Practice Problems--Midterm
The following problems are similar to those that will appear on your
midterm examination. The answers to the problems are given at the end
of this lesson
Use the following information for questions 1 and 2.
An outbreak of gastritis occurred on a cruise ship. The following data
were obtained from a questionnaire completed by everybody on board
the ship shortly after the outbreak:
Food
Herring
Chicken
Spinach soufflé
Oysters
Chocolate mousse
1.
2.
Persons who
ate food
Sick
Well
200
800
650
350
200
800
300
700
600
400
Persons who did not
eat food
Sick
Well
100
900
100
900
500
500
400
600
450
550
What is the most likely infective food on the cruise ship?
a.
Herring.
b.
Chicken.
c.
Spinach soufflé.
d.
Oysters.
e.
Chocolate mousse.
What is an estimate of the relative risk of developing gastritis
associated with herring consumption?
a.
0.5
b.
2.0
c.
2.3
d.
8.0
e.
It cannot be computed from the data given.
3.
4.
5.
California Highway Patrol statistics revealed that more accidents
involve blue cars than cars of any other color. The inference that
while driving a blue car one is at higher risk of an accident than while
driving a car of another color is
a.
correct.
b.
incorrect, because the comparison is not based on rates.
c.
incorrect, because no control or comparison group is used.
d.
incorrect, because no test of statistical significance has been
made.
e.
incorrect, because prevalence is used instead of incidence.
In 1945, 1,000 women were identified who worked in a factory
painting radium dials on watches. The incidence of bone cancer in
these women up through 1975 was compared to that of 2,000 women
who worked as telephone operators in 1945 (assume all 3,000 women
were followed for the entire 30 years and that the two groups were
identical in all respects except for their occupation). Twenty of the
radium dial workers and four of the telephone operators developed
bone cancer between 1945 and 1975. An estimate of the relative risk
of developing bone cancer for radium dial workers is
a.
2.
b.
4.
c.
5.
d.
10.
e.
not possible to compute from the data given.
When a new treatment is developed that reduces case fatality for a
particular disease, but does not produce recovery from that disease,
which of the following will probably occur?
a.
Prevalence of the disease will decrease.
b.
Incidence of the disease will increase.
c.
Prevalence of the disease will increase.
d.
Incidence of the disease will decrease.
e.
Incidence and prevalence of the disease will decrease.
Use the following information for questions 6–10.
Regionville is a community of 100,000 persons. During 1990, there
were 1,000 deaths from all causes. All clinically diagnosed cases of
tuberculosis during 1990 have been found, and they total 300, of
which 200 were males and 100 were females. During 1990, there were
60 deaths from tuberculosis, 50 of them in males.
6.
7.
8.
9.
Crude mortality rate in Regionville in 1990 was
a.
300 per 100,000.
b.
60 per 100,000.
c.
10 per 1,000.
d.
100 per 1,000.
e.
not possible to compute from the data given.
The proportionate mortality in 1990 due to tuberculosis is
a.
20 percent.
b.
30 percent.
c.
6 percent.
d.
3 percent.
e.
not possible to compute from the data given.
An estimate of the tuberculosis case fatality in 1990 would be
a.
6 percent.
b.
20 percent.
c.
2 percent.
d.
equal in males and females.
e.
higher in females than in males.
The mortality rate in 1990 due to tuberculosis was
a.
60 per 100,000 per year.
b.
300 per 100,000 per year.
c.
200 per 1,000 per year.
d.
20 percent.
e.
not possible to compute from the data given.
10. The mortality rate in 1990 due to tuberculosis in males was
a.
0.5 per 1,000 per year.
b.
25 percent.
c.
greater in males than in females.
d.
50 per 300 per year.
e.
not possible to compute from the data given.
11. Communities P and Q have equal age-adjusted all-cause mortality
rates. Community P has a lower crude mortality rate than Q. The best
conclusion is that
a.
the two communities have identical age distributions.
b.
diagnosis is more accurate in P than Q.
c.
