CHAPTER 5Epidemiologic Principles and MethodsCopyrig

CHAPTER 5
Epidemiologic Principles and Methods
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Definition of Epidemiology
Epidemiology is defined as “the study of the distribution and
determinants of disease frequency in human populations.”
Step 1: Define the Disease
Death is easy to determine.
A death certificate states cause of death.
A blood test or stool culture is needed to verify a diagnosis of
certain diseases.
Some diseases are hard to define.
EMS and SARS
Sometimes a definition changes as more is learned.
AIDS
Other health outcomes include injuries and risk factors.

Disease Frequency
Count the number of people with a disease and relate that to the
population at risk (PAR).
PAR (denominator) may be the total population or exposed
population, or one gender or age group.
PAR often comes from a census.
Two ways to measure frequency are:
Incidence, the number of new cases
Prevalence, the number of existing cases
Incidence is used for studying causes of disease.
Disease Frequency (cont.)
Prevalence depends on incidence and prognosis.
If causes or risk factors increase, incidence and prevalence
increase.
If ability to diagnose increases, incidence and prevalence appear
to increase.
Prevalence rates are most useful in assessing the societal impact
of a disease and planning for healthcare services.
Mortality rates are used to measure frequency for diseases that
are often fatal.
Distribution of Disease
Who:
Sex, age, occupation, race, and economic status

When:
Looks for disease frequency over time: Season, year (long-term
trends), elapsed time since an exposure (epidemic curve)
Is crucial in tracking an outbreak of infectious diseases such as
hepatitis and legionellosis
Where:
Neighborhood (e.g., clusters), latitude (climate), urban vs. rural,
national variations
Looks at comparisons of disease frequency in different
countries, states, counties, or other geographical divisions
Determinants of Disease
Why is distribution as it is?
We can make inferences from distribution.
Epidemiologists usually speak of risk factors not causes.
Human Population
Epidemiology studies human population, usually using
observational rather than experimental methods.
Biomedical approach uses animal models to investigate the
causes of disease.
Experiments conducted on animals can yield clear answers as to
cause and effect.
For ethical reasons, experiments cannot usually be done on
humans.

Kinds of Epidemiologic Studies
Goal is to determine an association between an exposure and a
disease or other health outcome.
Studies may be prospective or retrospective.
Intervention study
Cohort study
Case-control study
Intervention Study
Epidemiologists do not perform the experiments.
Closest thing to an experiment.
Start with two groups:
Experimental group (gets the intervention or exposure)
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 (cont.)
Randomized, double-blind, placebo control is ideal.
Pharmaceutical companies conduct many clinical trials for new
drugs.
Physicians’ Health Study was a prevention study:
Aspirin to prevent heart disease
Beta carotene to prevent cancer

Field trial of polio vaccine in 1954 was randomized and double-
blind.
Kingston–Newburgh study of fluoridation to prevent tooth
decay was a community trial.
Cohort Study
Are 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 study of physicians on smoking and lung cancer
Hammond–Horn study on smoking and lung cancer in the U.S.
Case-Control Study
Faster and cheaper are the advantages.
This is the least accurate approach.
It is commonly done to follow up on a hypothesis generated by

shoeleather epidemiology.
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.
Estimate the strength of the association between exposure and
disease by calculating an odds ratio.
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.
Explain the interaction between incidence, prevalence, and
prognosis.
Give examples.
Why are the who, when, and where questions useful in
determining the causes of disease?
Give examples.

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?
Visit the National Institutes of Health website 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.
Visit the website 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?

CHAPTER 3
Powers and Responsibilities of Government
Federal Versus State
U.S. Constitution states that a fundamental purpose of the
government is “to promote the general welfare.”
Reserve clause is interpreted to mean that, since health is not
mentioned in the Constitution, responsibility for public health
primarily belongs to the states.
Interstate commerce provision justifies the activities of the
Food and Drug Administration (FDA).
Power to tax and spend is widely used by federal government to
control public health policy.
The federal government provides 65% of the funding for
Medicaid.
The New Federalism limited Congress’s powers and returned
authority to the states.
Branches of Government: Federal, State, and Local
Legislative

