Sample exam questions for Introduction to Epidemiology and Public Health
ANWERS
1.
To be causally associated with disease, the etiological factor should fulfill the following criteria:
Indicate all that apply.




The factor is present in all subjects with the disease.
Elimination of the factor reduces risk of the disease.
The exposure to this factor should precede the development of the disease.
The factor is more prevalent among those with the disease than among those without the
disease.
2.
At the start of a cohort study the exposure is determined with the help of a questionnaire. During
the study there is no "loss to follow-up". At the end of the follow-up time the number of cases is
known and is divided into exposed and unexposed. The odds ratio (OR) is used as the
association measure. Which comment is the most appropriate here? Anwer: a
a.
b.
c.
d.
3.
Researchers should have better calculated the risk ratio (=incidence proportion ratio).
The OR has no useful interpretation.
Researchers should have better calculated the incidence rate ratio.
The OR approaches the incidence rate ratio.
During a study of 20 years five people are followed to measure the occurrence of upper
respiratory tract infection. As this infection can occur more than once, all disease events are
included in this study.

1 person is lost to follow-up after 1.5 years.

2 persons died respectively after 10 and 15 years from a different cause.

1 person got the first respiratory tract infection after seven years and the second infection
after 12 years of follow-up. Both infections take half a year of recovery. This person is
followed-up until the end of the study.

One person is followed-up the whole period without occurrence of disease.
What is de incidence rate in this study? Answer: b
a.
b.
c.
d.
0.06 per person-year
0.03 per person-year
0.15 per person-year
0.08 per person-year
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4.
What is the fraction of cases with the disease among the exposed that is attributable to the
exposure? Answer: a
Unexposed
Exposed
Disease
9
17
No disease
7
5
a.
b.
c.
d.
5.
The incidence rate (IR) differs from the incidence proportion (IP) because... Answer: b
a.
b.
c.
d.
6.
attributable fraction
attributable risk
population attributable risk percentage
negative predictive value
Precise measurement of exposure is important in epidemiologic research. Namely, when the
exposure is not precisely measured the association between exposure and effect is likely to be...
Answer: c
a.
b.
c.
d.
8.
IP can be assessed in a closed population, IR not.
IR can be assessed in an open population, IP not.
IP takes competing mortality into account; IR does not.
IR can be assessed more precisely than IP
If you want to know the proportion of the disease that could be prevented by eliminating the
exposure in the entire study population, you should calculate the Answer: c
a.
b.
c.
d.
7.
0.27
0.60
0.30
0.77
overestimated
confounded
underestimated
random
Which of the following designs is/are suitable for studying a genetic polymorphism in relation to
risk of diabetes mellitus?
Indicate all that apply.




Case-control study
Cross-sectional study
Cohort study
Randomized, controlled trial
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9.
The Cancer and Steroid Hormone (CASH) study, in which women with breast cancer and a
comparable group of women without breast cancer were asked about their prior use of oral
contraceptives is an example of which type(s) of study?
Indicate all that apply.






clinical trial
cohort study
cross sectional survey
case-control study
observational study
experimental study
10. The precision of an estimate of a relative risk depends on the ... Answer: b
a.
b.
c.
d.
generalisability
size of the study
validity of the study
presence of bias
11. In a cohort study the relative risk for COPD for moderate smokers versus non-smokers was 4.
For heavy smokers compared to non-smokers the relative risk was 10.
What would have been the relative risk for COPD in this study if the heavy smokers were used
as the reference category? Answer: a
a.
b.
c.
d.
for non-smoking 0.1 and for moderate smoking 0.4
for non-smoking 0.2 and for moderate smoking 0.6
for non-smoking 4 and for heavy smoking 10
this cannot be calculated with the available data
12. An epidemiologist in Tanzania wants to study the efficacy of iron supplementation for the
prevention of HIV infection. He wants to make sure that only subjects who are (still) free of HIV
infection are enrolled in his trial. Therefore, he screens a large group of people using a
diagnostic test. Based on the outcome of the test, he decides who could participate in his iron
supplementation trial. For this purpose, it is very important that the diagnostic test has a high...
Answer: d
a.
b.
c.
d.
sensitivity
positive predictive value
specificity
negative predictive value
13. A diabetes test is being applied in a population of 5000 men. Previous evaluation of the diabetes
test in a different population showed a sensitivity of 70% and an specificity of 80%. The
prevalence of diabetes is 0.5%.
What is the diagnostic value of a positive test in this situation? Answer: a
a.
b.
c.
d.
2%
47 %
4%
70 %
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14. Information bias in a cohort study can be avoided by ensuring that...
Indicate all that apply.





