Epidemiologic Principles

Midterm Exam
March 15, 2005
Answer in space provided. You may use the backs of pages for scrap and calculations.
Covers Chapters 1, 2, 4, 6, 7, 9
1. Reliability. Two raters on a hiring committee screen applications to determine if the
candidates will be go on to an interview. Two-hundred twenty-six (226) candidates are
screened, with results shown below. The kappa (6) statistic for these data is 0.46.
RATER A
+
-

RATER B
+
65
31
28
102

a. Is the agreement perfect? (circle)

Yes

No

b. Is the agreement better than random? (circle)

Yes

No

c. How good is the agreement? (One sentence response.)

2. Incidence and prevalence. A cohort of 1000 people begins with 10 prevalent cases. Over the
next 2 years, 20 incident cases arise.
a. What is the prevalence of disease at the start of the follow-up period? (Provide numerator
and denominator no need to complete the quotient.)

b. What is the risk (incidence proportion) of disease over the follow-up interval?
(Numerator and denominator only.)

c. What is the rate of disease over the follow-up interval? (Numerator and denominator.)

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3. Sensitivity & specificity. A screening test for a preclinical stage of a cancer is known to have
a sensitivity of .90 (i.e., 90%) and a specificity of .96 (i.e., 96%). The prevalence of this
cancer in its preclinical phase in the population is 1 per 1000 (.001). Assume we use this test
in one-hundred thousand (100,000) people. Based on this information, determine:
a. the total number with disease =

_______

b. the number of true positives =

_______

c. the number of true negatives =

_______

d. the number of false negatives =

_______

e. the number of false positives =

_______

f. the total number of test positives =

_______

Comment: If you wish, you can set up the data in a 2-by-2 table to help with your calculations.
(Table will not be graded.)

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4. Vital statistics. Use the data in the table below to calculate the following vital statistics.
(Complete calculations and report final results, as indicated.)
Vital statistics for problem on this page
Total midyear population
Number of live births
Total deaths (all cause)
Deaths in infants under 1 year of age
Deaths due to cancer

50,000
500
425
5
100

a. crude mortality rate (per 100,000)

b. cancer mortality rate (per 100,000)

c. infant mortality rate (per 1,000)

d. Assuming immigration and emigration are balanced and death rates are constant, and
basing your answers on the reported births and deaths, is this population stationary
(steady-state)? (circle)
Yes

No

e. Justify your answer to d.

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5. Age-adjustment. Age-stratified data for two populations are:

Population A
Age Group

Population B

Cases

Persons

198

99,000

Old

1,000

All

203

100,000

Young

Age Group

Cases

Persons

1,000

Old

990

99,000

All

991

100,000

Young

a. Which of the populations, A or B, has the higher crude death rate? By how much? (Look
at the data.)

b. In the younger age group, which population, A or B, has the higher age-specific death
rates. By how much? (You will need to complete elementary calculations before
answering this question.)

c. In the older age group, which population, A or B, has the higher age-specific death rates.
By how much? (Some calculation required.)

d. Question deleted . . .

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6.

7.

Study Design 1. Read the following passages. Then, answer the questions below. Questionnaires were mailed to
every 10th person listed in the city telephone directory. Each person was asked to list age, sex, smoking habits,
and respiratory symptoms during the preceding seven days. About 20% of the questionnaires were completed
and returned. About 10% of respondents reported having upper respiratory symptoms.
a.

Is this study experimental or observational? (circle)

b.

Justify the choice you made in a.

c.

Is this study an ecological study? (circle)

d.

Justify the choice you made in c.

e.

Is this study longitudinal or cross-sectional? (circle)

f.

Justify the choice you made in e.

g.

Classify the study (circle single best choice):

experimental

observational

yes

no

longitudinal

cross-sectional

a) randomized trial
c) cohort
e) cross-sectional

b) non-randomized trial
d) case-control
f) ecological

Study Design 2. 1,500 employees of a major aircraft company were initially examined in 1951 and were
classified by diagnostic criteria for coronary artery disease (CAD). New cases of CAD have been identified by
examinations every three years and through death certificates. Incidence rates in different subgroups have been
computed.
a.

Is this study experimental or observational?

experimental

observational

b.

Is this study an ecological study?

yes

no

c.

Is this study longitudinal or cross-sectional?

longitudinal

cross-sectional

d.

Is this a case-control study?

yes

no

e.

