Course material

1. Epidemiology: (PUBH – 6035 – 2) Module 3 Problem Set
Question 1 Recently, a report was published describing a string of cases of Norwalk virus
gastroenteritis among passengers on cruise ships. From this report, an epidemiologist went
on to form a number of hypotheses as to why there had been this rather unusual increase in
reported gastroenteritis outbreaks on cruise ships in 2012. The cruise ship owners
contacted the Centers of Disease control and Prevention (CDC) to conduct an in-depth
analysis of the possible modes of transmission of the Norwalk virus in the cruise ship
environment. CDC investigators interviewed all of the passengers on the last affected cruise
(N=3,000) and obtained information on the passenger’s recreational activities. They found
the following results: 1,000 passengers had gone swimming in the upper deck pool and
2,000 passengers had never gone swimming in the upper deck pool. 100 of the passengers
who swam in the upper deck pool and 100 of the passengers who did not swim in this pool
developed Norwalk virus gastroenteritis during the cruise. FYI: The cruise lasted one week.·
Set up the 2×2 table for these data.· Calculate the risk ratio of gastroenteritis associated
with swimming in the upper deck pool.· State in words your interpretation of the above risk
ratio· Calculate the risk difference in the above example· State in words your interpretation
of the above risk differenceQuestion 2 For this problem, note the following chart: Age
Group(in years)% of Population in Age GroupInfluenza Rate per 1,000 person-years There
are 10,000 individuals in City A, which is located in Massachusetts. Eight young individuals
and 420 old individuals develop the flu over the course of a year.· Use these data to calculate
the crude influenza rate per 1,000 individuals per years in City A.· What is the crude rate of
influenza in City B?· What is the crude rate of influenza in City C?· Calculate an age-adjusted
influenza rate for each of the cities. Use the age distribution for the State of Massachusetts
(shown in the table) as the standard.Question 3 Recently, Australian researchers conducted
a study of the relationship between optimism and colon cancer survival. Their hypothesis
was that colon cancer patients who had a positive outlook on life would have a lower five-
year cumulative incidence of mortality. The study included 100 recently diagnosed colon
cancer patients who underwent psychological testing and were found to have a optimistic
outlook on life and 100 recently diagnosed colon cancer patients who underwent the same
psychological tests and were found to have a pessimistic outlook on life. By the end of five
years of follow-up, 50 of the 100 patients with the optimistic outlook and 75 of the 100
patients with the pessimistic outlook had died from colon cancer.· Set up and fill in the two

2. by two table using these data.· What is the prevalence of colon cancer in the study
population?· Compare the cumulative incidence of mortality in the optimistic group to the
cumulative incidence of mortality in the pessimistic group using a ratio measure of
association.· State in words your interpretation of the result you found in part c.