Epidemology Textbook Readings
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University of Ottawa *
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HSS 4303
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Medicine
Date
Dec 6, 2023
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Chapter 1
1. Define each of the following terms:
a.
Public health
i.
Public health is a multidisciplinary field whose goal is to promote the health of
populations through organized community efforts.
b.
Epidemiology
i.
Epidemiology is the study of the distribution and determinants of disease frequency
in human populations and the application of this study to control health problems.
Disease refers to a broad array of health-related states and events, including
diseases, injuries, disabilities, and death
c.
Population
i.
. A population is a group of people with a common characteristic.
d.
.Disease frequency
i.
A measure of disease frequency quantifies how often a disease arises in a
population. Its calculation involves establishing the disease definition, developing a
mechanism for counting the diseased cases (the numerator), and determining the
size of the underlying population (the denominator).
e.
Disease distribution
i.
ii.
Disease distribution refers to the pattern of disease according to the characteristics
of person (Who is getting the disease?), place (Where is it occurring?) and time (How
is it changing over time?)
f.
Disease determinants
i.
Disease determinants are factors that cause either a healthy person to become sick
or a sick person to recover
g.
Disease control
i.
Disease control is the ultimate aim of epidemiology refers to the reduction or
elimination of disease occurrence. It is accomplished through epidemiological
research and surveillance.z
h.
.Hypothesis
i.
A hypothesis is a tentative explanation for an observation, a phenomenon, or a
scientific problem that can be tested by further investigation.
2.
What is the primary difference between public health and medicine?
-
Public health focuses on preventing diseases in communities, and medicine focuses on
treating diseases at the individual level.
3.
What public health achievements have accounted for improved life expectancy in the
United States over the past century?
-
Public health achievements that have improved life expectancy include the routine use of
vaccinations for infectious diseases, improved sanitation and clean water, modification of risk
factors for coronary heart disease and stroke, improved access to family planning and
contraceptive services, and antismoking campaigns
What are the main objectives of epidemiology?
-
The main objectives of epidemiology are to study the natural course of disease, determine
the extent of disease in a population, identify patterns and trends in disease occurrence,
identify the causes of disease, and evaluate the effectiveness of measures that prevent and
treat disease.
How do epidemiologists quantify the disease frequency in a population?
-
Epidemiologists quantify the frequency of disease by developing a definition of the disease,
instituting a mechanism for counting cases of disease within a population, and determining
the size of that population. It is only when the number of cases are related to the size of the
population that we know the true frequency of disease.
State the contribution that was made by each of the following historical figures:
a.
John Graunt
i.
John Graunt summarized the patterns of mortality in 17th-century London and
discovered the regularity of deaths and births.
b.
John Snow
i.
John Snow conducted one of the first observational studies in the neighborhoods of
19th-century London and discovered that contaminated drinking water was the cause
of cholera
c.
Richard Doll and Austin Bradford Hill
i.
Richard Doll and Austin Bradford Hill conducted groundbreaking studies on cigarette
smoking and lung cancer in the 1950s
d.
James Lind
i.
James Lind conducted one of the earliest experimental studies on the treatment of
scurvy among sailors. Using E. sound experimental principles, he found that the
consumption of oranges and lemons was the most effective remedy for scurvy in this
population.
e.
William Farr
i.
William Farr was the compiler of Statistical Abstracts in Great Britain from 1839
through 1880. In this capacity, he pioneered many activities encompassed by
modern epidemiology, including the calculation of mortality rates using census data
for denominators
How are the many subspecialities of modern epidemiology typically defined?
. Today’s subspecialties are defined in terms of the exposure (e.g., environmental exposures), the
disease (e.g., cancer), and the population being studied (e.g., the elderly)
In which three directions has modern epidemiological research expanded?
. Modern epidemiology examines risk factors at the molecular level (e.g., biological markers of
exposure, genetic markers), the societal level (e.g., social factors such as racism), and across the
life span (from birth through old age).
Chapter 2
1. What measure of disease frequency is each of the following?
A.
The percentage of freshman girls who become pregnant over the course of their high
school years
-
Cumulative incidence
B.
The percentage of senior boys who are fathers at the time of graduation
-
Prevelence
C.
The number of live-born babies who die of sudden infant death syndrome during the
first year of life per e. 100,000 baby-years of follow-up
-
Incidence Rate
D.
The percentage of infants weighing less than 2500 grams at birth The lifetime risk of
breast cancer
-
Prevelence
E.
The lifetime risk of breast cancer
-
Cumulative incidence
2. Briefly describe the main similarities and differences between each of the following
a.
Prevalence and incidence
i.
Prevalence quantifies existing cases; incidence quantifies new cases.
b.
Incidence rate and cumulative incidence
i.
The main similarity is that they both quantify the number of new cases of
disease that develop in a population at risk during a specified period of time.
The main difference is that the incidence rate is a true rate that directly
integrates person-time of observation into the denominator, and cumulative
incidence is a proportion whose denominator is the population at risk at the
start C. of the observation period. Time in cumulative incidence is expressed
only by words that go along with the proportion.
c.
Fixed and dynamic populations
i.
A dynamic population is defined by a changeable state A. or condition, and
therefore its membership is transitory; B. a fixed population is defined by a life
event, and C. therefore its membership is permanent.
3. What are the lowest and highest possible values of each of the following measures of
disease frequency?
a.
Prevalence
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-
0% and 100%
b.
Cumulative incidence
-
0% and 100%
c.
Incidence rate
-
Zero and infinity. Infinity is, in theory, the highest value of the incidence rate
when person-time is essentially zero. This could happen, for instance, if
everyone in a population died instantaneously following a highly D. noxious
exposure (e.g., cyanide).
4. Suppose tphat there were 2900 new cases of breast cancer diagnosed among women in
Boston, Massachusetts, and 200 new cases diagnosed among women in Anchorage, Alaska,
in 2017. Based on these data, is it accurate to say that the incidence rate of breast cancer is
higher in Boston than Anchorage? Why or why not?
