What is Epidemiology?. Lilienfeld A: in Foundations of Epidemiology THE STUDY OF THE DISTRIBUTION OF A DISEASE OR A PHYSIOLOGICAL CONDITION IN HUMAN POPULATIONS AND OF THE FACTORS THAT INFLUENCE THIS DISTRIBUTION
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Lilienfeld A: in Foundations of Epidemiology
THE STUDY OF THE DISTRIBUTION OF A DISEASE OR A PHYSIOLOGICAL CONDITION IN HUMAN POPULATIONS AND OF THE FACTORS THAT INFLUENCE THIS DISTRIBUTION
(Note that epidemiology is applied to a broad variety of health related issues – not just infectious diseases.)
Identify causes and risk factors for disease.
Determine the extent of disease in the community.
Study natural history and prognosis of disease.
Evaluate preventive and therapeutic measures
Provide foundation for public policy
MEASURING DISEASE FREQUENCY IN POPULATIONS
Classifying the disease
Deciding what constitutes a case of disease in a study
Finding a source for ascertaining the cases
Defining the population at risk of disease
Defining the period of time of riskof disease
Obtaining permission to study people
Making measurements of disease frequency
Relating cases to population and time at risk
(Who? Where? When?) Examining the distribution of a disease in a population, and observing the basic features of its distribution in terms of person, place, and time.
Typical study design:
community health survey
(approximate synonyms - cross-sectional study, descriptive study)
Testing a specific hypothesis about the relationship of a disease to a putative cause, by conducting an epidemiologic study that relates the exposure of interest to the disease of interest.
Typical study designs:
THE THREE ESSENTIAL CHARACTERISTICS OF DISEASE WE LOOK FOR IN DESCRIPTIVE EPIDEMIOLOGY:
Changing or stable?
Clustered (epidemic) or evenly distributed (endemic)?
Point source or propagated.
Geographically restricted or widespread (pandemic)?
Relation to water or food supply.
Multiple clusters or one?
To undertake an analytic epidemiologic study you must first:
Know where to look
Know what to control for
Be able to formulate hypotheses compatible with laboratory evidence
THE THREE PHENOMENAASSESSED IN ANALYTIC EPIDEMIOLOGY ARE:
Microbes=Classic view – others include:
Nutrients – (ex rickets)
Physical trauma(car crashes)
Influences interaction of host and agent
Modes of communication – phenomena in the environment that bring host and agent together, such as:
Case subjects thathave the disease are
– compared to Control subjects who do not have the disease but are part of the same at-risk population. Population is not well defined as in Cohort studies
You cannot calculate attack rates because you do not know the total number of people in the community who were and were not exposed to the source of the disease under study. Without attack rates, you cannot calculate relative risk
Comparison of the two groups is quantified by an ODDS RATIO*:
*See below in notes::.
a = number of persons with disease and with exposure of interest
b = number of persons without disease, but with exposure of interest
c = number of persons with disease, but without exposure of interest
d = number of persons without disease and without exposure of interest
a+c = total number of persons with disease (“cases”)
b+d = total number of persons without disease (“controls”)
Yes No Total
25 x 18 450
EVERY HEALTH OUTCOME HAS SOME INTERESTING AND USEFUL EPIDEMIOLOGIC CHARACTERISTIC
DEATH RATES BY SOCIAL CLASS FROM A CERTAIN CAUSE AMONG 1,316 PEOPLE
WHAT CAUSE OF DEATH IS THIS?
The previous slide shows death rates by class of ticket on the Titanic, a large ocean liner that sank after colliding with an iceberg in 1912