Introduction To EpidemiologyIntroduction To Epidemiology

Muhammad Rehan Muhammad Rehan

What is Epidemiology?What is Epidemiology?

Two Definitions of an EpidemicTwo Definitions of an Epidemic

Last JM: A Dictionary of Epidemiology. 4th ed

THE OCCURRENCE IN A COMMUNITY OR REGION OF CASES

OF AN ILLNESS, SPECIFIC HEALTH-RELATED BEHAVIOUR, OR OTHER HEALTH-RELATED EVENTS CLEARLY IN EXCESS OF NORMAL EXPECTANCY.

From the Babylonian Talmud (Tractate Taanit, 21A)

A CITY THAT HAS FIFTEEN HUNDRED MILITARY AGE MEN SUCH AS AKKO, AND THAT SUFFERS NINE DEATHS IN THREE DAYS, THAT IS CONSIDERED A PLAGUE. A CITY WITH FIVE HUNDRED SUCH AS AMIKO, AND HAS THREE DEATHS IN THREE DAYS, THAT IS CONSIDERED A PLAGUE.

Definitions of Epidemiology Definitions of Epidemiology

Oxford English Dictionary

THE BRANCH OF MEDICAL SCIENCE WHICH TREATS OF EPIDEMICS

Kuller LH: Am J Epid 1991;134:1051Kuller LH: Am J Epid 1991;134:1051

EPIDEMIOLOGY IS THE STUDY OF "EPIDEMICS" AND THEIR PREVENTION

Anderson G,quoted in Rothman KJ: Modern Epidemiology

THE STUDY OF THE OCCURRENCE OF ILLNESS

EPIDEMIOLOGYEPIDEMIOLOGY

� Definition: Epidemiology is the basic science of community medicine that pertains to the study of the (I) Distribution (ii) Dynamics (iii) Determinants of diseases (D.D.D). A recent definition agreed upon by an A recent definition agreed upon by an international panel is the following

� “Epidemiology is the study of distribution and determinants of health related states and events in specified population and the application of the study to the control of health problem.”

Definitions of EpidemiologyDefinitions of 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 DISTRIBUTIONTHIS DISTRIBUTION

Last JM: A Dictionary of Epidemiology

THE STUDY OF THE DISTRIBUTION AND DETERMINANTS OF HEALTH RELATED STATES AND EVENTS IN POPULATIONS AND THE APPLICATION OF THIS STUDY TO CONTROL OF HEALTH PROBLEMS“

What Is The Unique Skill What Is The Unique Skill Of Epidemiologists?Of Epidemiologists?

MEASURING DISEASE

FREQUENCY IN FREQUENCY IN POPULATIONS

Measuring Disease Frequency Measuring Disease Frequency Has Several ComponentsHas Several Components

� Classifying and categorizing disease

� Deciding what constitutes a case of disease in a study

� Defining the period of time of risk of disease

� Obtaining permission to study peopleconstitutes a case of

disease in a study

�

� Finding a source for ascertaining the cases

� Defining the population at risk of disease

study people

� Making measurements of disease frequency

� Relating cases to population and time at risk

Two Broad Types of Two Broad Types of EpidemiologyEpidemiology

Examining the distribution of a

disease in a population, and observing the basic features of its

Testing a specific hypothesis

about the relationship of a disease to a putative cause, by

DESCRIPTIVE EPIDEMIOLOGY ANALYTIC EPIDEMIOLOGY

observing the basic features of its distribution in terms of time, place, and person.

Typical study design:

community health survey(approximate synonyms - cross-sectional study, descriptive study)

disease to a putative cause, by conducting an epidemiologic study that relates the exposure of interest to the disease of interest.

Typical study designs: cohort, case-control

Epidemiologists are required to have some knowledge of the disciplines of public health, clinical medicine, pathophysiology, statistics, and the social sciences.

• public health, because of the emphasis on disease prevention.

• clinical medicine, because of the emphasis on disease classification and diagnosis.

• pathophysiology, because of the need to understand basic biological mechanisms in disease.

• statistics, because of the need to quantify disease frequency and its relationships to antecedents.

• social sciences, because of the need to understand the social context in which disease occurs and presents.

Purposes Of EpidemiologyPurposes Of Epidemiology(Gordis: Epidemiology, p. 3(Gordis: Epidemiology, p. 3--4)4)

1. Identify causes and risk factors for disease.

2. Determine the extent of disease in the community.

3. Study natural history and prognosis of 3. Study natural history and prognosis of disease.

4. Evaluate preventive and therapeutic measures

5. Provide foundation for public policy

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