ‘new evil of mass terrorism’.24As a population
well acquainted with acts of terrorism, British people seem to have
responded in-kind during those initial post-attack days.
surrounding areas directly
Suicide rates per 100000 people for 2001 by time interval and geographic region.
Suicides after 9/11 terrorist attacks
The Dutch experience, however, may have been quite different.
Multiple sources since the attacks have suggested that 9/11 was
experienced as a divisive (rather than a unifying) social influence
in The Netherlands.25,26In short, a singular, global event seems to
have increased social cohesion in some societies, and to have
contributed to fragmentation of the social fabric in at least one
Negative Washington DC effect
In contrast to New York City and Great Britain, 9/11 apparently
did not have a significant influence on suicidal behaviour among
individuals whose place of residence fell within the District of
Columbia primary metropolitan statistical area, or within a
150-mile radius of the Pentagon. Other, post-attack population-
based surveillance reported normative rates of post-traumatic
stress disorder among Washington DC residents and higher rates
in more geographically distant cities, lending indirect corroboration
to this study’s findings in this area.10Why would the events of
9/11 have had less impact on residents of the US capital than on
residents of New York City? Differences in the shared experience
of the World Trade Center and Pentagon attacks afford one level
of explanation. The relative scope of the two attacks in terms of
death toll, impact on everyday life and news coverage all
contributed to an early designation of the World Trade Center site,
and not the Pentagon, as the symbolic ‘Ground Zero’.10In
addition, the 2001 anthrax attacks, which began on 18 September
2001, may have diverted attention within Washington DC, as the
final two letters were mailed to members of the US Senate. It
should be noted that Durkheim2also identified nineteenth
century political events with a seeming lack of effect and assumed
that the absence of an increase in collective loyalty to a ‘common
cause’ after these events was the primary reason for negligible rate
Relationship prior to 9/11 studies
This study’s positive findings stand in contrast to negative findings
from two other very recently published studies of post-9/11
New York City suicide rates.27,28As in this study, a drop in
suicides after 9/11 was noted in both reports, but the finding
was not regarded as significant in either. There are important
methodological differences across studies. In particular, although
both studies utilised a single, monthly data point (i.e. a monthly
count or rate of suicide) and examined longer post-attack time
periods, the present study adopted an increasingly common
approach in this line of investigation, involving time series analysis
of daily rates.29,30Given that demonstrations of post-crises suicide
rate fluctuations have uniformly been both nuanced and
transitory,30this more granular method may be necessary and
characterise the phenomenon.
Several methodological limitations must be kept in mind in
relation to this study’s findings. Our study locates fatalities by
residence of the deceased rather than by place of death, under
the assumption that the deceased’s cultural ties are better
described by place of residence, and this may influence findings
in places such as the Washington DC area with its highly
transitory population subgroups. Second, although daily rates of
suicide demonstrated relative consistency across years for a variety
of mortality conditions, suicide is a rare event and the relatively
small numbers of suicides near some attack sites may have
erroneously contributed to negative findings (type II error). In
particular, the rural nature of the Somerset crash site was
associated with exceedingly low suicide base rates, reducing both
the potential for a collective, shared 9/11 experience and the
capacity of our statistical approach to detect an effect. Finally, this
is a correlational study and the possibility therefore remains that
New York City effects were caused by some force other than the
events surrounding 9/11.
General factors contributing to effects
In the USA, the local World Trade Center effect spread outwards
to encompass an area with an approximate 300-mile diameter
(150-mile radius). England at its widest and longest is
approximately 300 miles by 460 miles. It is possible that the nature
or intensity of shared cultural response needed to affect factors
such as suicide rates may exist only within geographic areas of a
limited size and substantial population density. Regardless, the
contrasting nature of response across the New York City and
Washington DC primary metropolitan statistical areas, Great
Britain and The Netherlands suggest that event proximity may
be less important than other response characteristics. Based on
the 9/11 experience, contextual factors that may potentially
contribute to differential group response and suicide rate
fluctuation include: immediacy and intensity of shared threat
experience, leadership response, presence/absence of other threats
or serious concerns, and nature of local media coverage.
Over the past six decades, the annual US suicide rate has
varied by less than five people per 100000 – a time period in
the USAencompassing four
unprecedented advancement in the diagnosis and treatment of
mental illness. Considering the relatively intractable nature of
the rate during this time period a finding of even temporary
fluctuations within specific locations is noteworthy. Given that
both temporal and geographical aspects of suicide rates after
significant social events appear to be measurable, further research
of this kind may produce valuable insights into to how these rates
are mediated by sociological forces and which suicidal groups are
wars,seven recessions and
Cynthia A. Claassen, PhD, Clinical Research Core, VISN 2 Center of Excellence for
Suicide Prevention, and Associate Professor, Department of Psychiatry, University
of Rochester, New York; Thomas Carmody, PhD, Department of Clinical Sciences,
University of Texas Southwestern Medical Center, Dallas; Sunita M. Stewart, PhD,
Department of Psychiatry, University of Texas Southwestern Medical Center, Dallas;
Robert M. Bossarte, PhD, Epidemiology and Population Studies Core, VISN 2 Center
of Excellence for Suicide Prevention, and Assistant Professor, Department of
Psychiatry, University of Rochester, New York; Gregory L. Larkin, MD, MSPH,
FACEP, Department of Surgery (Emergency Medicine), Yale University, New Haven,
Connecticut; Wayne A. Woodward, PhD, Department of Statistical Science,
Southern Methodist University, Dallas, Texas; Madhukar H. Trivedi, MD, Department
of Psychiatry, University of Texas Southwestern Medical Center, Dallas, USA
Correspondence: Cynthia A. Claassen, PhD, c/o Center of Excellence,
Canandaigua VAMC, 400 Fort Hill Drive, Canandaigua, NY 14424, USA. Email:
First received 12 Aug 2009, final revision 21 Dec 2009, accepted 11 Jan 2010
C.A.C.’s work is partially supported by a grant from the American Foundation for Suicide
Prevention (AFSP) and the Timberlawn Foundation. R.M.B. and G.L.L.’s work was likewise
partially supported by AFSP.
The authors thank Chris Rogers, PhD, of the Research Data Center at the National Center
for Health Statistics, Hyattsville, Maryland, for his support during these analyses.
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10.1192/bjp.bp.109.071928 Access the most recent version at DOI: Download full-text
Wayne A. Woodward and Madhukar H. Trivedi
Cynthia A. Claassen, Thomas Carmody, Sunita M. Stewart, Robert M. Bossarte, Gregory L. Larkin,
suicide in areas surrounding the crash sites
Effect of 11 September 2001 terrorist attacks in the USA on
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