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Preventive
Medicine and
Public Health
PreTest
®
Self-Assessment and Review
PRE
TEST
®
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NOTICE
Medicine is an ever-changing science. As new research and clinical experience
broaden our knowledge, changes in treatment and drug therapy are required. The
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respect accurate or complete, and they disclaim all responsibility for any errors or
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changes have not been made in the recommended dose or in the contraindications
for administration. This recommendation is of particular importance in connection
with new or infrequently used drugs.
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Preventive Medicine
and Public Health
PreTest
®
Self-Assessment and Review
Ninth Edition
SYLVIE RATELLE, M.D.,M.P.H.
Director
STD/HIV Prevention Training Center of New England
Medical Consultant
Division of Sexually Transmitted Diseases Prevention
Massachusetts Department of Public Health, Boston, Massachusetts
Assistant Professor
Department of Family and Community Medicine
Associate Director, Preventive Medicine Residency Program
University of Massachusetts School of Medicine, Worcester, Massachusetts
STUDENT REVIEWERS
NATALIE F. H OLT
Yale University School of Medicine, New Haven, Connecticut
LUCY CHIE
MEGAN SCHWARZMAN
University of Massachusetts School of Medicine, Worcester, Massachusetts
McGraw-Hill
Health Professions Division
PreTest
®

Series
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PRE
TEST
®
7214_Ratelle_fm_mj.qxd 9/15/00 3:42 PM Page iii
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or otherwise.
DOI: 10.1036/0071376399
Terms of Use
CONTENTS
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
BIOSTATISTICS AND METHODS OF EPIDEMIOLOGY
Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Answers, Explanations, and References . . . . . . . . . . . . . . . . . . . . . . 34
EPIDEMIOLOGY AND PREVENTION OF COMMUNICABLE DISEASES
Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Answers, Explanations, and References . . . . . . . . . . . . . . . . . . . . . . 92
ENVIRONMENTAL AND OCCUPATIONAL HEALTH

Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
Answers, Explanations, and References . . . . . . . . . . . . . . . . . . . . . 135
EPIDEMIOLOGY AND PREVENTION OF NONCOMMUNICABLE
AND
C
HRONIC DISEASES
Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
Answers, Explanations, and References . . . . . . . . . . . . . . . . . . . . . 174
PROVISION OF HEALTH SERVICES
Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
Answers, Explanations, and References . . . . . . . . . . . . . . . . . . . . . 205
LEGAL AND ETHICAL ISSUES
Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
Answers, Explanations, and References . . . . . . . . . . . . . . . . . . . . . 223
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
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Terms of Use
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vii
PREFACE
Many changes have been made in this book from the last edition. I hope it
will be helpful in providing a good review of public health and preventive
medicine. I also hope you will appreciate how applicable this field is in
everyday clinical practice (even biostatistics principles!) and what an
important impact prevention can have on the health of a population. Many
thanks to the medical students, Lucy Chie, Megan Schwarzman, and
Natalie Holt, for their thoughtful comments.
This book is dedicated to my husband, Alain Campbell, M.D., M.S.,
and my daughter, Myriam. Very special thanks for supporting me through-
out this project.

SYLVIE RATELLE, M.D., M.P.H.
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INTRODUCTION
Preventive Medicine and Public Health: PreTest
®
Self-Assessment and Review,
Ninth Edition, has been designed to provide medical students and physicians
with a comprehensive and convenient instrument for self-assessment and
review within the field of epidemiology and public health. The 500 questions
provided have been designed to parallel the format of the questions contained
in Step 2 of the United States Medical Licensing Examination (USMLE).
Each question in the book is accompanied by an answer, a paragraph
explanation, and a specific page reference to either a current journal article,
a textbook, or both. A bibliography that lists all the sources used in the
book follows the last chapter.
Perhaps the most effective way to use this book is to allow yourself one
minute to answer each question in a given chapter; as you proceed, indi-
cate your answer beside each question. By following this suggestion, you
will be approximating the time limits imposed by licensing examinations.
When you practice your examination-taking skills with this PreTest
®
,
one way to maximize your score is to go through, answer all the questions
you find easy, and skip over the more difficult ones initially. We do recom-
mend, however, that once you come back to the more difficult questions,
you spend as much time as you need. You will then be more likely to retain
the information. Do note: When it comes to your examination for the board,
you will do better to answer each question as you come to it and not skip
around. Do not spend too much time on any one problem. Make a guess,