-
No. It is also necessary to know the size of the population and the amount of follow-up
time in each city.
5. A study of 100 injection drug users who tested negative for HIV infection at enrollment had
their HIV status retested at 3-month intervals over a 2-year follow-up period. All of the
injection drug users were followed for the entire 2-year period. None died and none were lost
to follow-up. Which of the following frequency measures of HIV infection can be calculated at
the end of the study?
a. Prevalence
b. Cumulative incidence
C. Incidence rate
d. All of the above
6. Consider a class with 100 enrolled students. None of the students were ill at the beginning
of the school year. On September 30, a total of 5 students reported having gastroenteritis. All
5 continued to be ill on October 1, but all 5 recovered within 3 days. On October 14, another 3
students developed gastroenteritis. All of these students continued to be ill on October 15,
but all 3 recovered 5 days later. In this example, assume that a person cannot get
gastroenteritis more than once.
a.
Calculate the prevalence of gastroenteritis in the class on October 1
i.
5/100
b.
Calculate the prevalence of gastroenteritis in the class on October 30.
i.
0/100
c.
Calculate the cumulative incidence of gastroenteritis in the class during the month of
October.
i.
3(100-5)=3/95. Remember that only the population at risk at the beginning of
october is eligible for the denominator
7. The incidence rate of a nonfatal disease is 500/100,000 person-years. People usually have
the disease for an average of 3 years, at which time the disease resolves spontaneously.
Estimate the prevalence of this disease using this information. Assume that the population is
in steady state.
-
When the population is in steady state, P = IR × D, where P is prevalence, IR is
incidence rate, and D is average duration. Thus, P = 500/100,000 person-years × 3
years or 1,500/100,000.
8. A population of 100 healthy men was followed for the development of prostate cancer.
After being followed for 5 years, 20 men developed prostate cancer. Another 10 men were
followed for 1 year and then were lost. The remaining men who never developed the disease
were followed for 10 years. Calculate the number of person-years of observation accrued by
this population.
-
(20 × 5 years) + (10 × 1 year) + (70 × 10 years) = 100 + 10 + 700 = 810 person-years
9. Consider the following hypothetical data on the occurrence of hepatitis in two cities:
a.
Calculate the cumulative incidence of hepatitis in each city.
i.
City A = 25/25,000 over 1 year or 50/50,000 over 1 year. City B = 30/50,000 over
1 year.
b.
Which city has the higher cumulative incidence?
i.
City A has the higher cumulative incidence.
10. A total of 60 cases of myocardial infarction were reported over a period of 2 years in a
city with a population of 100,000 people. Using these data, estimate the incidence rate of
myocardial infarction per 100,000 person-years. State any assumptions that are needed.
-
The following calculation assumes that everyone is followed for the entire 2 years and
that all cases occurred at the end of the second year: 60/(100,000 persons × 2 years) =
60/200,000 person-years or 30/100,000 person-years. Different assumptions can be
made regarding the length of follow-up for cases and noncases and the time of case
occurrence.
11. The incidence rate of postpartum depression among 250,000 women who recently
experienced a pregnancy was 12 cases per 100,000 woman-years of follow-up. Exactly how
many incident cases of postpartum depression developed in this population?
-
The incidence rate was 12/100,000 person-years, which is equivalent to x /250,000
person-years. Solving for x , we arrive at 30 new cases.
12. State the type of population (fixed or dynamic) that best describes each of the following:
A.
People who live in New York City
a.
Dynamic. This is a changeable condition; people are continually entering and
leaving the city.
B.
Male residents of Paris who had coronary bypass surgery between 2010 and 2017
a.
Fixed. This is a permanent characteristic; once a man has the surgery, he is
forever part of this group.
C.
Children residing in California who were vaccinated against polio in 1955
a.
Fixed. This is also a permanent characteristic; same rationale as answer
D.
Women who are practicing physicians in the United States
a.
Dynamic. This is a changeable characteristic. New graduates are entering
practice, others are leaving by C. retirement, and so on.
13. How does each of the following conditions influence the prevalence of a disease in a
population? For each scenario, assume that no other changes occur. Your choices are
increases prevalence, decreases prevalence, or has no effect on prevalence.
A.
a cheap new clinical test becomes widely available that allows doctors to diagnose
previously latent (i.e., c. hidden) disease.
a.
Increases prevalence
B.
A new treatment is developed that cures people of the disease very soon after they
are diagnosed.
a.
Decreases prevalence
C.
There is migration of a large number of healthy people into the population.
a.
Decreases prevalence
14. Indicate whether the following statements are true or false:
a.
Only the population at risk contributes to the denominator of the cumulative
incidence.
i.
True
b.
When calculating the incidence rate of a disease, it is necessary to follow all subjects
for the same length of time.
i.
False
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c.
If the incidence rate of a very serious disease is d. 75/100,000 person-years and the
prevalence of this disease in the population is 25/100,000, then the average duration
of this disease must be 3 years.
i.
False
d.
All other things being equal, when a new prevention measure for a disease is
developed, the prevalence of the disease will decrease over time.
i.
True
e.
All other things being equal, when a treatment is developed that prolongs the life of
people suffering from a disease, the prevalence of the disease will increase over time.
i.
True
15. An epidemiological investigation that was started on January 1, 2017, identified a
population of 1,000 individuals among whom 4 were found to have the disease under study.
During the year of the study, 6 new cases were found. Among the total of 10 cases, there
were 6 deaths during the year. For the 10 cases, the diagram indicates the time of case
recognition, periods of observation during the study, and vital status at the time of the
termination of observation. An arrow at the start of the diagram (subjects 1, 2, 3, 4) indicates
that the start of disease occurred before the study began. Assume that the 990 remaining
individuals in the study did not become ill or die during the year of observation. From the
information and diagram given, calculate the following:
a.
Prevalence of the disease on January 1, 2017; July 1, 2017; and December 31, 2017
i.
4/1,000.
ii.
6/996. Remember that the population size has decreased by 4 because of
death.
iii.
4/994. Again, the population is smaller
b.