P has an older population than Q.
d.
Diagnosis is less accurate in Q than P.
e.
P has a younger population than Q.
12. In three large series of cases of disease, the gender distribution was
found to be as follows:
Series
1
2
3
Total
Male cases
200
250
450
900
Female cases
100
50
150
300
The incidence rate of this disease, by gender, was
a.
twice as great in males as in females.
b.
three time greater in males than in females.
c.
five times greater in males than in females.
d.
from two to five times as great in males as in females.
e.
not possible to compute from the data given.
Use the following information to answer questions 13–16.
A large study of bladder cancer and cigarette smoking in Boston
produced the following data:
Cigarette smokers
Nonsmokers
Bladder cancer incidence
rates per 100,000 males
48.0
25.4
13. The relative risk of developing bladder cancer for male cigarette
smokers compared with male non-smokers is
a.
48.0.
b.
22.6 per 100,000 male smokers per year.
c.
1.89.
d.
47.1 percent.
e.
not possible to compute from the data given.
14. Assume that cigarette smoking is a cause of bladder cancer. The
attributable risk of bladder cancer due to cigarette smoking in male
cigarette smokers is
a.
1.89.
b.
22.6 per 100,000 male smokers per year.
c.
141.
d.
48.0 per 100,000 male smokers per year.
e.
not possible to compute from the data given.
15. Assume that cigarette smoking is a cause of bladder cancer. The
population attributable risk percent for bladder cancer due to
smoking in males in Boston is
a.
48.0.
b.
22.6 per 100,000 per year.
c.
1.89.
d.
47.1 percent.
e.
not possible to compute from the data given.
16. Assume that cigarette smoking is a cause of bladder cancer, and that
during the time that this study was conducted 300 cases of bladder
cancer were diagnosed among male smokers in Boston. About how
many of these cases occurred because these men were smokers?
a.
1.89.
b.
22.6 per 100,000 per year.
c.
48.0.
d.
141.
e.
It cannot be computed from the data given.
17. A community-wide x-ray survey was conducted in a rural county in
the first week of June 1945 in order to identify persons with active
tuberculosis.
Race
White
Black
Population
surveyed
22,608
15,582
Active cases
found
379
189
Active cases
per 1,000
16.8
12.1
The results of this survey were interpreted as contradicting the widely
held view that blacks are more prone to develop active tuberculosis
than whites. This interpretation is
a.
justified given the data.
b.
not justified given the data.
18. In 1960, the blood pressure of a group of 500 men aged 21 to 24 was
examined. The same men were re-examined every five years for the
next 30 years. The results are shown in the following table:
Year of
examination
1960
1965
1970
1975
1980
1985
1990
Age at time of each
examination
21–24
25–30
31–35
36–40
41–45
46–50
51–55
Number
of men
500
500
500
500
500
500
500
Mean diastolic
blood pressure
75
80
81
85
89
94
98
Choose the one best answer: these data show that in this sample of
men,
a.
diastolic blood pressure rose in all men with increasing age.
b.
no statement concerning the relationship of age to blood
pressure can be made from these data because the cohort effect
is not known.
c.
no statement concerning the relationship of age to blood
pressure can be made from these data because the effect of
selective survival is unknown.
d.
none of the above statements is correct.
19. Approximately 11.4% of the deaths in children aged 1–14 years in the
United States in 1989 were due to cancer. Approximately one-quarter
of the deaths among persons 65 years of age or older were due to
cancer in that year. Is it correct to say that these data indicate that the
risk of death from cancer was approximately twice as great in the
older age group than the younger age group?
a.
Yes.
b.
No.
20. Most cancer incidence statistics for the United States come from
areas with population-based cancer registries. Age-specific incidence
rates are computed by enumerating the number of new cases in a
given age group during a certain time period, and dividing by the
estimated mid-time period population in that age group.