Legislature passes statutes.
Executive
Public health agencies carry out the law.
They may issue regulations consistent with statutes.
Judicial
Laws and regulations can be challenged in court.
Local Public Health Agencies
Local county and city health departments are often responsible
for:
Day-to-day public health tasks
Core public health functions
Providing medical care for the poor
Funding sources are variable.
City or county legislatures may not understand the importance
of core functions.
Mandates may be funded from state or federal governments.
State Health Departments
Coordinate activities of local health agencies and provide
funding
Collect and analyze data provided by the local agencies
Provide laboratory services
Manage Medicaid
License and certify medical personnel, facilities, and services
Handle environment, mental health, social services, and aging
issues, possibly through separate state agencies
Provide funding to hospitals to reimburse them for treating

uninsured patients
Federal Agencies
Department of Health and Human Services (HHS)
www.hhs.gov
Centers for Disease Control and Prevention (CDC)
www.cdc.gov
National Institutes of Health (NIH)
www.nih.gov
Food and Drug Administration (FDA)
www.fda.gov
Centers for Medicare and Medicaid Services (CMS)
www.cms.gov
Agency for Healthcare Research and Quality (AHRQ)
www.ahrq.gov
Indian Health Service
www.ihs.gov
Environmental Protection Agency (EPA)
www.epa.gov
Federal Agencies (cont.)
Occupational Safety and Health Administration (OSHA)
www.osha.gov
Department of Agriculture (USDA)
www.usda.gov
Department of Transportation
www.transportation.gov
Department of Labor

www.dol.gov
Department of Veterans Affairs
www.va.gov
Department of Defense
www.defense.gov
Department of Homeland Security
www.dhs.gov
Centers for Disease Control and Prevention
CDC is the main epidemiologic and assessment agency for the
nation.
CDC publishes Morbidity and Mortality Weekly Report
(MMWR).
CDC’s National Center for Health Statistics collects data on the
U.S. population concerning all aspects of health.
CDC also has centers to address infectious diseases, chronic
disease, injury prevention, and other issues.
National Institutes of Health
NIH is the largest biomedical research complex in the world.
Institutes exist for cancer; heart, lung, and blood; diabetes;
aging; child health and human development; and other topics.
National Library of Medicine is an NIH institute.
NIH has laboratories in Bethesda, MD and provides grant
funding to researchers at universities and research centers.
NIH has a clinical center where medical researchers test
experimental therapies.
NIH enjoys strong Congressional support.

Nongovernmental Public Health Organizations
Organizations that focus on specific diseases include:
American Cancer Society
American Heart Association
American Diabetes Association
Alzheimer’s Association
Professional membership organizations include:
American Medical Association
American Nurses Association
American Public Health Association
Organizations that play an important role in defining the future
of public health include:
National Association of City and County Health Officers
Association of State and Territorial Health Officers
Association of Schools and Programs of Public Health
Philanthropic Foundations
Rockefeller Foundation
Robert Wood Johnson Foundation
Pew Charitable Trusts
Kaiser Family Foundation
Commonwealth Fund
Bill and Melinda Gates Foundation

Choose a specific health problem.
How might federal, state, and local levels of government divide
responsibility for addressing it?
Choose a federal public health agency and visit its website.
Identify an issue that it is currently dealing with and describe
reasons for current concern.
Discuss any controversies that may be involved in actions that
the agency has taken or might need to take.
Why is it important for nongovernmental organizations to be
involved in public health activities?
Choose one of the philanthropic foundations listed on Slide 11
and visit its website to learn more about the foundation’s
activities.

CHAPTER 4
Epidemiology:
The Basic Science of Public Health
Epidemiology
Is the diagnostic discipline of public health
Is 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
Patterns of Disease Occurrence
From the following information, epidemiologists can infer why
a disease is occurring:
Who is getting the disease?
When did they get the disease?
Where is the disease occurring?
The ultimate goal is to use this knowledge to control and

prevent the spread of disease.
Epidemic Surveillance
Is a major line of defense in protecting the public against
disease
Important terms are:
Endemic versus epidemic
“Notifiable” diseases
“Shoeleather epidemiology”
System was created to control spread of known disease but also
aids in recognizing new disease.
Importance has increased with threat of bioterrorism.
John Snow and Cholera
First example of use of epidemiology to study and control a
disease was by Snow for cholera.
London had Cholera epidemics in mid-1800s.
Snow suspected an association with the water supply, the
Thames River.
He conducted a “natural experiment”:
He questioned households where cholera death had occurred.
Most deaths were associated with one water supply company.
Outbreak Investigation