Cumulative incidence of disease during 2017
i.
6/996. Only those who do not have the disease of interest are at risk.
c.
Cumulative incidence of death during 2017
i.
6/1,000. Everyone in the population is at risk of dying.
Chapter 3
1. Describe the main similarity and difference between each of the following:
a.
Incidence rate ratio and incidence rate difference
i.
They are both ways to compare measures of disease frequency to assess the
effect of an exposure on a disease. The ratio measure gives information on the
strength of the relationship between an exposure and a disease; the difference
measure describes the excess number of cases of disease that are associated
with the exposure.
b.
Risk difference and population risk difference
i.
Both provide information on the absolute effect of the exposure or the excess
risk of disease. However, the risk difference gives the number of cases of
disease among the exposed that may be attributable to the exposure, and the
population risk difference gives the number of cases of disease in the total
population that may be attributable to the exposure.
2 Suppose that an investigation of the association between regular physical activity and
ovarian cancer revealed that the incidence rate of ovarian cancer among women who
engaged in regular physical activity was 30 per 100,000 woman-years of follow-up, whereas
the rate among women who did not engage in regular activity was 45 per 100,000
woman-years of follow-up.
a.
Use these data to compute the incidence rate ratio of c. ovarian cancer for women
who are physically active versus women who are not.
i.
30/100,000 person-years/45/100,000 person-years = 0.67.
b.
State in words your interpretation of this measure.
i.
Women who engage in regular physical activity have C. 0.67 times the risk of
ovarian cancer (or a 33% reduced risk of ovarian cancer) compared with
women who do not engage in regular physical activity.
c.
Compute the incidence rate difference of ovarian cancer for women who are
physically active versus women who are not.
i.
30/100,000 person-years - 45/100,000 person-years = -15/100,000 person-years.
Note that the incidence rate difference is negative.
d.
State in words your interpretation of this measure.
i.
The excess rate of ovarian cancer among women who do not engage in regular
physical activity is 15/100,000 person-years. Or, if regular physical activity
prevents E. ovarian cancer, then 15 cases per 100,000 person-years of
follow-up would be eliminated if the women engaged in regular physical
activity.
e.
If there were no association between regular physical activity and ovarian cancer,
what would be the numeric values of the incidence rate ratio and incidence rate
difference?
-
Null value for the incidence rate ratio is 1.0, and the null value for the incidence
rate difference is 0.0.
3. State the main difference between a crude rate and an ageadjusted rate.
-
A crude rate describes the disease frequency in a population using only raw data. For
example, a crude prevalence is calculated by dividing the total number of cases in the
population at a point in time by the total number of individuals in the population at a
point in time. An ageadjusted rate is a summary rate used to compare disease
frequencies across populations with different age distributions. Often, direct
standardization is used to calculate age-adjusted rates.
4. State the main difference between an age-specific rate and an age-adjusted rate.
-
An age-specific rate is a rate that applies only to a particular age group. For example,
the incidence rate of HIV infection among 15to 24-year-olds is an age-specific rate. As
described above, an age-adjusted rate is a summary rate that accounts for the age
differences when comparing populations. The numeric value of the age-adjusted rate
depends on the particular weights used for the adjustment.
5.Consider the following heart disease mortality data from two hypothetical countries,
including a low-income and a high-income country.
a.
Use these data to calculate the overall crude death rates from heart disease in the
hypothetical highand low-income countries.
i.
Crude heart disease death rate in the low-income country equals (0.30 ×
2/100,000 person-years) + (0.40 × 20/100,000 person-years) + (0.30 × 40/100,000
person-years) = 20.6/100,000 person-years. Crude heart disease death rate in
the high-income country equals (0.20 × 2/100,000 person-years) + (0.30 ×
20/100,000 person-years) + (0.50 × 40/100,000 personyears) = 26.4/100,000
person-years.
b.
Based on these data, do you think that it is better to compare the heart disease death
rates in the two countries using the overall crude rate or the agestandardized rate for
each country? Briefly justify your answer
i.
The age-adjusted rate is better because the age structures of the two
populations are different.
6. The 58th annual convention of the American Legion was held in Philadelphia from July 21
until July 24, 1976. People at the convention included American Legion delegates, their
families, and other Legionnaires who were not official delegates. Between July 20 and August
30, some of those who had been present became ill with a type of pneumonia that was
subsequently named Legionnaires’ disease. No one attending the convention developed the
disease after August 30. The numbers of delegates and nondelegates who developed
Legionnaires’ disease during the period July 20 to August 30 (a 41-day period) are as follows:
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a.
Compute the cumulative incidence of Legionnaires’ disease among delegates and
nondelegates.
i.
Cumulative incidence (CI) among the delegates equals a/(a + b) = 125/1,849 =
0.068 (in 41 days). CI among the nondelegates equals c/(c + d) = 3/762 = 0.004
(in 41 days).
b.
Calculate the cumulative incidence ratio of Legionnaires’ disease among delegates
compared with nondelegates
i.
Cumulative incidence ratio equals
CI delegates /CI nondelegates = 0.068/0.004 = 17.0.
c.
State in words the meaning of this measure.
i.
The risk of Legionnaires’ disease was 17 times greater among delegates than
among nondelegates. Or, a delegate had 17 times the risk of contracting
Legionnaires’ disease as did a nondelegate.
d.
Calculate the cumulative incidence difference of Legionnaires’ disease among
delegates compared with nondelegates.
i.
Cumulative incidence difference equals CI CI nondelegates delegates = 0.068 -
0.004 = 0.064 (in 41 days)
e.
State in words the meaning of this measure.
i.
If delegate status is a “cause” of Legionnaires’ disease, then 64 cases per
1,000 delegates would be eliminated if the delegates had been nondelegates.
Note that delegate status is not the actual cause of Legionnaires’ disease but
reflects which part of the hotel that the individual entered during the
convention. Further investigation found that the organism that causes
Legionnaires’ disease was present in certain air conditioners.
f.
Calculate the attributable proportion of Legionnaires’ disease among the delegates.
i.