circle the question, and come back to it. Otherwise, you can waste time
looking for the questions you skipped or—the ultimate tragedy—you may
discover time is running out.
When you have finished answering the questions in a chapter, you
should then spend as much time as you need verifying your answers and
carefully reading the explanations. Although you should pay special atten-
tion to the explanations for the questions you answered incorrectly, you
should read every explanation. The author of this book has designed the
explanations to reinforce and supplement the information tested by the
questions. If, after reading the explanations for a given chapter, you feel
you need still more information about the material covered, you may wish
to consult the references indicated.
ix
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BIOSTATISTICS AND
METHODS OF
EPIDEMIOLOGY
Questions
DIRECTIONS: Each item below contains a question or incomplete
statement followed by suggested responses. Select the one best response to
each question.
1
1. Assuming that mammography
has a sensitivity of 90% and a
specificity of 98% and that consec-
utive tests are independent, what is
the probability that a woman with
breast cancer will have a negative
yearly screening mammogram for

two consecutive years?
a. 1/10
b. 2/10
c. 4/10
d. 1/100
e. 4/100
2. The association between low
birth weight and maternal smok-
ing during pregnancy can be stud-
ied by obtaining smoking histories
from women at the time of the
first prenatal visit and then subse-
quently assessing and assigning
birth weight at delivery according
to smoking histories. What type of
study is this?
a. Clinical trial
b. Cross-sectional
c. Prospective cohort
d. Case-control
e. Retrospective cohort
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Terms of Use
3. An investigator wishes to per-
form a randomized clinical trial to
evaluate a new beta blocker as a
treatment for hypertension. To be
eligible for the study, subjects
must have a resting diastolic blood
pressure of at least 90 mm Hg.

One hundred patients seen at the
screening clinic with this level of
hypertension are recruited for the
study and make appointments
with the study nurse. When the
nurse obtains their blood pressure
two weeks later, only 65 of them
have diastolic blood pressures of
90 mm Hg or more. The most
likely explanation for this is
a. Spontaneous resolution
b. Regression toward the mean
c. Baseline drift
d. Measurement error
e. Hawthorne effect
4. Which of the following mea-
sures is used frequently as a denom-
inator to calculate the incidence rate
of a disease?
a. Number of cases observed
b. Number of new cases observed
c. Number of asymptomatic cases
d. Person-years of observation
e. Persons lost to follow-up
5. Among women aged 18 to 34 in
a community, weight is normally
distributed with a mean of 52 kg
and a standard deviation of 7.5 kg.
What percentage of women will
have a weight over 59.5 kg?

a. 2%
b. 5%
c. 10%
d. 16%
e. 32%
6. In nine families surveyed, the
numbers of children per family
were 4, 6, 2, 2, 4, 3, 2, 1, and 7.
The mean, median, and mode
numbers of children per family are,
respectively,
a. 3.4, 2, 3
b. 3, 3.4, 2
c. 3, 3, 2
d. 2, 3.5, 3
e. 3.4, 3, 2
2 Preventive Medicine and Public Health
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Biostatistics and Methods of Epidemiology 3
Hypertension Normal Blood Pressure Total
>8 cups 6 4 10
No coffee 2 7 9
81119
7. A study is undertaken to determine whether drinking more than eight
cups of coffee a day is associated with hypertension. The blood pressure
readings were taken of persons who drink more than eight cups and per-
sons who drink no coffee. The results are as follows:
Which of the following is the most appropriate test to analyze the data?
a. Chi-square test
b. McNemar’s test

c. Fisher’s exact test
d. Student t test
e. Analysis of variance
Items 8–10
The results of a study of the incidence of pulmonary tuberculosis in a
village in India are given in the following table. All persons in the village are
examined during two surveys made two years apart, and the number of
new cases was used to determine the incidence rate.
Category of Household Number of Number of
at First Survey Persons New Cases
With culture-positive case 500 10
Without culture-positive case 10,000 10
8. What is the incidence of new cases per 1000 person-years in house-
holds that had a culture-positive case during the first survey?
a. 0.02
b. 0.01
c. 1.0
d. 10
e. 20
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9. What is the incidence of new
cases per 1000 person-years in
households that did not have a
culture-positive case during the
first survey?
a. 0.001
b. 0.1
c. 0.5
d. 1.0
e. 5.0

