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2. "I keep six honest serving men;they taught me all I knowTheir names are what, why , when, how , where, and who" 3. ETYMOLOGY

  • The term epidemiology is derived from three Greek words'epi'means among or upon'demos'meaningpeople and ' logos'means study or knowledge.


  • the branch of medical science dealing with epidemics(Parkin in 1873)
  • Epidemiolgy is the science of mass phenomena of infectious diseases.(FROST, 1927)
  • Epidemiology is the study of disease, any disease, as a mass phenomenon.(GREENWOOD , 1934)


  • The study of the distribution and determinants of disease frequency in man .(MacMahan , 1960)
  • Epidemiology is the study of various factors and conditions that determine the occurrence and distribution of health . disease, defect, disability , and death among groups of individuals.
  • (Clark, 1965)


  • the study of the distribution and determinants of health related states and events in specific populations and the application of the study of control health problems"
  • (John.M.Last 1988).

7. History Of Epidemiology

  • Epidemiology begins with Adam and Eve , both trying to investigate the qualities of the "forbidden fruit".
  • The first epidemiologist that emerged on the scene was Hippocrates himself.(460-447 BC).

8. History Of Epidemiology

  • The most outstanding epidemiological study in the nineteenth century was that conducted by john Snow on cholera in London in the year 1854 in which he established, beyond any doubt, that cholera is a water-borne disease.

9. History Of Epidemiology

  • The application of epidemiology in nursing can be traced back to Florence Nightingale, considered the issues related to the hospital statistics and diseases classification and took suggestions from William Farr, the chief statistician, General Registar Office,England. Florence Nightingale contributed to the development of epidemiology in her work with British soldiers during the Crimean War (1854 to 1856)

10. History Of Epidemiology

  • Recently, epidemiological studies were instrumental in exploring the natural history of AIDS,identifying modifiable risk factors associated with it and providing a framework for its control at a time when neither a vaccine nor an effective treatment is available.


  • agent
  • host
  • environment

agent host environment 12. BASIC CONCEPTS IN EPIDEMIOLOGY

  • Agent:an animate or inanimate factor that must be present or lacking for a disease or condition to develop.
  • Host:a living species (human or animal) capable of being infected or affected by an agent.
  • Environment : all that is internal or external to a given host or agent and that is influenced and influences the host and/or agent.

13. Scope Of Epidemiology

  • Scope :Scope means opportunity for unhampered motion, activity , or thought, orextend of appications.

14. Scope Of Epidemiology

  • Epidemiology studies the determinants of health-related states and events.
  • Epidemiology studies the distribution of health-related states and events; the distribution is viewed in three epidemiological dimensions of time, place and person.

15. Scope Of Epidemiology

  • Epidemiology finds application in the control of health problems.
  • Modern epidemiology deals with measurements of occurrence of health related states or events which include diseases, disabilities, death, physiological conditions, health needs, health demands, health care utilization and health behaviors.

16. Scope Of Epidemiology

  • Evaluation of usefulness and effectiveness of new or innovative techniques.
  • Conducting epidemiological researches on changing trends in the distribution and determinants of health and illness.


  • Aim:The word aim means todirect towards an intented target


  • According to International Epidemiological Association(IEA), epidemiology has three main aims,
  • To describe the distribution and magnitude of health and disease problems in human populaions.
  • To identify the etiological factors or risk factors in the pathogenicity of disease.
  • To provide the data essential to the planning , implementation and evaluation of services.


  • to study the occurrence of diseases in a population.
  • to study historically the rise and fall of disease in the population.
  • to identifyhealth problems in a community.
  • quantifying a health problems in the community


  • quantifying a health problems in the community
  • to diagnose the health of the community
  • Searching for cause and risk factors
  • to identify determinants of disease


  • to estimate individual risks and chances
  • to plan health services
  • toevaluate intervention measures
  • to complete Natural History of Diseases.
  • to identify syndrome.
  • to forecast future disease trends.

22. Ultimate Aim Of Epidemiology eliminate or reduce the health problemor its consequencespromote the healthand well being ofsociety as a whole. 23. METHODS OF EPIDEMIOLOGY

  • Method is defined as a mean or manner of procedure, especially a regular and systematic way of accomplishing something.

24. Classification Of Epidemiological Studies

  • 1) Observational epidemiology
  • Descriptive epidemiology
  • Analytical epidemiology
  • ecological studies
  • cross-sectional studies
  • case control studies
  • cohort studies
  • 2)Experimental Or Investigative Epidemiology
  • Randomized controlled trial
  • Field trial
  • Community trial

25. 1) Observational epidemiology

  • Theobservational studies collect evidences based on the observations of routine records , reports, and routine happenings. Under observational epidemiology , an epidemiologists measures the incidence and prevalence of disease, death, defect or disability or any other event in the community orpopulation and does not intervene. Observational epidemiology falls into descriptive epidemiology and analytical epidemiology.

26. Descriptive Epidemiology

  • Descriptive epidemiology refers to the distribution of disease, death, and other health outcomes in the population according to person, place, and time. This type of epidemiology provides a picture of how things are or have been the who, where, and when of disease patterns.
  • Descriptive studies are usually the first phase of an epidemiological investigation.
  • These studies are concerned with observing the distribution or disease, or health related characteristics in human .populations and identifying characteristics with which the disease seems to be associated

27. Procedures in descriptive Studies

  • Defining the population to be studied
  • Defining the disease under study
  • Describing the disease by
    • Time
    • place
    • person
  • Measurement of disease .
  • Comparing with known indices .
  • Formulation of an etiological hypothesis .

28. Defining the population to be studied

  • Criteriafor defininga population
  • The "defined population" can be the whole population in a geographic area, or more often are representative sample taken from it. The defined population can also be a specially selected group such as age and sex groups, occupational groups, hospital patients, school children, small communities as well as wider groupings

29. Defining the population to be studied

  • The defined population needs to be large enough so that age, sex and other specific rates are meaningful.
  • The community chosen should be stable without migration into or out of the area.
  • It should be clear who does and who does not belong to the population as for example, visitors and relations.
  • The most essential ingredient is community participation.. Furthermore, the population should not be overtly different from other communities in the region.
  • Finally, a health facility should be close enough to provide relatively easy access for patients requiring medical services.


  • The , epidemiologist looks out for an "operational definition", i.e..a definition by which the disease or condition can be identified and measured in the defined population with a degree of accuracy.


  • The primary objective of descriptive epidemiology is to describe the occurrence and distribution of disease (or health- related eve