Attributable proportion equals [(CI delegates - CI nondelegates/ CI delegates ]
× 100% =[(0.068 - 0.004)/0.068] = 94%
g.
State in words the meaning of this measure.
i.
This means that 94% of the cases of Legionnaires’ disease among the
delegates could be attributed to their delegate status.
7. Indicate whether the following statements are true or false.
a.
When there is no association between an exposure and a disease, the numerical value
of the risk ratio will be zero.
i.
False
b.
When there is no asssociation between an exposure and a disease, the numerical
value of the risk difference will be 1.0
i.
false
c.
A study examined the relationship between air pollution and the risk of having a baby
with low birth weight. The investigators found that the risk ratio comparing pregnant
women exposed to high versus low levels of air pollution was 1.35. This means that
women exposed to high air pollution levels were 35% more likely to have a baby with
low birth weight.
i.
True
d.
A study examined the autopsied brains of 100 professional football players with a
history of repeated concussions. The investigators found that abnormal protein
deposits were present in nearly 100% of the brains. This means that there was an
association between repeated concussions and abnormal protein deposits in the
brains of these athletes.
i.
False
e.
A study examined the relationship between swimming in an unchlorinated pool and
the risk of developing diarrhea. The investigators found a 15% excess risk among
people who swam in the pool compared with those who did not. This means that 15%
of the diarrhea cases among pool users could have been prevented if they had
refrained from swimming in the unchlorinated pool.
i.
True
f.
A study examined the relationship between vitamin supplementation and the
occurrence of asthma among children. The investigators found that compared with
children who did not take vitamins, children who took vitamins on a daily basis were
0.8 times as likely to develop asthma. This means that children who took vitamins
were 80% less likely to develop asthma.
i.
False
8. The incidence rate of migraine headaches was 1.5/100 person-years among overweight
women and 1.0/100 person-years among normal weight women. Using only this information,
state whether you can calculate each of the following measures:
a.
Rate difference
i.
YES
b.
Rate ratio
i.
YES
c.
Attributable proportion among the exposed
i.
YES
d.
Attributable proportion among the total population
i.
NO
(This measure requires information about the proportion of the population
that is exposed.)
9. Consider the following data from a British study of cigarette smoking and mortality among
male physicians (Doll R, Peto R, Boreham J, Sutherland I. Mortality in relation to smoking: 50
years’ observations on male British doctors. Br Med J . 2004;328:1519. doi:10.1136
/bmj.38142.554479.AE). The age-standardized mortality rates (per 100,000 personyears) from
lung cancer and ischemic heart disease are 249 and 1001, respectively, among current
smokers and 17 and 619 among lifelong nonsmokers.
a.
Use these data to calculate the mortality rate ratio and mortality rate difference for
each disease comparing current smokers to lifelong nonsmokers.
i.
The mortality rate ratio and difference for lung cancer are 14.6 and 232/100,000
py, respectively. The mortality rate ratio and difference for ischemic heart
disease are 1.6 and 382/100,000 py, respectively.
b.
Based on your answer to part A, is smoking a stronger risk factor for deaths from lung
cancer or ischemic heart disease?
i.
Smoking is a stronger risk factor for lung cancer than ischemic heart disease
deaths (rate ratios: 14.6 for lung cancer and 1.6 for ischemic heart disease).
c.
Based on your answer to part A, does smoking have a greater public health impact via
deaths from lung cancer or ischemic heart disease? In other words, if smoking were
the cause of mortality, how many deaths from each cause would have been averted if
these individuals had never smoked?
i.
Smoking has a greater public health impact via deaths from ischemic heart
disease than lung cancer (rate differences: 382/100,000 py for heart disease
and 232/100,000 py for lung cancer). This means that 382 deaths from heart
disease for every 100,000 py vs. 232 deaths from lung cancer for every 100,000
py would have been averted if no one had smoked.
d.
Describe the reason(s) for your answers to parts B and C.
i.
The reason for the difference is the higher mortality rate from ischemic heart
disease in the study population. In other words, it is a more common cause of
death than lung cancer among the British male physicians.
Chapter 4
1. Undercounting in the U.S. Census could affect the accuracy of which of the following
epidemiological activities?
a.
Assessing the prevalence of a disease in the U.S. c. population
b.
Assessing the incidence of a disease in the U.S. d. population
c.
Comparing the occurrence of disease in different segments of the U.S. population
d.
All of the above
2. Over the period 2002– 2012, the Centers for Disease Control and Prevention estimated that
the prevalence of autism spectrum disorder in the United States increased by 121% from 6.6
to 14.6 per 1,000 children. Among the possible explanations for this marked increase are
a.
The incidence of the disorder truly increased
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b.
Awareness of the disorder increased and therefore previously unrecognized cases
were more likely to be identified and diagnosed
c.
Both A and B
3. In 2012, the American Psychiatric Association proposed that the definition of autism
spectrum disorder be narrowed. Under their new definition, a person needs to exhibit three
deficits in social interaction and at least two repetitive behaviors. This is a much stricter
standard than previously used. Assuming no changes in diagnosis and reporting, what effect
would having a stricter disease definition have on the incidence of this disorder?
a.
The incidence would increase
b.
The incidence would decrease
c.
The incidence would remain the same
4. The United Nations collects data on infant mortality from over 230 countries around the
world for its annual Demographic Yearbook . The Yearbook defines infant mortality as infant
deaths of liveborn infants under 1 year of age. List two reasons why it is difficult to make
accurate comparisons of infant mortality rates across so many diverse countries.
-
There may be differences in the reliability and completeness of data on infant deaths
and differences in the reliability and completeness of data on livebirths. This includes
undercounting deaths and births because they are not reported to civil registers and
inaccuracies regarding the age of the death.
Chapter 5
1. The following data give some of the descriptive epidemiology of gastroschisis in the state
of Massachusetts. Gastroschisis is a rare birth defect that is characterized by a herniation of
the abdominal wall. Its treatment requires surgical repair.
a.