Classify the study? (circle single best choice):

a) randomized trial
c) cohort
e) cross-sectional

b) non-randomized trial
d) case-control
f) ecological

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Multiple Choice and Matching

1.

Match the term with its brief description.

___
___
___
___

public health
epidemiology
pathology
morbidity

List the causes of death in correct rank order as

of 1990 (p. 8).
___
___
___
___

a. Victorian (19th century) surgeon /

anesthesiologist who became quintessential
epidemiologic hero; known for innovative theory
about waterborne theory of cholera
b. First Registrar General for national vital
statistics system; miasmaist who was late to adopt
contagion theory

d. 17th century habadasher; first to use morbidity

and mortality data for demographic and
epidemiologic purposes
6.

a. delay onset or reduce severity

b. slow progression or prevent sequelae
c. prevent new occurrences
7.

This marks the beginning of the subclinical stage

of disease.
a. exposure to the ultimate agent
b. first symptoms
c. diagnosis
d. resolution of symptoms

W hat does it mean when an epidemiologist says

there is "interdependence" between factors?

a. there is a spectrum of effects

b. multiple factors act together to result in an
effect
c. there is a long induction period
d. much of the disease goes unnoticed or
unreported

Match the goal of each type of prevention

___ primary
___ secondary
___ tertiary

Morbidity and mortality patterns associated with

the epidemiologic transition of the 20th century
are characterized a switch from _____________
cause to __________________ cause.
a. acute infectious . . . chronic infectious
b. acute non-infectious . . . chronic infectious
c. acute infectious . . . chronic non-infectious
d. chronic infectious . . . chronic non-infectious

4.

W illiam Farr
John Snow
Sir Richard Doll
John Graunt

c. 20th century Brit known for studies about

smoking and health

first
second
third
forth

a. cancer
b. cardiovascular
c. unintention injuries
d. chronic lung diseases (e.g. COPD)
3.

Match the British epidemiologist with their brief

bio.
___
___
___
___

a. study of health and disease on a population

basis
b. organized activity to prevent disease and
promote health
c. study of disease
d. related to disease or disability
2.

5.

8.

How long is the incubation period for HIV and

AIDS?
a. a number of hours
b. a number of days
c. a number of weeks
d. a number of years

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9.

Put the stages in the natural history of disease in

correct chronological order
___
___
___
___

15. Match the term with its brief descriptor.

___
___
___
___

first
second
third
fourth

Agent
Host factor
Environmental factor
Epidemiologic homeostasis

a. external conditions other than the agent

b. inherent factors that influence the
susceptibility to disease or likelihood of exposure
c. the balance of factors determining the level of
disease in a population
d. a biologic, physical, or chemical cause

a. subclinical
b. susceptibility
c. clinical
d. recovery, disability, or death
10. Match the term with its brief description.

16. Match the concept with its brief description.

___
___
___
___

iceberg phenomenon
spectrum of disease
induction
latency

___
___
___
___

a. broad range of manifestations and severities

b. health problem largely undetected
c. time between causal action and initiation
d. time between disease initiation and detection
11. Causal factor rarely (if ever) acts alone.
a. True
b. False
12. The incidence of a disease depends on the
prevalence of complementary factors in the
population.

Causal web
Sufficient/component cause model
Spectrum of disease
Epidemiologic iceberg

a. Diseases have a broad range of manifestations

and severities
b. Causal factors combine to complete causal
mechanisms
c. A large percentage of a problem is unreported
or hidden from view.
d. Direct and indirect causes form complex
hierarchal interrelations
17. W hich of the following factors can lead to an
epidemic?

13. Select the most accurate statement.

a. increases in susceptibility
b. environmental factors that favor propagation
or retention of the agent
c. increases in the pathogenicity of agents
d. all of the above

a. Phenylketonuria is a genetic disease caused by

an inborn error in metabolism.
b. Phenylketonuria is an environmental disease
caused by the consumption of phenyketones.
c. both A & B
d. neither A nor B

18. The factors of a 1) slippery surface, 2) brittle

bones, and 3) use of a psychoactive drug that
causes loss of equilibrium contribute to a
particular hip fracture. W hat is the causal
complement to the slippery surface?

a. True
b. False

14. Smoking is a *necessary* factor in the cause of

lung cancer.
a. True
b. False

a. brittle bones
b. use of the psychoactive drug
c. brittle bones + use of the psychoactive drug
d. fracture

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