10. What is the relative risk of
acquiring tuberculosis in house-
holds with a culture-positive case
compared with households with-
out tuberculosis?
a. 0.05
b. 0.5
c. 2.0
d. 10
e. 20
11. In the study of the cause of a
disease, the essential difference be-
tween an experimental study and
an observational study is that in the
experimental investigation
a. The study is prospective
b. The study is retrospective
c. The study and control groups are of
equal size
d. The study and control groups are
selected on the basis of history of
exposure to the suspected causal
factor
e. The investigators determine who is
and who is not exposed to the sus-
pected causal factor
Items 12–13
About 1% of boys are born
with undescended testes. To deter-
mine whether prenatal exposure to

tobacco smoke is a cause of un-
descended testes in newborns, the
mothers of 100 newborns with
undescended testes and those of
100 newborns whose testes had
descended were questioned about
smoking habits during pregnancy.
The study revealed an odds ratio of
2.6 associated with exposure to
smoke, with 95% confidence inter-
vals (CI) from 1.1 to 5.3.
12. Some reviewers are concerned
that the study may overestimate
the association between maternal
smoking and undescended testes in
the offspring because of potential
a. Confounding
b. Nondifferential misclassification
c. Differential misclassification
d. Selection bias
e. Loss to follow-up
4 Preventive Medicine and Public Health
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13. What is the most appropriate
conclusion to be drawn from the
study?
a. There is no association between
maternal smoking and undescended
testes in the offspring
b. The study results, if accurate, sug-

gest that an offspring whose mother
smoked is about 2.6 times more
likely to be born with undescended
testes than an offspring whose
mother did not smoke
c. The p value > 0.05
d. The 90% confidence interval for
these results would probably include
1.0
e. A larger sample size would increase
the confidence interval
14. The probability of being born
with condition A is 0.10 and the
probability of being born with con-
dition B is 0.50. If conditions A and
B are independent, what is the
probability of being born with
either condition A or condition B
(or both)?
a. 0.05
b. 0.40
c. 0.50
d. 0.55
e. 0.60
15. As an epidemiologist, you are
asked to recommend the type of
study appropriate to the needs of
researchers who would like to
study the causes of a rare form of
sarcoma. They have discovered a

registry of this form of cancer and
have access to the largest database
of patients with this form of cancer,
which, unfortunately, is only a few
years old. They have funding for
only one year from the National
Institutes of Health and note the
budget will be tight. What type of
study design do you recommend?
a. Prospective cohort
b. Retrospective cohort
c. Cross-sectional
d. Experimental
e. Case-control
16. If rapidly progressive cancers
are missed by a screening test, which
type of bias will occur?
a. Lead-time bias
b. Length bias
c. Selection bias
d. Surveillance bias
e. Information bias
Biostatistics and Methods of Epidemiology 5
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Items 17–19
Lou Stewells, a pioneer in the study of diarrheal disease, has developed
a new diagnostic test for cholera. When his agent is added to the stool, the
organisms develop a characteristic ring around them. (He calls it the “Ring-
Around-the-Cholera” [RAC] test.) He performs the test on 100 patients
known to have cholera and 100 patients known not to have cholera with

the following results:
6 Preventive Medicine and Public Health
17. Which of the following statements is INCORRECT about the RAC test?
a. The sensitivity of the test was about 91%
b. The specificity of the test was about 12%
c. The false negative rate was about 9%
d. The predictive value of a positive result cannot be determined from the preced-
ing information
e. The predictive value of a negative result cannot be determined from the pre-
ceding information
18. Dr. Stewells next performs the test on 1000 patients with profuse diar-
rhea:
Cholera No Cholera
RAC test + 91 12
RAC test − 988
Totals 100 100
Cholera No Cholera
RAC test + 312 79
RAC test − 31 578
Totals 343 657
Which of the following statements is correct?
a. The predictive value of a positive result is 31/343
b. The predictive value of a positive result is 79/312
c. The predictive value of a negative result is 578/(578 + 31)
d. The predictive value of a negative test is 578/657
e. The incidence rate of cholera in this population is 343/1000
7214_Ratelle_01_mj.qxd 9/15/00 3:33 PM Page 6
19. The RAC test achieves wide-
spread acceptance. However, with
improvements in hygiene, the prev-

alence of cholera gradually falls from
35 to 5% of hospitalized diarrhea
patients. Which statement about the
effect of this fall in prevalence is
true?
a. The change in prevalence will re-
duce the predictive value of a nega-
tive result
b. The predictive value of a positive
result will decline
c. The specificity of the test is likely to
decline
d. The specificity of the test will in-
crease at the expense of its sensi-
tivity
e. It will have no impact on the pre-
dictive values of the test
20. A randomized clinical trial is
undertaken to examine the effect of
a new combination of antiretroviral
drugs on HIV viral load compared
to usual therapy. Randomization is
used for allocation of subjects to
either treatment or control (usual
care) groups in experimental stud-
ies. Randomization ensures that
a. Assignment occurs by chance
b. Treatment and control (usual care)
groups are alike in all respects
except treatment