Based on these data, briefly describe each of the following using words and numbers:
i.
The change in prevalence from 2000 to 2009
1.
There was about a 60% increase in the prevalence of gastroschisis from
2000 through 2009. The ii. increase during 2000– 2005 is steeper than
that during 2006– 2009. In fact, the prevalence decreases slightly from
2006– 2007 to 2008– 2009.
ii.
The trend in prevalence by maternal age
1.
The prevalence of gastroschisis decreased dramatically with maternal
age. It decreased by iii. about 25% from ages 19 and under to 20– 24
years and by another 72% from ages 20– 24 years to 25 years and older.
iii.
The difference in prevalence between Blacks and Whites
1.
The prevalence of gastroschisis was 1.9 times higher among White
mothers as compared with Black mothers.
iv.
The difference in prevalence by gender
1.
The prevalence of gastroschisis was 1.5 times higher among male
infants as compared with female infants
b.
Data such as these are used to generate hypotheses about the causes of disease.
Using any information in the tables, briefly describe a hypothesis that might explain
one of these descriptive features.
There are many possible hypotheses. For example, the prevalence of gastroschisis
increased over time because risk factors for the defect also increased overtime.
Gastroschisis has been associated with maternal alcohol consumption, illicit drug use, and
use of acetaminophen and vasoactive drugs.
c.
Data such as these are also used by public health administrators and planners to
establish priorities, allocate resources, and plan and evaluate the effectiveness of
treatment and prevention programs. Briefly describe how these data might be used to
allocate resources for the prevention and treatment of gastroschisis.
There are many possible answers. For example, these data could be used to support
increased screening activities for gastroschisis among teenaged White women who come to
prenatal care.
2. Define the following terms:
-
Disease cluster
-
A disease cluster is an aggregation of relatively uncommon events or disease
in space and/or time in amounts that are believed or perceived to be greater
than could be expected by chance.
-
Outbreak
-
An outbreak is the occurrence of cases of an illness, specific health-related
behavior, or other health-related events clearly in excess of normal
expectancy. Outbreak is a synonym for epidemic that often refers to a localized
epidemic
-
Epidemic
-
An epidemic is the occurrence of cases of an illness, specific health-related behavior,
or other health-related events clearly in excess of normal expectancy. A worldwide
epidemic is known as a pandemic.
Chapter 6
1. State the main difference between the following study designs:
a.
Observational and experimental studies
i.
In an observational study, the investigator “watches” as subjects themselves
choose which group they will be in (exposed or unexposed); in an
experimental study, the investigator assigns participants to their exposure
groups
b.
Retrospective cohort and prospective
i.
Both the exposures and outcomes have already occurred at the start of a
retrospective cohort study. The outcomes have not yet developed at the start
of a prospective cohort study. Thus, a retrospective cohort study investigates
prior outcomes, and a prospective cohort study investigates future outcomes.
c.
cohort studies Cohort and case– control studies
i.
A cohort study defines subjects according to their exposure level and follows
them for disease occurrence. A case– control study defines cases of disease
and controls and compares their exposure histories.
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2. Briefly describe a cross-sectional study and indicate its main limitation.
-
A cross-sectional study examines the relationship between diseases and other
variables at one particular time. Subjects are commonly selected without regard to
exposure or disease status. Its main limitation is that one cannot infer the temporal
sequence between the exposure and disease
3. Briefly describe the situations in which the hallmark limitation of a cross-sectional study is
avoided.
-
The temporal inference problem in cross-sectional studies is avoided if an unalterable
characteristic, such as a genetic trait, is the focus of the investigation or if the
exposure measure reflects past exposure.
4.Briefly describe an ecological study and indicate its main limitation.
-
An ecological study examines the rates of disease in relation to a population-level
factor. Thus, the units of analysis are populations rather than individuals. The lack of
information about individuals leads to a limitation known as the “ecological fallacy,”
which means that the association observed on an aggregate level does not
necessarily represent the association that exists on the individual level.
5. Briefly describe the situations in which an ecological study may be preferred over other
observational studies.
-
An ecological study is preferred when there is an interest in studying the impact of
contextual effects among communities and cultures. For example, an ecological study
may be preferred for examining the effect of racial segregation on rates of
hypertension in urban communities.
6. State which observational study design is best (i.e., most efficient and logical) in each of
the following scenarios:
a.
Identifying the causes of a rare disease
i.
Case control
b.
Identifying the long-term effects of a rare exposure
i.
Retrospective cohort
c.
Studying the health effects of an exposure for which e. information is difficult and
expensive to obtain
i.
Case control
d.
Identifying the causes of a new disease about which little is known
i.
Case control
e.
Identifying the short-term health effects of a new exposure about which little is known
i.
PROSPECTIVE COHORT
f.
Identifying the causes of a disease with a long latent period
i.
Case control
7. Which type of study is being described in each of the following sce
narios?
a.
study that examines the death rates from colon cancer in each of the 50 U.S. states in
relation to the average percentage of residents in each state undergoing colonoscopy
screening
i.
Ecological
b.
A study that compares the prevalence of back pain among current members of the
automobile manufacturing union with that of current members of the bakers and
confectionary union
i.
Cross-sectional
c.
A study that evaluates the relationship between breast cancer and a woman’s history
of breastfeeding. The investigator selects women with breast cancer and an
age-matched sample of women who live in the same neighborhoods as the women
with breast cancer. Study subjects are interviewed to determine whether they
breastfed any of their children.
i.
Case– control
d.
A study that evaluates two treatments for breast cancer. Women with stage 1 breast
cancer are randomized to receive either cryotherapy (a new treatment involving
extreme cold to kill cancer cells) or traditional lumpectomy. Women are followed for 5
years to determine whether there are any differences in breast cancer recurrence and
survival.
i.
Experimental
e.
A study that began in 2010 of the relationship between exposure to chest irradiation
and subsequent risk of breast cancer. In this study, women who received radiation
therapy for postpartum mastitis (an inflammation of the breast that occurs after giving
birth) in the 1950s were compared with women who received a nonradiation therapy
for postpartum mastitis in the 1950s. The women were followed for 60 years to
determine the incidence rates of breast cancer in each group.
i.
