2. • Epidemiology uses strong sampling methods and
study designs to test refutable hypotheses regarding
the causes of important health, mental health, and
social outcomes
• Epidemiologic studies often use population-based
samples to measure causal risk factors prior to the
onset of the disorder to strengthen causal inferences
3. • epidemiology searches for patterns by examining characteristics of
person, place, & time. These characteristics are carefully
considered when a disease outbreak occurs, because they provide
important clues regarding the source of the outbreak.
1:Person
• Information about the cases is typically recorded in a "line listing,"
a grid on which information for each case is summarized with a
separate column for each variable. Demographic information is
always relevant, e.g., age, sex, and address, because they are often
the characteristics most strongly related to exposure and to the risk
of disease.
4. 2:Place
Assessment of an outbreak by place provides information on
the geographic extent of a problem and may also show
clusters or patterns that provide clues to the identity and
origins of the problem.
3:Time
When investigating the source of an outbreak of infectious
disease, Investigators record the date of onset of disease for
each of the victims and then plot the onset of new cases over
time to create what is referred to as an epidemic curve.
5. • After interviewing affected individuals,gathering data to characterize
the outbreak by time, place, and person, and consulting with other
health officials,
• A disease detective will have more focused hypotheses about the
source of the disease, its mode of transmission, and the exposures
which cause the disease. Hypotheses should be stated in a manner
that can be tested.
• Hypotheses about the determinants of disease arise from considering
the characteristics of person, place, and time and looking for
differences, similarities, and correlations. Consider the following
examples:
6. • 1:Differences:
• if the frequency of disease differs in two
circumstances, it may be caused by a factor that
differs between the two circumstances.
For example, there was a substantial difference in the
incidence of stomach cancer in Japan & the US. There
are also substantial differences in genetics and diet.
Perhaps these factors are related to stomach cancer.
7. 2: SIMILARITIES:
if a high frequency of disease is found in several
different circumstances & one can identify a common
factor, then the common factor may be responsible.
Example: AIDS in IV drug users, recipients of
transfusions, & hemophiliacs suggests the possibility
that HIV can be transmitted via blood or blood
products.
8. 3: CORRELATIONS:
If the frequency of disease varies in relation to some factor,
then that factor may be a cause of the disease.
Example: differences in coronary heart disease vary with
cigarettes consumption.
9. Evaluation:
• There are two approaches to evaluating hypotheses: comparison of the
hypotheses with the established facts and analytic epidemiology, which allows
testing hypotheses.
• A comparison with established facts is useful when the evidence is so strong that
the hypothesis does not need to be tested. A 1991 investigation of an outbreak of
vitamin D intoxication in Massachusetts is a good example.
• All of the people affected drank milk delivered to their homes by a local dairy.
Investigators hypothesized that the dairy was the source, and the milk was the
vehicle of excess vitamin D. When they visited the dairy, they quickly recognized
that far more than the recommended dose of vitamin D was inadvertently being
adding to the milk. No further analysis was necessary.
10. • Analytic epidemiology, is used when the cause is less clear.
Hypotheses are tested, using a comparison group to quantify
relationships between various exposures and disease. Case-control,
occasionally cohort studies, are useful for this purpose
11. Reference:
1. Costello EJ, Compton SN, Keeler G, Angold A. Relationships between
poverty and psychopathology: A natural experiment. JAMA.
2003;290:2023–2029