From 1960 to 1975, the annual number of hysterectomies performed
on American women increased much faster than the size of the
female population aged 15 and over. Virtually all of the increase was
accounted for by hysterectomies done for nonmalignant indications.
What effect would you predict this trend would have on the observed
case fatality for uterine cancer?
a.
The case fatality would be too high.
b.
The case fatality would be too low.
c.
The case fatality would not change.
d.
It depends on the difference in treatments among women with
hysterectomies and without hysterectomies.
e.
None of the above.
21. Suppose that the incidence rate of a particular disease is the same in
every county in Washington State, and that the frequency of a
particular exposure (suspected as a possible risk factor for the
disease) is also the same in every county in Washington State. Would
you be willing to conclude from these data that exposed persons have
the same risk of disease as do unexposed persons? Why or why not?
(Use no more than two brief sentences for your response.)
22. Use the following data to answer parts a, b, and c of this question.
Disease
Oral cancer
Bladder cancer
Stroke
Accidents
All causes
Age-adjusted mortality rates per 1,000 per year
Nonsmokers
Smokers
Total population
2.8
5.6
3.4
7.4
15.6
8.3
14.6
15.9
15.2
11.4
12.3
12.0
25.6
33.4
28.7
Assuming that smoking is a cause of death due to stroke, oral cancer,
and bladder cancer, answer the following questions:
a.
What is the rate of fatal stroke in the total population that is
attributable to smoking?
b.
What is the rate of fatal oral cancer in smokers relative to
nonsmokers?
c.
What percentage of deaths due to bladder cancer would be
prevented if no one in this population had smoked cigarettes?
23. In 1987, Feldman et al. studied the descriptive epidemiology of
cancer in the state of Connecticut (MMWR 36:205–7, 1987). They
used data from the Connecticut Tumor Registry, a population-based
surveillance system that since 1935 has (1) identified all new cancer
diagnoses in Connecticut residents, and (2) followed them to evaluate
prognosis. The authors estimated various measures of frequency of
all cancers combined. The following table is based on their report.
Measure
Incidence1
Prevalence2
Mortality1
Males
463
1,789
246
Gender
Females
342
2,222
154
1 age-adjusted rate per 100,000 per year (for 1981–82)
2 age-adjusted per 100,000 on January 1, 1982
One or more of these aspects could be explained
a.
by a greater prevalence of cancer risk factors among males
compared to females, and a tendency for females to develop
cancers that are more lethal than those developed by males.
b.
by a tendency for females to develop cancers that are less lethal
than those that males develop.
c.
only by looking at age-specific data.
d.
by the ecologic fallacy.
e.
by none of the above.
Questions 24 and 25 concern the following information from a recent
report from the CDC (MMWR 41:225–28, 1992):
In October 1991, a woman reported that her son and at least 10 other
persons who had recently participated in a high school biology field
trip to a seaside state park had developed pruritic dermatitis
(“swimmer’s itch”). The state epidemiologist conducted an
investigation of 37 persons who had contact with the sea water during
the trip, of whom 30 met the case definition for the outbreak. Among
her findings were that (1) cases occurred among 5 of 11 persons who
had worn long pants in the water, as opposed to 25 of 26 persons who
had worn shorts in the water, and (2) cases occurred among 16 of 19
persons who reported promptly drying the exposed skin with a towel,
compared with 14 of 18 who did not promptly dry skin with a towel.
24. An estimate of the relative risk of developing swimmer’s itch
associated with wearing long pants as opposed to short pants in this
outbreak would be
a.
0.47.
b.
0.03.
c.
2.00.
d.
30.0.
e.
0.81.
25. Based on the data, reasonable advice that the state epidemiologist
could have given to the park officials would be to recommend that
waders
a.
dry off promptly after going in the water.
b.
wear long pants (or similar protective clothing).
c.
dry off promptly only if one has worn shorts in the water.
d.
wear short pants.