Retrospective cohort
8. Indicate whether the following statements are true or false:
a.
Observational studies of preventions and treatments are often conducted when
experimental studies are unethical or infeasible.
i.
True
b.
The main limitation of observational studies is the investigator’s inability to have
complete control of extraneous factors called confounders.
i.
True
c.
A cross-sectional study of the relationship between blood type and the risk of
cataracts will produce misleading results because you cannot tell the correct temporal
relationship between the exposure (blood type) and disease (cataracts).
i.
False
d.
An ecological study was done to determine the relationship between per capita soft
drink consumption and mortality rates from diabetes in 10 U.S. states. The
investigators found a strong association between soft drink consumption and
diabetes mortality. Based on this study, we can conclude that the individuals who
consumed the soft drinks were the ones who died from diabetes.
i.
False
e.
Case– control studies are inherently inferior to cohort studies.
i.
False
f.
Experimental studies are inherently superior to observational studies.
i.
False
g.
Prospective cohort studies are inherently superior to retrospective cohort studies.
i.
True
Chapter 7
1. Briefly define each of the following terms that are associated with experimental studies:
a.
Randomization
i.
A process by which the investigator assigns subjects to the treatment and
comparison groups. Subjects have an equal chance of being assigned to either
the treatment or comparison group.
b.
Reference population
i.
The group of people to whom the study results may be applied or generalized.
c.
Single-masked study
i.
The study subject does not know whether he or she is in the treatment or
comparison group.
d.
Double-masked study
i.
Both the study subject and the investigator administering the treatment do not
know the subject’s group assignment.
e.
Run-in period
i.
The run-in period occurs before enrollment and randomization to determine
which participants are able to comply with the study regimen. Potential
participants are placed on the test or control treatment for a certain period of
time to assess their tolerance to and acceptance of the treatment and to obtain
information on compliance.
f.
Placebo and sham procedure
i.
A placebo is an inactive substance, such as a sugarcoated pill, that is given as
a substitute for an active substance. A sham is a bogus procedure that is
designed to resemble a legitimate one. Both placebos and sham procedures
permit the study participants and caregivers to be masked.
g.
Equipoise
i.
Equipoise is a state of mind characterized by genuine uncertainty about the
appropriate course of action, that is, to give or withhold a particular treatment.
It is ethical to conduct an experimental study only when there is a state of
equipoise in the expert community.
2. .State the main difference between each of the following:
a.
Individual and community trials
i.
In individual trials, the treatment is allocated to particular people; in
community trials, the treatment is allocated to entire communities.
b.
Preventive and therapeutic trials
i.
Preventive trials investigate measures that stop or delay the onset of disease;
therapeutic trials investigate measures that treat existing disease
c.
Simple and factorial trial designs
i.
. Simple designs test one treatment; factorial designs test two or more
treatments.
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3. Each of the following problems represents a major threat to the validity of an experimental
study. Briefly describe one method for avoiding these problems.
a.
Low compliance
i.
There are several possible answers. For example, design a simple protocol,
enroll motivated and knowledgeable participants, exclude subjects who might
have difficulty complying, present a realistic picture of the required tasks at
enrollment, maintain frequent contact with study subjects, and use items such
as pill packs to make it easier to comply with the treatment regimen.
b.
Lack of baseline comparability
i.
Randomize a large number of study subjects.
c.
Biased information on the outcome
i.
Mask investigators to group assignment.
4. Describe the essential feature and purpose of an intent-totreat analysis.
-
An intent-to-treat analysis includes all individuals who were randomly allocated to the
treatment and comparison groups, regardless of whether they completed or even
received their assigned regimen. This type of analysis preserves the baseline
comparability and gives information on the effectiveness of the treatment under
real-life conditions.
5. What distinctive features of experimental studies enhance their ability to produce
scientifically rigorous results?
-
Unique features include random assignment of subjects to the treatment and
comparison groups to control for confounding and reduce biased allocation and the
use of placebo controls to permit masked assessment of the outcomes.
6. Why are experimental studies difficult to conduct?
-
They are expensive to conduct, physicians and patients may be reluctant to
participate, and a state of equipoise must exist.
7. Indicate whether the following statements are true or false:
a.
A major advantage of a randomized experimental study is that it rules out
self-selection of subjects to the treatment and comparison groups.
i.
True
b.
Randomization controls for confounding equally well in both large and small studies.
i.
False
c.
Noncompliance in an experimental study makes the compared groups more similar,
which reduces the ability of the investigator to detect a difference between the
groups.
i.
True
d.
An important advantage of a placebo-controlled experimental study is that it permits
masking of study subjects and study investigators.
i.
True
e.
Randomization and random selection are alternative terms for the same concept.
i.
False
f.
Some experimental studies are terminated earlier than planned because of a shift in
equipoise.
i.
True
8. In a double-masked study to evaluate the effectiveness of cranberry juice to reduce the
incidence of urinary tract infections (UTIs), participants were randomized to receive cranberry
juice or a placebo beverage twice a day for 6 weeks. The intent-to-treat risk difference
comparing the incidence of UTIs among those randomized to cranberry juice versus placebo
showed an 8% reduction in UTIs among cranberry juice drinkers. Compliance was equally
low (about 60%) in both groups. The risk difference from an efficacy analysis would show:
a.
Greater than 8% reduction in UTIs among cranberry
b.
juice drinkers Less than 8% reduction in UTIs among cranberry juice drinkers
c.
An 8% reduction in UTIs among cranberry juice drinkers
9. Suppose that a small, randomized, single-masked experimental study is conducted. Which
of the following problems are surely avoided in this study?
a.
Noncompliance
i.
-
NO
b.
Confounding
i.
NO
c.
Biased assessment of the disease outcome
i.
NO
d.
Loss to follow-up
i.
