and Marine Biology & Fisheries, Miller School of Medicine
and Rosenstiel School of Marine and Atmospheric Sciences,
Clinical Research Building, 10th Floor (R669), 1120 NW
14th St, Miami, FL 33136 (e-mail: firstname.lastname@example.org.
This brief was accepted March 27, 2008.
L. Vidal originated the study and led the writing of this
article with support from L.E. Fleming. W. LeBlanc
managed the data and performed statistical analyses. All
authors helped conceptualize ideas, interpret findings,
and provide critical review of the article.
This study was funded in part through the National
Institute of Occupational Safety and Health (grant R01
Human Participant Protection
This study was approved by the University of Miami’s
Miller School of Medicine institutional review board.
1. American Cancer Society. Cancer Facts and Figures
2007. Atlanta, GA: American Cancer Society; 2007.
Cancer Society guidelines for the early detection of
cancer. CA Cancer J Clin. 2000;50:34–49.
Smith RA, Mettlin CJ, Davis KJ, Eyre H. American
Society guidelines for the early detection of cancer, 2005.
CA Cancer J Clin. 2005;55:31–44.
Smith RA, Cokkinides V, Eyre HJ. American Cancer
Clinical Preventive Services. Washington, DC: Agency for
Healthcare Research and Quality; 2006. Available at:
Accessed May 19, 2008.
US Preventive Services Task Force. The Guide to
www.healthypeople.gov. Accessed August 8, 2008.
Healthy People 2010. Available at: http://
class matters: socioeconomic disadvantage, race/
ethnicity, gender, and smoking in NHIS 2000. Am J
Public Health. 2004;94:269–278.
Barbeau EM, Krieger N, Soobader MJ. Working
LeBlanc W, Pitman T. Obesity in US workers: the
National Health Interview Survey, 1986 to 2002. Am J
Public Health. 2005;95:1614–1622.
Caban AJ, Lee DJ, Fleming LE, Gomez-Marin O,
Agenda (NORA). Cross-sector research in the second
decade. Presented at the 2006 NORA Symposium;
Washington, DC; April 2006. Available at: http://www.
Accessed May 19, 2008.
Sorerholm SC. National Occupational Research
Documentation, National Health Interview Survey, 2000
(machine-readable data file and documentation). Hyatts-
ville, MD: National Center for Health Statistics; 2002.
National Center for Health Statistics. Data File
10. SAS Institute. Survey Data Analysis. Available at:
Accessed May 19, 2008.
11. Jabine JB. Reporting Chronic Conditions With NHIS.
Hyattsville, MD: National Center for Health Statistics,
12. Behrens V, Seligman P, Cameron L, Mathias CG,
Fine L. The prevalence of back pain, hand discomfort,
and dermatitis in the US working population. Am J Public
13. Health and Human Services, Centers for Disease
Control and Prevention. Health Risks in the United States
Behavioral Risk Factor Surveillance System at a Glance,
2007. Available at: http://www.cdc.gov/nccdphp/
publications/aag/pdf/brfss.pdf. Accessed May 19, 2008.
14. Carrie `re P, Baade P, Newman B, Aitken J, Janda M.
Cancer screening in Queensland men. Med J Aust.
15. Levy BT, Nordin T, Sinift S, Rosenbaum M, James
PA. Why hasn’t this patient been screened for colon
cancer? J Am Board Fam Med. 2007;20:458–468.
16. Miller DP Jr, Brownlee CD, McCoy TP, Pignone MP.
The effect of health literacy on knowledge and receipt of
colorectal cancer screening: a survey study. BMC Fam
17. Bagai A, Parsons K, Malone B, Fantino J, Paszat L,
Rabeneck L. Workplace colorectal cancer screening
awareness programs: an adjunct to primary care practice?
J Community Health. 2007;32:157–167.
18. Sorensen G, Barbeau EM. Integrating occupational
for research and practice. Med Lav. 2006;97:240–257.
Joe Murphy, MA
I applied the capture–recapture
method to estimate the World Trade
Center tower population at the time
of the September 11, 2001, terrorist
8965 survivors and 2152 confirmed
casualties. The capture–recapture
model suggested that an additional
4435 survivors were present, putting
15897). An accurate estimate repre-
sents the potential number at risk
for trauma as a result of direct expo-
sure to the events of the day. (Am J
Public Health. 2009;99:65–67. doi:
On September 11, 2001, 2 airplanes crashed
into the World Trade Center towers in New
York City as part of a terrorist attack. In addi-
tion to the loss of life, survivors were ex-
posed to hazardous dust and debris from the
collapse of the buildings, and many people
endured psychological trauma.1–4No one has
definitively determined the number of persons
present in the 2 towers at 8:46 AM on that day
when the first airplane crashed into the North
Tower, and no one may ever be able to do so.
but none made use of capture–recapture
methods, which are useful in estimating popula-
tion size when enumeration by more-direct
methods is not feasible.8–10
My objective was to apply the capture–
recapture method to 3 list sources of individ-
uals determined to be present inside the World
Trade Center towers on September 11 to esti-
matethe number presentwhen the first airplane
struck. This number represents a population at
risk for long-term health effects as a result of
direct exposure to the events of the day.
The World Trade Center Health Registry
(WTCHR) is a database used for following up
with individuals exposed to the disaster of
September 11 to evaluate the short- and long-
term physical and mental health effects. Ex-
posed groups, including rescue and recovery
workers, residents, students and school staff,
building occupants, and passersby, were lo-
cated and interviewed. Potentially eligible in-
dividuals were identified through a multitude
of list sources and could also register through
the project Web site or toll-free telephone
number. In all, 71437 interviews were com-
pleted, including 8965 with individuals present
in the World Trade Center towers at 8:46 AM
on September 11.
Those present in the towers—a group with
high potential for physical and psychological
trauma as a result of exposure to the events
of the day—were identified from 3 different
list sources for the WTCHR. The first list
included 3622 individuals who volunteered
by Web site or telephone to complete the
WTCHR survey (the self-identified list), and
were confirmed to be present in the buildings
on September11. The second list included data
RESEARCH AND PRACTICE
January 2009, Vol 99, No. 1 | American Journal of Public Health
Murphy | Peer Reviewed | Research and Practice | 65