c. Bias in observations is eliminated
d. Placebo effects are eliminated
e. An equal number of persons will be
followed in the treatment and con-
trol group
21. In a study of the cause of lung
cancer, patients who had the dis-
ease were matched with controls by
age, sex, place of residence, and
social class. The frequency of ciga-
rette smoking was then compared
in the two groups. What type of
study was this?
a. Prospective cohort
b. Retrospective cohort
c. Clinical trial
d. Case-control
e. Correlation
Items 22–24
The incidence rate of lung can-
cer is 120/100,000 person-years for
smokers and 10/100,000 person-
years for nonsmokers. The preva-
lence of smoking is 20% in the
community.
22. What is the relative risk of
developing lung cancer for smokers
compared with nonsmokers?
a. 5
b. 12

c. 50
d. 100
e. 120
23. What percentage of lung can-
cer can be attributed to smoking?
a. 52%
b. 78%
c. 80%
d. 92%
e. 99%
Biostatistics and Methods of Epidemiology 7
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24. If the prevalence of smoking in
the community was decreased to
10%, the excess incidence rate of
lung cancer that could be averted
in that community would be
a. 11/100,000
b. 22/100,000
c. 50/100,000
d. 60/100,000
e. 110/100,000
25. The Coronary Drug Project was
a randomized trial to evaluate the
efficacy of several lipid-lowering
drugs. The five-year mortality of the
men who adhered to the regimen of
clofibrate (i.e., took 80% of their
medicine or more) was 15%; among
those assigned to the clofibrate

group who were less compliant, it
was 24.6%. The result was highly
statistically significant (p < 0.0001).
From this one can conclude
a. Clofibrate was very beneficial to the
patients who took it reliably
b. Clofibrate is not effective unless
patients take at least 80% of the
recommended doses
c. Either clofibrate or something asso-
ciated with taking it reliably is
strongly associated with reduced
total mortality
d. There was a problem with blinding
in this study
e. Only those who were compliant
should be included in the data
26. The use of matching as a tech-
nique to control for confounding is
most appropriate for which type of
study?
a. A large-scale cohort study
b. A case-control study with a small
number of cases
c. A clinical trial with a factorial
design
d. A cross-sectional study with multi-
ple variables
e. A correlation study with a small
number of countries

Items 27–28
An investigator is designing a
randomized, double-blind, placebo-
controlled clinical trial to see whether
vitamin E will prevent lung cancer.
27. Which technique is likely to
maximize compliance with the allo-
cated regimen?
a. Using the placebo
b. Performing a run-in phase
c. Using intent-to-treat analysis
d. Double blinding the study
e. Limiting the number of subjects
enrolled
8 Preventive Medicine and Public Health
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28. Which is most likely to affect
the validity (source of bias) of the
study?
a. Loss to follow-up
b. Incidence of lung cancer
c. Prevalence of smoking in the source
population
d. α error
e. β error
29. The crude death rate in the
United States is 150/100,000. The
crude death rate in a smaller, devel-
oping country is 75/100,000. Based
on these data, which one of the fol-

lowing statements best explains the
data?
a. The health care system of the devel-
oping country is far better than that
in the United States
b. More people die in the United
States because it has a larger popu-
lation
c. Infant mortality in the first week is
higher in developing countries, but
it is not included in the crude death
rate
d. Death rates in the developing coun-
try are lower due to the emigration
effect
e. Crude death rates are usually higher
in developed countries because of a
higher proportion of older persons
in the population
Items 30–32
A research team wishes to in-
vestigate a possible association be-
tween smokeless tobacco and oral
lesions among professional baseball
players. At spring training camp,
they ask each baseball player about
current and past use of smokeless
tobacco, cigarettes, and alcohol,
and a dentist notes the type and
extent of the lesions in the mouth.