NO
10. Suppose that a randomized intervention study of vitamin D supplementation for the
prevention of prostate cancer was conducted among White men aged 50– 64 years living in
the United States. The results of this study are most generalizable to which of the following
groups? Briefly give the reason(s) for your decision.
a.
White men aged 50– 64 years living in the United Kingdom
i.
This is because their baseline risk of prostate cancer is most similar to the U.S.
men in the study. Because race and age greatly influence a man’s risk of
prostate cancer, the results may not be as generalizable to U.S. Black men and
older U.S. men who have higher rates of this cancer. In fact, older men are
more likely to have latent disease, making prevention via vitamin
supplementation less likely.
b.
White men aged 65– 85 living in the United States.
c.
Black men aged 50– 64 years living in the United
Chapter 8
1.
Briefly define each of the following terms that are associated with cohort studies:
a.
Open or dynamic cohort
●
An open, or dynamic, cohort is conducted in a population defined by
a changeable characteristic, such as residence in a specific place.
Thus, its members come and go, depending on whether they have
the characteristic.
b.
Fixed cohort
●
A fixed cohort is defined by an irrevocable event, and therefore it
does not gain any new members
c.
Retrospective cohort study
●
A retrospective cohort study looks back in time and examines
exposures and outcomes that have already occurred by the time the
investigator begins the study.
d.
Prospective cohort study
●
A prospective cohort study looks forward in time and examines
future outcomes in relation to past or current exposures.
e.
Ambidirectional cohort study
●
An ambidirectional cohort study has both prospective and
retrospective components.
f.
Standardized mortality ratio (SMR) study
●
A standardized mortality ratio (SMR) study is a special type of
cohort study in which the mortality experience of an exposed group
is compared with that of the general population. It is commonly
conducted in occupational settings.
2.
State the main similarity and main difference between cohort and experimental
studies.
●
The main similarity is that both types of studies compare two or more
exposure groups, which are followed to monitor outcome rates. The main
difference is that the investigators allocate the exposure in experimental
studies and the participants choose their exposures in cohort studies.
3.
What is the ideal but unattainable comparison group in a cohort study?
●
The ideal but unattainable comparison group would consist of exactly the
same individuals in the exposed group had they not been exposed. This
concept is known as the counterfactual ideal because it is impossible for
the same person to be exposed and unexposed simultaneously.
4.
Describe the strengths and weaknesses of the three types of comparison groups
used in cohort studies. Which one comes closest to the counterfactual ideal?
●
Of the three types of comparison groups, the internal comparison group
comes closest to the counterfactual ideal because it comes from the same
source population as the exposed group and so is most comparable.
However, internal comparison groups are often difficult to identify. The
general population is the next best option mainly because it is stable and
easy to obtain. Its limitations can include lack of comparability to the
exposed group and lack of information on confounders. The comparison
cohort is the least preferable option. Although it may be comparable to the
exposed group, results from such a study are difficult to interpret because
the comparison cohort often has other, possibly noxious, exposures.
5.
Among the following studies, which comparison group comes closest to the
counterfactual ideal?
a.
A study that compares male breast cancer rates among U.S. Marines who
were stationed at Camp Lejeune, North Carolina, and were exposed to
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solvents in the local drinking water with breast cancer rates among men
from the general U.S. population.
b.
A study that compares male breast cancer rates among U.S. Marines who
were stationed at Camp Lejeune, North Carolina, and were exposed to
solvents in the local drinking water with U.S. Marines who were stationed at
Camp Lejeune, North Carolina, but were not exposed to solvents in the
local drinking water.
6.
State whether or not a cohort study is best suited for each of the following
scenarios:
a.
When little is known about a rare exposure
●
Yes
b.
When little is known about a rare diseas
e
●
No
c.
When the study population will be difficult to follow
●
No
d.
When you want to learn about multiple effects of an exposure
●
Yes
7.
Why is it important to minimize losses to follow-up?
●
Losses to follow-up decrease the number of individuals who can be
included in the analysis and therefore reduce the statistical power of the
study. Also, if those who are lost have different rates of disease than those
who remain, the study results may be biased.
8.
How is person-time calculated within the context of a cohort study?
●
Person-time is accrued for each individual in a cohort study. It begins when
the follow-up period of the study begins. It ends when one of the following
occurs: the individual develops the outcome under study, dies, or is lost or
the follow-up period for the study ends.
9.
Indicate whether the following statements are true or false:
a.
A retrospective cohort study is more efficient than a prospective cohort
study for studying diseases with long latent and induction periods.
●
TRUE
b.
Special cohort studies are the most sensible design for examining many
exposures in relation to a single disease.
●
FALSE
c.
Losses to follow-up can be a problem in a cohort study but not in an
experimental study.
●
FALSE
d.
General cohort studies are good for studying common exposures, whereas
special cohorts are good for studying rare ones.
●
TRUE
10. Which of the following techniques that are commonly used in experimental
studies can also be applied in cohort studies?
a.
Masking
●
Yes
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b.
Placebo
●
No
c.
Randomization
●
No
d.
Run-in period
●
No
e.
Intent-to-treat analysis
●
No
Chapter 9
1.
Define each of the following terms:
a.
TROHOC and TROHOC fallacy
●
TROHOC is the word cohort spelled backward. Some epidemiologists
have used TROHOC as a disparaging term for case– control studies
because they believe that case– control studies are inferior to cohort
studies because they move from effect to cause rather than from cause to
effect. The TROHOC fallacy means that it is incorrect to consider the logic
of a case– control study B. to be backward because the key comparison
is identical to that of a cohort study: between exposed and unexposed
groups.
b.
Odds ratio
●
The odds ratio can be defined in two ways:
1.
the odds of being a case among the exposed compared with the
odds of being a case among the nonexposed or
2.
the odds of being exposed among the cases compared with the
odds of being exposed among the controls.
c.
Case– crossover study
●
A case– crossover study is a new variant of the case– control study that is
used to study the acute effects of transient exposures. Here, cases serve
as their own controls, and the exposure frequency during a hazard period
is compared with that during a control period.
2.
Describe the situations in which it is desirable to conduct a case– control study.
