An epidemiological investigation was begun on July 1, 2000 among a population of 1,000 individuals. Three individuals were found to have leukemia on July 1st. During the ten-year follow-up period, five new cases of leukemia were diagnosed. Among the eight leukemia cases, four deaths occurred during the ten-year follow-up period.
Two additional individuals, neither of whom had leukemia, were lost to follow-up at some point during follow-up. None of the remaining 990 study participants became ill, died, or were lost to follow-up during the follow-up period.
The diagram below indicates the experience of the 10 study participants, using the following symbols:
*
:case recognition (diagnosis of leukemia)
*<
:onset of leukemia was prior to start of study period
—-
:observation period during follow-up
X
:status at termination of observation (i.e., alive, dead, lost)
case
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
1
—
–*–
—–
—–
—–
—–
—–
—–
—–
—–
–X
alive
2
—
——
—–
–*–
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