no competing diseases do occur.
follow-up is complete.
the persons who assess the disease are not aware of the exposure of the participant.
disease assessment is highly standardized.
the persons who collect the data are not aware of the study hypothesis.
15. A cohort study shows a RR of 1.8 (95% CI 1.4-2.2) for alcohol consumption and breast cancer.
Another cohort study shows a RR of 1.8 (95% CI 0.6-3.5) for smoking and breast cancer.
What can be concluded from the results of this study?
Indicate all that apply.




Both associations are likely to be due to chance.
Both associations are biased.
The study on smoking is probably smaller than the study on alcohol.
Alcohol and smoking both cause breast cancer.
16. When studying diet and risk of chronic diseases, a cohort study generally has the following
advantage compared to a case-control study: Answer: d
a.
b.
c.
d.
Potential confounders can be taken into account
Selection bias does not occur
Various dietary exposures can be studied at the same time
It has higher internal validity
17. What is a disadvantage of a cohort study compared to a clinical trial? Answer: b
a.
b.
c.
d.
The external validity is lower
It is more prone to confounding
It is less suitable for studying clinical outcomes
Participants can drop out during follow-up
18. The Framingham Study, in which a group of residents have been followed since the 1950s to
identify occurrence and risk factors for heart disease, is an example of which type(s) of study?






cohort
case-control
experimental
observational
clinical trial
cross-sectional
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19. Researchers prospectively follow a group of 100 vegetarians and 200 non-vegetarians.
After 30 years of follow-up, 8 of the vegetarians and 20 of the non-vegetarians develop heart
disease. The 95% confidence interval on the relative risk of 0.8 ranges from 0.6 to 0.9.
Select the best statement. Answer: d
a. Vegetarians were 80% less likely to develop heart disease during 30 years of follow-up
compared to. non-vegetarians.
b. The researchers should have calculated an odds ratio rather than a relative risk.
c. The relative risk of 0.8 is not statistically significant as the 95% confidence interval contains
the value 0.8.
d. Vegetarians were 20% less likely to develop heart disease during 30 years of follow-up
compared to non-vegetarians.
20. In the Netherlands there is an increase in the prevalence of cardiovascular diseases.
This is a consequence of Answer: c
a.
b.
c.
d.
deterioration of the food pattern
increase in hypertension
improved treatment
increase in obesity
21. General practitioners decide to intensify pharmacological treatment of patients when their
absolute 10-year risk of cardiovascular mortality exceeds 20%. Which risk factors form the basis
for calculating this absolute risk? Answer: c
a.
b.
c.
d.
Age, gender, smoking, isolated systolic hypertension and serum triglyceride levels
Age, gender, smoking, blood pressure and presence of diabetes mellitus
Age, gender, smoking, systolic blood pressure and serum total cholesterol
Age, gender, smoking, body mass index and family history
22. In a hospital-based study of the association between coffee consumption and the occurrence of
stroke, a group of patients hospitalized after suffering a stroke was compared to a control
population hospitalized for other reasons. The patients hospitalized for stroke were found to
consume significantly more coffee than the controls.
All of the following statements represent possible explanations for the observed positive
association between coffee consumption and stroke, EXCEPT: Answer: b
a. Heavy coffee consumers may also be heavy smokers, so smoking rather than coffee drinking
is the relevant causal factor
b. The patients restricted their coffee intake after suffering a stroke.
c. The hospitalized controls consume less coffee, on the average, than individuals in the general
population, resulting in a spurious association between coffee consumption and stroke.
d. Excessive coffee consumption can cause a stroke.
23. Select the correct statement concerning the selection of controls in a case-control study
Answer:b
a. Randomization can help assure comparability of cases and controls.
b. Matching can be used to reduce confounding bias.
c. It is best to identify controls with conditions that are related to the outcome in the case-control
study.
d. It is less important to assure comparability of cases and controls in a case control study than
comparability of study arms in a randomized controlled trial.
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24. In a case-control study the association was examined between smoking and risk of Parkinson's
disease. The table below provides the results. Which of the following odds ratios is correct?
Answer: a
Controls
Cases
Smokers
55
30
Non smokers
45
70
a.
b.
c.
d.
0.35
2.85
1.83
0.55
25. Indicate three types of cancers that are most frequently occurring in Westernized countries.