Questions 26 and 27 are based on the following summary of a recent
report from the CDC:
A recent report examined the epidemiology of traumatic injuries from
helicopter crashes during logging operations in Alaska (MMWR
43:472–75, 1994). Between (and including) July 1991 and December
1992, there were 50 helicopter pilots and 25 helicopters involved in
logging operations. During this time period, 6 helicopters crashed
during logging operations; these crashes resulted in 4 pilot deaths.
26. The crash rate per 100 helicopter-months was
a.
6.0.
b.
1.3.
c.
24.0.
d.
0.013.
e.
16 percent.
27. The mortality rate for helicopter pilots per 100,000 pilot-years was
a.
5,333.
b.
10,666.
c.
0.533.
d.
8,000.
e.
9.0.
28. Down’s syndrome is one of the most serious and frequently reported
birth defects among live-born infants and is an important cause of
mental retardation. It is well-established that the prevalence of
Down’s syndrome at birth increases with increasing maternal age, but
few other risk factors have been identified. Investigators at the
Centers for Disease Control and Prevention recently examined
geographic patterns of Down’s syndrome in the United States in an
attempt to generate clues to the etiology of this disease (MMWR
43:617–22, 1994). The data were derived from population-based
surveillance systems in eight states during 1983–90 (inclusive).
Down’s syndrome at birth, by state, 1983–90
State
Number of cases
Number of live births
New Jersey
625
687,387
New York
2,121
2,157,413
Illinois
246
375,896
Kansas
184
319,696
Georgia
272
269,332
Maryland
327
437,704
Colorado
131
106,172
Washington
246
217,808
The patterns in the prevalence of Down’s syndrome at birth based on
these data would be consistent with which one of the following
statements?
a.
The prevalence in Colorado is high because it has the fewest
number of cases among the states studies.
b.
The prevalence in Kansas is particularly low because births are
ascertained less completely in that state compared to the others
under study.
c.
The difference between the prevalences in Kansas and Colorado
could be due, at least in part, to greater underreporting of
Down’s syndrome in Colorado compared to Kansas.
d.
The variation among the eight states could be due to differences
in the age distribution of the mothers giving birth in the
different populations during the study period.
e.
The variation among the eight states could not be due to
differences in the age distribution of the mothers giving birth in
the different populations during the study period.
29. Investigators at the Centers for Disease Control and Prevention
recently examined time trends in the occurrence of low birthweight
(LBW) infants (MMWR 43:335–39, 1994). The data were derived
from birth certificates for live-born U.S. infants during 1981–91.
LBW infants were categorized according to whether or not they were
term gestations or pre-term gestations, and trends by year were
examined. (See the following graph.)
Incidence of low birthweight, by gestation and year of birth
80
70
60
50
Term
Pre-term
Total
40
30
20
10
0
81
82
83
84
85
86
87
88
89
90
91
Year of Birth
Conclusions that would be consistent with the one or more aspects
of this analysis include all of the following except
a.
the incidence of LBW infants increased during 1981–91 largely
as a result of increases in the incidence of LBW pre-term.
b.
the trends could be due to the increasing presence, in the U.S.
population of pregnant women, of risk factors for pre-termassociated LBW during the study period.
c.
the incidence of LBW probably increased during 1981–91
because the number of births increased during that time period.
d.
risk factors for term LBW probably did not increase in the U.S.
population of pregnant women during the study period.
e.
the majority of the increase in the incidence of pre-term LBW
appears to have occurred since about 1987–88.
Answers to the Practice Midterm Problems
1.
b
2.
b
3.
b
4.
d
5.
c
6.
c
7.
c
8.
b
9.
a
10.
e
11.
e
12.
e
13.
c
14. b
15.
e
16.
d
17. b
18.
d
19. b
20.
c
21.
No—such a
conclusion would
be based on the
ecologic fallacy
22. (a) 0.6 per 1,000
per year; (b) 2.0;
(c) 10.8%
23. b
24.
a
25. b
26. b
27.
a
28.
d
29.
c