●
It is desirable to conduct a case– control study when the exposure data are
difficult or expensive to obtain, the disease is rare, the disease has long induction
and latent periods, little is known about the disease, and the underlying
population is dynamic.
3.
Suppose that a case– control study was conducted in the United States to find out
whether a Black woman’s exposure to racism during pregnancy influenced her
risk of giving birth prematurely. Investigators selected 500 cases who were
hospitalized for premature delivery and 1,000 controls. The study found that 90
case mothers and 50 control mothers reported overt incidents of racism during
their pregnancy.
a.
Set up the two-by-two table for these data.
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b.
Calculate the odds ratio.
●
Odds ratio equals ad/bc = (90 × 950)/(50 × 410) = 4.2.
c.
State in words your interpretation of this odds ratio
.
●
Black women exposed to overt incidents of racism D. during pregnancy
had 4.2 times the odds of preterm delivery compared to Black women
who did not have these experiences.
d.
Suppose that the investigators hire you as an epidemiological consultant to
help them design this study. They ask you what type of control group is
most appropriate for the study. Briefly describe the control group that you
would advise them to select, and justify your choice.
●
There are many possible answers. The basic principle is that the controls
should be comparable with the cases. They should satisfy the “would
criterion.” That is, if they had a premature delivery, they would end up as
a case E. in the study. For example, one could select women who
delivered full-term infants at the same facilities as the cases.
e.
The investigators also ask you to describe the purpose of the control group
in a case– control study. What would you tell them?
●
The purpose of the control group is to provide information on the
exposure distribution in the source population that produced the cases.
4.
Describe one advantage and one disadvantage of using population controls in a
case– control study
.
●
Advantage: They usually come from the same source population as the cases,
and therefore they are likely to be comparable.
●
Disadvantages: They are time consuming and expensive to identify, they are
usually not as cooperative as hospital controls, and their recall of prior exposures
may not be as accurate as that of cases.
5.
Describe the three strategies— survivor sampling, case– base sampling, and risk
set sampling— that investigators use to select controls.
●
In survivor sampling, the investigator selects controls from survivors who did not
become cases during the observation period. In base sampling, the investigator
selects controls from the population at risk at the start of the observation period.
In risk-set sampling, the investigator selects controls from the population at risk
as the cases are diagnosed.
6.
State the main advantages and disadvantages of case– control studies
.
●
Advantages: Case– control studies take less time and money to conduct than
cohort and experimental studies, they are well suited for studying rare diseases
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and diseases with long induction and latent periods, and they can provide
information on a large number of possible risk factors.
●
Disadvantages: The possibility of bias is increased, and it may be difficult to
establish the correct temporal relationship between the exposure and disease
because the data are retrospective.
7.
Indicate whether the following statements are true or false
:
a.
It is possible to obtain a valid estimate of disease prevalence from a typical
case– control study.
●
FALSE
b.
The purpose of a control group in a case– control study is to provide
information on the disease distribution in the source population that
produced the cases.
●
FALSE
c.
The control group in a case– control study should never include individuals
who have the case’s disease.
●
FALSE
d.
A case– control study is the most efficient design for studying the health
effects of rare exposures, whereas a cohort study is the most efficient
design for studying the risk factors for rare diseases.
●
FALSE
e.
Case identification is generally more difficult than control identification in
case– control studies.
●
FALSE
f.
The odds of illness are mathematically equivalent to the risk of illness.
●
FALSE
g.
It is preferable to use incident (that is, newly diagnosed) cases in a case–
control study.
●
FALSE
8.
Why do investigators use the odds ratio used in a case– control study (instead of
the risk or rate ratio) to measure the strength of the association between an
exposure and a disease?
●
The odds ratio is used because the numbers of exposed and unexposed
individuals needed for the risk and rate denominators are unavailable in most
case– control studies.
Chapter 17: Ethics in Research Involving Human Participants
1.
What key principle of ethical research was described in the 1947 Nuremberg
Code? Was this principle followed in the Tuskegee Syphilis Study?
●
Nuremberg Code was created after Nazi scientists were exposed conducting
experiments on concentration camp prisoners without their consent. Shortly after
10 principles were outlined, which were the first rules for experimentation
involving human subjects.
○
The first and most famous principle from this historical code states “The
voluntary consent of the human subject is absolutely essential.”
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●
U.S. Public Health began a study of the natural course of untreated syphilis
among rural Black males in Alabama. The informed consent of participants was
NOT obtained as they were not told about the study’s objective nor were they told
that they suffered from a contagious sexually transmitted disease. The
participants agreed to do the study in exchange for “free treatment”. They were
denied penicillin to cure their syphilis despite it being a commonly used drug, in
order to continue their study. Dozens of participants had died from syphilis and
many children were born with congenital syphilis.
○
study symbolizes racism in medicine and science, ethical misconduct in
research, and governmental exploitation of the vulnerable
○
this principle of informed consent was not followed in the trial
2.
Which of the following ethical principles were included in the 1964 and 1975
Declarations of Helsinki?
a.
Informed consent should be given freely.
b.
Human subjects research should be reviewed by an independent committee.
c.
The risks of participating in a study should not exceed the benefits.
d.
All of the above
3.
Describe the major principles of human subjects research identified in the 1979
Belmont Report.
●
respect for persons
○
based on the conviction that “individuals should be treated as
autonomous agents” and that “persons with diminished autonomy are
entitled to protection
●
beneficence
○
researchers must maximize the possible benefits and minimize possible
harms
■
social, physiological, legal, and financial risks and benefits must
be considered
●
justice
○
helps determine whether the burdens and benefits of research are fairly
distributed
4.
What is meant by the term informed consent ?
●
a process that involves three basic elements:
○
information exchange
○
comprehension
○
voluntariness
○
documentation
●
informed consent is an educational and decision-making process in which
potential volunteers must be effectively informed of the purpose, procedures, and
possible risks and benefits associated with the participation in a study
●
a process that goes beyond signing a form and involves meaningful discussions
between volunteers and researchers
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