lymphoma
bladder cancer
cervical cancer
colon cancer
prostate cancer
breast cancer
26. An epidemiologist performed a double-blind, randomized, placebo-controlled trial to examine the
effect of fish oil supplementation on memory complaints. In the group that received fish oil, 19%
of the participants forgot to take their daily supplements during the study whereas this was only
3% in the placebo group. Is this a problem? Answer: b
a. Yes, because this affects the external validity of the study.
b. Yes, because the study outcome can be biased.
c. No, because participants and investigators were blinded towards the type of treatment in both
groups
d. No, because all confounders were equally distributed over both groups due to randomization
27. An epidemiologist wants to assess the effect of tea drinking on blood pressure. He decides to do
an intervention study.
Which of the following measures does not increase the internal validity of the study? Answer: d
a.
b.
c.
d.
Careful monitoring of blood pressure during the study
Inclusion of a control group
Randomization
Random selection of participants from the general population
28. The main advantage of a randomized controlled trial (RTC) compared to all other epidemiology
study designs is that the RCT: Answer: a
a. equally distributes characteristics that may be independent risk factors for the outcome of
interest over the study arms.
b. is prospective thereby eliminating the need for historical data.
c. is less expensive.
d. guarantees that confounding bias will not occur.
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29. A pharmaceutical company showed the following in an article: "1500 subjects with a cold were
treated with our new medicine. Within three days, 95% were asymptomatic and this result was
statistically significant." The company claims the new medicine was effective.
Is this conclusion justified? Answer: c
a.
b.
c.
d.
Yes, because the effect was very large (95% of the subjects benefitted from treatment).
No, because statistical significance indicates that the null hypothesis ("no effect") was correct.
No, because no control group was involved in the study.
Yes, because the effect of treatment could not be explained by chance.
30. Public health surveillance includes various activities.
Which one is not part of public health surveillance? Answer: c
a.
b.
c.
d.
Data collection
Data dissemination
Disease control
Data analysis
31. The problem of confounding can be solved by... Answer: c
a.
b.
c.
d.
choosing a prospective design.
increasing the precision of the measurements.
stratification during data analysis.
this cannot be solved.
32. Consider a population of three persons. For each of the members the life expectancy at birth is
80 and this does not change by age. Answer: d



Person A is a man who gets COPD at the age of 30, reducing his quality of life from 1.0 to
0.3. This man dies at the age of 80.
Person B is a woman who gets a depression at the age of 25, reducing her reducing her
quality of life from 1.0 to 0.5. She recovers from her depression at the age of 35. At the age of
60 she dies because of a heart attack.
Person C is a man who gets lung cancer at the age of 60, reducing his quality of life from 1.0
to 0.1. This man dies at the age of 65.
The number of DALY’s lost in each person’s life history can be calculated.
By combining all life histories in this population of three persons, the population health in terms of
DALY’s can be described for this population.
Which of the following combination is correct?
a
In the life history of person A 35 DALY’s are lost and the total loss of DALY’s for the population
of three is 70
b
In the life history of person A 15 DALY’s are lost and the total loss of DALY’s for the population
of three is 55,5
c
In the life history of person B 5 DALY’s are lost and the total loss of DALY’s for the population of
three is 9,5
d
In the life history of person C 19,5 DALY’s are lost and the total loss of DALY’s for the
population of three is 795
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33. In a study on the prevalence of disease X in nursing homes A and B you get the following data.
Nursing home A = index 1
Persons Number of cases Prevalence rate
with disease X
(per 100)
Age
Young
200
4
2.0
Old
400
24
6.0
Total
600
28
4.7
Nursing home B = index 2
Persons Number of cases Prevalence rate
with disease X
(per 100)
Age
Young
800
24
3.0
Old
100
8
8.0
Total
900
32
3.6
Nursing home A + B = standard Persons Number of cases Prevalence rate
with disease X
(per 100)
Age
Young
Old
Total
One can calculate the standardized prevalence rate and comparative mortality figure (CMF) by
means of direct standardization, using the joint population of nursing home A and B as the
standard. Which calculation is correct? Answer: a
a.
b.
c.
d.
The standardized rate of nursing home A is 3.3/100
The CMF of nursing home A is 0.97
The standardized rate of nursing home A is 2.4/100
The standardized rate of nursing home B is 6.3/10
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