 
Epidemiology
Self Study Module
Rojann R. Alpers, Ph.D., R.N.
Overview This module discusses and provides opportunity to apply the basic concepts
and principles of epidemiology.
Module Objectives:
1. Define Epidemiology
2. Discuss the major epidemiological concepts
3. Discriminate between the major types of epidemiological research
studies:
A) Retrospectives;
B) Prospective;
C) Cross-Sectional; and
D) Experimental
4. Apply and utilize epidemiology with selected public health
issues
Objective 1.
Epidemiology: is the study of the DISTRIBUTION and DETERMINANTS (causes) of
HEALTH, INJURIES & DISEASE in a human
population. It is also:
A conceptual framework
A discipline
A specialized research methodology
Where does the word Epidemiology come from?
Answer
What word is used to describe unusual occurrence?
Answer
What word is used to describe "regional epidemics?"
Answer
Identify at least four ways in which Epidemiology helps us:
Answer
Objective 2.
When preparing to conduct an epidemiological exploration data is
collected about both DISTRIBUTION and DETERMINANTS of health, illness and/or injury.
Important information to collect when attempting to understand DISTRIBUTION.
1. TIME - date, season, year
2. PLACE - country, urban, rural
3. PERSONAL ATTRIBUTES - age, gender,
race/ethnicity
4. SUPPLEMENTAL DATA - educational status,
occupation, income level
5. NEIGHBORHOOD INFORMATION - insects, pets,
rodents, plants, EMF, geologic features
6. DIETARY HABITS - home, restaurants.
Important information to collect when attempting to understand DETERMINANTS. Determinant factors are typically divided into the
TRIAD of epidemiology:
Host Factors (ALWAYS in reference to humans and which make the human susceptible
to the agent (causative factors):
1. GENETICS - weakened/absent/aberrant genes,
race/ethnicity
2. PHYSIOLOGIC - age pregnancy, puberty,
immunity/resistance, gender, impaired bodily functions, pre-existing disease or inter-current
disease, hypersensitivity
3. PSYCHIC - stress, developmental level, spiritual
intactness
4. BEHAVIORAL - nutrition, rest, occupation, personal
hygiene, food handling, excrement disposal, personal contacts, recreation
Agent Factors (refer to the "factors" without which the disease/injury or healthful event
cannot occur. This could refer to a SUBSTANCE (living
or inanimate) or a FORCE (lack of or excessive
presence) which is the immediate or proximal CAUSE
of the situation/event.
1. NUTRITIVE ELEMENTS - fats, carbohydrates, lack
of amino acids, minerals, waters
2. EXOGENOUS CHEMICALS - poisons, irritants,
inhalants, smoke, pesticides, medications, sunlight, poison ivy.
3. ENDOGENOUS CHEMICALS - out-of-balance
bodily functions (impaired kidney leads to uremic acit build-up orbilirubin leads to jaundice
or lipids lead to cholersterol), over/under secretion of hormones
4. PHYSIOLOGIC FACTORS - loss of elasticity of lens
(leads to visual "diseases"), narrowing of blood vessels (leads to CV and CBV disease)
5. PHYSICAL FACTORS - atmospheric changes (the
bends), EMF/x-rays, radon
6. PARASITES - bacteria, protozoa, spores, amoebę,
scabies, lice
7. PSYCHOLOGICAL - self-esteem, locus of control,
stress, self efficacy, coping strategies, etc.
Definitions related to AGENTS:
1. VIABILITY - the ability to survive and withstand
adverse environmental influences such as heat,
cold, dryness, moistness, radiation
2. VULNERABILITY - the degree to which
chemotherapeutic and antibiotic substances shorten the period
of infectivity and transmission
3. INFECTIVITY - being able to lodge and multiply in a
host. How much of an agent does it require
to "infect."
4. PATHOGENICITY - the ability of an agent to induce
disease
5. VIRULENCE - the ability of an agent to induce
SEVERE disease or death
Environmental Factors (embraces ALL that is external to the host and agent):
1. GEOLOGIC - soil, radon, water, climate,
pollution
2. BIOLOGIC - plants, animals, parasites, animal
dandruff, plant juices, insects, rodents
3. SOCIOECONOMIC - availability of natural resources,
socio-political climate, population distribution,
housing, educational status
Epidemiology looks at a triad of
factors:
Objective 3.
Types of Epidemiological Studies
1. Retrospective Studies/Case Studies: These involved looking BACKWARDS from the effects
to preceding causes. This approach requires (2) groups which
have both been exposed to a disease for comparison. The
study group is the group that following exposure became symptomatic.
The control group was the group that did
not become symptomatic/ill from the exposure.
How does this type of study help us understand a healthful / illness/ injury
phenomenon?
Answer
2. Prospective Studies/Cohort Studies: This type of study requires (2) groups, one of which was exposed
to the disease and one who was not
exposed to the disease. The two groups are then compared.
How does this type of study help us undertand a healthful / illness/ injury
phenomenon?
Answer
3. Experimental Studies: There are usually (2) or more
groups of participants who ideally are randomly assigned to either the control of experimental /intervention
groups. The investigator controls the exposure - nonexposure.
How does this type of study help us understand a healthful / illness / injury
phenomenon?
Answer
What might be some of the ethical concerns an experimental study would elicit?
Answer
4. Cross Sectional Studies / Survey Studies: This is often referred to as a "fishing expedition." Measurements / tests of a variety of phenomenon are taken at the same time. These studies are frequently made with large populations. A random sample is used and a large amount of data is collected (distribution and determinant). A battery of physical and/or psychological tests are given. Then the data is correlated. (i.e. Do nurses have a greater prevalence of hypertension than the lay public? OR Do fireman have a greater prevalence of migraine headaches than other groups of people?)
How does this type of study help us understand a healthful/injury/illness phenomenon?
Answer
5. Analytic Studies / Statistical Studies: This type of study's main purpose is to look for ASSOCIATIONS and not really cause-effect relationships -- or previously discovered to suspected associations / relationships. However, if we have:
-- time sequence (the assumed cause CLEARLY precedes the effects);
-- STRONG association between variables (the frequency of effects increases as the cause increases) and
-- the association is CONSISTENT with the existing knowledge base -- these studies (over a period of wime and with replication) often take on the appearance of "cause-effect" research.
Give an example of correlational (associative) research that has now become viewed as cause/effect research?
Answer
6. Descriptive Studies: This type of study simply seeks to describe health/disease conditions. Data collected includes:
1. Time in which the persons were found affected (year, season, day).
2. Place in which the persons were found affected (country, state, urban/rural community).
3. Characteristics of the persons found affected (age, gender, ethnicity, occupation, education, SES, marital status, family history).
REMEMBER: There is an aspect of descriptive studies in ALL epidemiological research (or should be!)
How does this type of study help us understand a healthful / injury / illness phenomenon?
Answer
Objective 4.
Choose one of the following community health issues and construct an epidemiological
triad.
To receive credit for completing this exercise, please
complete the following:
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