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Solved by verified expert:How It WorksHow Epidemiology worksOutbreak of HepatitisLegionnaires DiseaseEosinophilia-Myalgia SyndromeHeart DiseasesLung cancer Explain briefly the following EpidemiologyIntervention StudiesCohort StudiesCase-Control Studies Explain briefly the following Problems with studying HumansSources of ErrorEthics in epidemiologyConflicts of interest in Drug Trials
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Chapter 6
Problems and Limits of Epidemiology
Problems with Studying Humans
• Intervention study: subjects may not follow
prescribed behavior throughout study period
• Cohort study: sometimes hard to isolate which of
many factors are responsible for health differences
• Case-control study: control group may not be
truly comparable; also errors in reporting or recall
• For all studies, must worry about differential dropouts
Sources of Error
• Random variation
• Confounding variables
• Bias
– Selection bias
– Reporting bias or recall bias
Factors that Lend Validity to
Results
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Strong association
Dose-response relationship
Known biological explanation
Large study population
Consistent results from several studies
Hormone Replacement Therapy
• Conflicting results from two major studies
• Clinical trial is the gold standard
• Results of cohort study were confounded by
associated factors that made women taking
HRT healthier, even without the therapy
Ethical Issues
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Nazi experiments on humans
Tuskegee syphilis study
New rules – informed consent
New rules — institutional review boards
Importance of clinical trials
Possibility of conflict of interest by medical
providers who stand to profit
Conflicts of Interest in Drug
Trials
• Drug companies are required to conduct
randomized controlled trials on any new drug
before it can be approved
• Harmful side effects have frequently become
obvious after drugs were approved
• There is evidence that drug companies sometimes
suppress negative findings
• All clinical trials must now be registered in
advance in a public database
Discussion Question 1
• What are the strengths and weaknesses of
each of the major types of epidemiologic
study: randomized controlled trial, cohort,
and case-control?
Discussion Question 2
• Have you heard of the Tuskegee Syphilis
Study? Why was it unethical? What
influence has it had on the conduct of
clinical trials?
Discussion Question 3
• Visit the Web site of the Hastings Center
(www.thehastingscenter.org)
• What issues is the Hastings Center
concerned with this month?
Chapter 4
Epidemiology: The Basic Science of
Public Health
Epidemiology
• The diagnostic discipline of public health
• A major part of public health’s assessment
function
• Investigates causes of diseases
• Identifies trends in disease occurrence
• Evaluates effectiveness of medical and
public health interventions
• An observational science
Patterns of Disease Occurrence
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•
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Who is getting the disease?
When did they get the disease?
Where is the disease occurring?
From this information, epidemiologists can
infer why the disease is occurring.
Epidemic Surveillance
•
•
•
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Endemic vs. Epidemic
Notifiable diseases
Recognition of new disease
Increased importance with threat of
bioterrorism
John Snow and Cholera
• Cholera epidemics in London, mid 1850s
• Suspected an association with water supply,
which came from the Thames River
• “Natural experiment”
• Questioned households where a cholera
death had occurred
• Most deaths associated with one company
Outbreak Investigation
• Verify the diagnosis
• Construct a working case definition
• Find cases systematically – active
surveillance
• Ask the who, where, and when questions to
describe the epidemic by person, place, and
time. Consider the incubation period
• Look for common source of exposure
Epidemiology and Chronic
Diseases
• Identify risk factors
• Observe long-term trends
• Heart disease – leading cause of death in
U.S.
– Framingham Study – started in 1948
• Lung cancer and smoking – early 1950s
– British Physicians’ Study
– Hammond-Horn study in U.S.
Discussion Question 1
• Why is epidemiologic surveillance
important for public health? What role
would it play if there were a bioterrorist
attack?
Discussion Question 2
• What has epidemiology contributed to
people’s understanding of:
– Heart disease?
– Lung cancer?
Discussion Question 3
• Visit the Web site of the EpiMonitor, the
weekly newsletter of epidemiology, and
read the free news updates available on
Mondays (www.epimonitor.net)
• What issues are epidemiologists concerned
about this week?
Discussion Question 4
• Visit the Web site of CDC’s Morbidity and
Mortality Weekly Report,
(www.cdc.gov/mmwr)
• Has the CDC reported any new outbreaks or
health risks this week? What other issues is
the nation’s epidemiology agency
concerned about this week?