Verify the diagnosis.
Construct a working case definition.
Find cases systematically.
Apply active surveillance.
Ask who, where, and when questions to describe the epidemic
by person, place, and time.
Consider the incubation period.
Look for a common source of exposure.
Epidemiology and Chronic Diseases
Identify risk factors.
Observe long-term trends.
Epidemiologic studies of chronic diseases are more complicated
and difficult than for infectious diseases or toxic contamination.
Heart disease is leading cause of death in the U.S.
Framingham Study (started in 1948)
Lung cancer and smoking studies followed in the early 1950s.
British study of physicians
Hammond–Horn study in the U.S.
Why is epidemiologic surveillance important for public health?
What role would it play if there were a bioterrorist attack?

What has epidemiology contributed to people’s understanding
of:
Heart disease?
Lung cancer?
Visit the website of The Epidemiology Monitor, a weekly
newsletter about epidemiology, and read the free news updates
available on Mondays, www.epimonitor.net.
What issues are epidemiologists concerned about this week?
Visit the website 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?
Visit the website of the Framingham Heart Study,
www.framingham.com/heart.

What are the most recent findings from this cohort study?
CHAPTER 2
Why Is Public Health Controversial?
Social Justice Versus Market Justice
Differences:
Social justice: The common good
Market justice: Individual responsibility
Questions about the scope of public health
Importance of economic factors for health
Politically controversial
Sources of Controversy
Economic impact
Individual liberty
Moral and religious opposition

Political interference with science
Economic Impact
Most public health measures have a negative economic impact
on some segment.
Businesses often resist public health measures because they
affect profits.
Those who must pay may not be the ones who benefit.
Costs may be short-term, while benefits may be long-term.
Costs are easier to calculate than benefits.
Tragedy of the Commons
Is exemplified in many environmental laws
Freedom of individuals should be restricted for the well -being
of the population.
Do laws overly restrict “freedom” to pollute?
What should be included among protected resources?
When Can Government Restrict Individual Freedom?
Restrictions to prevent harm to others is generally acceptable.
Paternalism is only acceptable for laws concerning children.
For protecting individuals from their own actions? (Libertarians
are opposed.)
Libertarian view has a strong tradition in the U.S.

Argument for restrictions for the “common good” leaves lots of
room for controversy.
Moral and Religious Opposition
Concerns:
Sex and reproduction
AIDS, STDs, teenage pregnancy, and low birth-weight babies
are major U.S. public health concerns.
Public health solutions are often viewed as promoting immoral
behavior.
Alcohol and drugs
Such opposition may discourage scientists and funding agencies
from conducting research on many important health problems.
Politics Versus Science
There is always the possibility of tension.
Conservative control of federal government intensifies the
conflict.
Under Bush administration, EPA changed a section of a major
report.
Obama administration made efforts to inform policy decisions
based on honest science.
Under Trump administration, EPA director proposal would
bring politics into initial review and synthesis of research step.

Do you agree that the philosophy of social justice is preferable
to the philosophy of market justice?
Which is likely to lead to greater improvements in public
health?
Give an example of a measure that would benefit public health
but that might be expensive to implement.
Who would benefit?
Who would pay the cost?
Give an example of a measure that would improve public health
but that might limit some people’s freedom.
Who would benefit?
Whose freedom would be limited?
How far do you believe government should go in advocating
and/or enforcing moral behavior?

CHAPTER 1
Public Health: Science, Politics, and Prevention
What Is Public Health?
C.E.A. Winslow provided the definition of public health in 1920
that is still valid today.
IOM’s The Future of Public Health refocused attention on
public health and revitalized the field.
Mission is “fulfillment of society’s interest in assuring the
conditions in which people can be healthy.”
Substance is “organized community efforts aimed at the
prevention of disease and the promotion of health.”
Core Functions of Public Health
Core functions of public health:
Assessment
Policy development
Assurance

Public Health Versus Medical Care
In medicine, the patient is the individual; in public health, the
patient is the community.
Public health diagnoses the health of the community using
public health sciences.
Treatment of a community involves new policies and
interventions.
Goal of medicine is to cure; goal of public health is to prevent
disease and disability.
Less than 3% of the nation’s total health spending is devoted to
public health.
Life expectancy of Americans has increased by 30 years over
the 20th century, and only 5 of the 30 years are attributed to
modern medicine.
Public Health: Science and Politics
Science is how we understand threats to health, determine what
interventions might work, and evaluate whether the
interventions worked.
Politics is how we as a society make decisions about what
policies to implement.
Politics is part of both the policy development and assurance
functions of public health.
Community pays for public health initiatives through taxes.