30. What type of study is this?
a. Case-control
b. Cross-sectional
c. Prospective cohort
d. Clinical trial
e. Retrospective cohort
Biostatistics and Methods of Epidemiology 9
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31. After the players have been questioned about use of smokeless tobacco
and examined for lesions of the mouth, the data on the 146 players are tab-
ulated as follows:
10 Preventive Medicine and Public Health
Mouth No
Lesion Lesion Total
User 80 30 110
Nonuser 2 34 36
Total 82 64 146
In this study, which measure of disease occurrence can be calculated?
a. Incidence rate
b. Cumulative incidence rate
c. Incidence density
d. Prevalence
e. Relative risk
32. Which of the following statements is true?
a. The odds ratio is equal to (80/110) × (2/36) = 13.1
b. A temporal association between smokeless tobacco use and oral lesions can be
established
c. The statistical association can be calculated using the chi-square test
d. Selection bias could overestimate the result
e. There should be an equal number of exposed and nonexposed subjects

33. A randomized trial shows that a new thrombolytic agent reduces total
mortality by 30% in the first 30 days after a suspected myocardial infarc-
tion compared with a placebo (p = 0.002). Which of the following ques-
tions would be the most important to have answered?
a. Was the trial blinded?
b. What was the power of the study?
c. What happened to surviving patients in the next year?
d. What percentage of patients in each group actually had a myocardial infarction?
e. What was the effect on mortality from coronary heart disease?
7214_Ratelle_01_mj.qxd 9/15/00 3:33 PM Page 10
Items 34–36
In a study of the effectiveness of pertussis vaccine in preventing per-
tussis (whooping cough), the following data were collected by studying
siblings of children who had the disease.
Biostatistics and Methods of Epidemiology 11
Immunization Status Number of Siblings Number of Cases
of Sibling Contact Exposed to Case among Siblings
Complete 4000 400
None 1000 400
34. What was the secondary attack rate of pertussis in fully immunized
household contacts?
a. 0%
b. 10%
c. 25%
d. 40%
e. 75%
35. What was the protective efficacy of whooping cough vaccine?
a. 25%
b. 40%
c. 75%

d. 90%
e. 99%
36. What was the relative risk of contracting whooping cough in the unim-
munized children compared with the fully immunized children?
a. 0.25
b. 0.5
c. 1.0
d. 2.0
e. 4.0
7214_Ratelle_01_mj.qxd 9/15/00 3:33 PM Page 11
37. Decision analyses often include a patient’s utilities in the determina-
tion of the best decision. These utilities measure
a. Whether a patient favors one decision over another
b. Whether a physician favors one decision over another
c. The difference between a patient’s decision and the physician’s decision
d. The relative value a patient places on a particular outcome
e. The relative likelihood of a particular outcome
38. You have just finished conducting a case-control study to measure the
association between alcohol use and lower respiratory tract infections. The
most appropriate method to control for smoking as a confounder is
a. Matching
b. Restriction
c. Randomization
d. Stratification
e. Multivariate modeling
Items 39–41
Data from an investigation of an epidemic of rubella in a remote village
in Brazil are given in the following table:
12 Preventive Medicine and Public Health
Number

Not III
but with
Age Number Number Antibody
Group in Ill Rise Number Percent
(years) Population (Symptomatic) (Asymptomatic) Uninfected Infected
0–9 204 110 74 20 90
10–19 129 70 46 13 90
20–39 161 88 57 16 90
40–59 78 42 28 8 90
60+ 42 2 2 38 10
Totals 614 312 207 95
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39. Which expression represents the calculation to determine the inci-
dence of illness (symptomatic cases) for all age groups (as a percentage)?
a. 95/519 × 100% = 18.3%
b. 207/614 × 100% = 33.7%
c. 207/519 × 100% = 39.9%
d. 312/614 × 100% = 50.8%
e. 519/614 × 100% = 84.5%
40. Which expression represents the calculation to determine the percent-
age of infection that is asymptomatic (subclinical)?
a. 95/519 × 100% = 18.3%
b. 207/614 × 100% = 33.7%
c. 207/519 × 100% = 39.9%
d. 312/614 × 100% = 50.8%
e. 519/614 × 100% = 84.5%
41. Based on the age-specific infection rates, when did German measles
previously occur in this village in relation to the current epidemic?
a. 0 to 9 years ago
b. 10 to 19 years ago

c. 20 to 39 years ago
d. 40 to 59 years ago
e. 60 or more years ago
Items 42–44
A new test has been developed to screen for ovarian cancer. The fol-
lowing figure illustrates the distribution of values for this test among two
populations.
Biostatistics and Methods of Epidemiology 13
Normal population
Population
with cancer
Frequency
0 1015202530354045505560 70
␮g/dL
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