Discussion Question 5
• Visit the Web site of the Framingham Heart
Study, (www.framingham.com/heart)
• What are the most recent findings from this
cohort study?
Chapter 5
Epidemiologic Principles and
Methods
Definition of Epidemiology
• Epidemiology is the study of the
distribution and determinants of disease
frequency in human populations
Step 1: Define the Disease
• Death is easy to determine – death certificates
have cause of death
• Some diseases need blood tests or stool cultures to
verify diagnosis
• Some diseases are hard to define – e.g. EMS,
SARS
• Sometimes definition changes as more is learned –
e.g. AIDS
• Other health outcomes – injuries, risk factors
Disease Frequency
• Count number of people with disease and relate to
the population at risk (PAR)
• PAR (denominator) may be total population or
exposed population, or one gender or age group;
often comes from census
• Two ways to measure frequency:
– Incidence – number of new cases
– Prevalence – number of existing cases
• Incidence is used for studying causes of disease
Disease Frequency, ctd.
• If causes or risk factors increase, incidence
and prevalence increase
• If ability to diagnose increases, incidence
and prevalence increase
• Prevalence depends on incidence and
prognosis
Distribution of Disease
• Who – sex, age, occupation, race
• When – season, year (long-term trends),
elapsed time since an exposure (epidemic
curve)
• Where – neighborhood (e.g. clusters),
latitude (climate), urban vs. rural, national
variations
Determinants of Disease
• Why is distribution as it is?
• Can make inferences from distribution
• Risk factors
Human Population
• Epidemiology observes humans, in contrast
to biomedical sciences, which can do
experiments on laboratory animals
Kinds of Epidemiologic Studies
• Goal is to determine an association between
an exposure and a disease or other health
outcome
• May be prospective or retrospective
• Intervention study
• Cohort study
• Case-control study
Intervention Study
• Closest thing to an experiment
• Start with two groups: experimental group (gets
the intervention or exposure) and control group
• Watch them over time and compare outcomes
• Experimenter chooses who is in which group
• Two groups should be as similar as possible so
that intervention is the only difference
Intervention Study, ctd.
• Randomized, double-blind, placebo control is the ideal
• Pharmaceutical companies conduct many clinical trials
for new drugs
• Physicians’ Health Study – prevention study
– Aspirin to prevent heart disease
– Beta carotene to prevent cancer
• Field trial of polio vaccine – 1954
• Kingston-Newburgh study of fluoridation to prevent
tooth decay
Cohort Study
• For situations when doing an intervention
study would be unethical or too difficult
• Considered the next most accurate
• Choose a large number of healthy people,
collect data on their exposures, and track
outcomes over time
• The only difference from intervention is that
people choose their own exposures
Cohort Study — examples
• Framingham Heart Study
• Nurses’ Health Study
• British physicians study on smoking and
lung cancer
• Hammond-Horn study on smoking and lung
cancer in U.S.
Case-Control Study
• Choose people who already have disease
• Choose a healthy control group of
individuals as similar as possible to cases
• Interview them all and ask for their previous
exposures
• Advantage: faster and cheaper
• Least accurate approach
Discussion Question 1
• What is the difference between incidence
and prevalence? Why is incidence more
useful in identifying the cause of a disease?
When is it most useful to use prevalence?
Give examples for each.
Discussion Question 2
• Explain the interaction between incidence,
prevalence, and prognosis. Give examples.
Discussion Question 3
• Why are the who, when, and where
questions useful in determining the causes
of disease? Give examples.
Discussion Question 4
• Explain the three major types of
epidemiologic studies.
• Which is most likely to yield a valid result?
Why?
• Which is likely to yield an answer in the
shortest period of time? Why?
Discussion Question 5
• Visit the National Institutes of Health Web site on
clinical trials (www.clinicaltrials.gov). Browse by
condition
• How many clinical trials are going on right now?
• Choose a condition and investigate what
treatments are being tested for that condition.
Discussion Question 6
• Visit the Web site of the Nurses’ Health
Study (www.channing.harvard.edu/nhs)
• Read the most recent annual newsletter.
What are the most recent findings of this
cohort study?
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