Public Health Disciplines
Epidemiology
Statistics
Biomedical Sciences
Environmental Health Science
Social and Behavioral Sciences
Health Policy and Management
Epidemiology
Epidemiology is the basic science of public health.
The study of epidemics:
Focuses on human populations, usually starting with an
outbreak of disease in a community
Looks for common exposures, seeking the causative factor
Deciphers causes of new disease and prevents spread of old,
well-understood diseases
Epidemiologists are mainstays of local public health
departments.
“Shoe-leather epidemiology”
Statistics
Governments collect health data on the population.
These numbers are diagnostic tools for the health of the
community.
The science of statistics is used to calculate risks and benefits.

Statistical analysis is an integral part of any epidemiological
study seeking the cause of a disease.
Statistical analysis is an integral part of any clinical study
testing the effectiveness of a new drug.
Biomedical Sciences
A major portion of human disease is caused by microorganisms.
Control of infectious diseases was a major public health focus
in the 19th and early 20th centuries.
Biomedical research remains important to understanding and
control of new diseases and noninfectious diseases.
Chronic diseases
Genetics
Environmental Health Science
A classic component of public health:
Much of the public health improvement in the U.S. in the 20th
century was due to improved environmental health.
Health is affected by exposure to environmental factors:
Air quality
Water quality
Solid and hazardous wastes
Safe food and drugs
Global environmental change
Thousands of new chemicals enter the environment every year,
and little is known about their effect on human health.

Social and Behavioral Sciences
Behavior is now the leading concern of factors that affect
people’s health.
A theory of health behavior is that social environment affects
people’s behavior.
Major health threats are tobacco, poor diet, and physical
inactivity and injuries.
Blacks have a lower overall life expectancy than whites even
when incomes are similar.
Other ethnic minority groups are also at increased risk for a
variety of health problems.
Health Policy and Management or Health Administration
This area of study examines the role of medical care in public
health.
Cost of medical care in the U.S. is out of control.
U.S. has a high percentage of population without health
insurance.
These people often lack access to medical care.
Quality of medical care can be measured and is often
questionable.
Medical care has eaten up profits that could be used more
beneficially for education, housing, and the environment.

Public Health: Prevention and Intervention
Primary prevention prevents an illness or injury from occurring
at all.
Secondary prevention minimizes the severity of the disease or
injury once it has occurred.
Tertiary prevention minimizes disability by providing medical
care and rehabilitation services.
Public Health Approach
Define the health problem.
Identify risk factors associated with the problem.
Develop and test community-level interventions to control or
prevent the cause of the problem.
Implement interventions to improve the health of the
population.
Monitor interventions to assess their effectiveness.
Chain of Causation
Chain of Causation involves:
Agent
Host
Environment
This is a traditional approach to dealing with infectious
diseases.
Interventions can focus on any of these targets.
This model can also be used for other kinds of illnesses or

injuries.
Public Health and Terrorism
Events of 9/11 and the anthrax letters highlighted the
importance of public health.
Public health response to disasters, natural and man-made, helps
to control the damage and to prevent further harm to survivors
and rescuers.
Public health response to 9/11 was essentially the same as
needed for other disasters, such as factory explosions and plane
crashes.
Bioterrorism is recognized primarily through classic public
health measures similar to those used for natural epidemics.
The threat of bioterrorism did more to teach the public about
public health than any educational program.
Describe actions that governments have taken to ensure that
people are safer and healthier today than people were 100 years
ago.
Discussion Questions 2
What are the three core functions of public health?
How do these functions compare with the functions of medical

care?
How are the six disciplines of public health used to accomplish
the core functions?
Identify a health problem in your community.
What are some risk factors associated with the problem?
Suggest a possible intervention that the community could take
to ameliorate the problem.
Visit the website for American Public Health Association
(APHA), www.apha.org.
Read the highlights from the current issue of the American
Journal of Public Health.
Which of the public health sciences does each of these articles
belong to?
Visit the website for The Nation’s Health, the official
newspaper of APHA, thenationshealth.aphapublications.org/.
Read the headlines of the current issue to get an idea of the
range of topics encompassed by the field of public health.

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