Methods of Epidemiology - Descriptive epidemiology
- 1. DESCRIPTIVE EPIDEMIOLOGY Prepared by: Krupa Mathew. M, Assistant Professor
- 2. INTRODUCTION The Greek physician Hippocrates is sometimes said to be the father of epidemiology. He is the first person known to have examined the relationships between the occurrence of disease and environmental influences. The word epidemiology is derived from Greek terms- “epi”-upon, among, “demos” –people, district, “logos” –study, word, discourse. Epidemiology literally is the study of something that affects population.
- 3. METHODS OF EPIDEMIOLOGY Epidemiology Observational Descriptive Analytical Ecological Cross sectional Case control Cohort Experimental RCT Field trial Community trial
- 4. Descriptive Epidemiology • Descriptive study is the first phase of epidemiological investigation. • Observing the distribution of disease or health related events in human population. • Identify the characteristics with which the disease is associated. • Basically 3 questions are asked who, when and where. • Who means the person affected, where means the place and when is the time distribution
- 5. Descriptive Epidemiology Studies concerned with observing the distribution of dise ase or health-related characteristics. The steps in descriptive epidemiology are •Defining the population to be studied •Defining the disease under study •Describing the disease by time, place and person •Measurement of disease •Comparison with known indices •Formulation of an etiological hypothesis
- 6. Defining the population • The defined population can be the whole population in a geographic area or more often representative sample taken from it. • Not only the total number, but also its composition in terms of age, sex, occupation, cultural characters etc. • The community chosen should be stable, without migration into or out of the area. Defined under • Age and sex composition of selected group. • Education • Occupation • Socio-economic status • Marital status
- 7. Defining the disease The disease is defined in such away that helps in identifying and measuring the disease in the defined way with a degree of accuracy. “Operational Definition” : by which the disease or condition can be identified and measured in the defined population with a degree of accuracy. If definition is not valid, it can be powerful source of error in presentation and comparability of measurements. Case definition should be adhered to throughout the study.
- 8. Describing the disease The occurrence and distribution of disease is described by time, place, and person and identifying those characteristics associated with presence or absence of disease in individuals.
- 9. TIME Short term fluctuations Common source epidemics single exposure or point source epidemics continuous or multiple source epidemics Propagated epidemics Periodic fluctuations Seasonal trend Cyclical trend Long term or secular trends
- 12. Measurement of Disease • “Disease load” • The measurement of disease is done in terms of mortality and morbidity indicators. • The morbidity can be expressed in terms of two units- “incidence” and “prevalence”. • Descriptive Epidemiology either uses a cross- sectional or longitudinal study. A. Cross-sectional Studies : are also called as “prevalence studies” as they measures the prevalence of disease. - examination at a point in time, so that results can be projected to the whole population. -More useful for chronic than short lived diseases. B. Longitudinal Studies : Observations are repeated in the same population over a long period of time. They are extremely useful : 1. For studying the natural history of the disease and its outcome. 2. For identifying the risk factors associated with the disease 3. For calculating the incidence rate of the disease.
- 13. COMPARING WITH KNOWN INDICES The essence of epidemiology is make comparisons and ask questions. - to arrive at clues to disease etiology. - also helps in defining the groups who are at increased risk for certain diseases.
- 14. FORMULATION OF HYPOTHESIS A hypothesis is a supposition, arrived from observation and reflection. -Using the techniques of descriptive epidemiology, it is possible to formulate hypothesis relating to disease etiology. -It can be accepted or rejected using the techniques of analytical epidemiology.
- 15. USES OF DESCRIPTIVE EPIDEMIOLOGY 1. Useful in providing data with regard to the types of disease problems and their magnitude in community. (mortality and morbidity rates and ratios) 2. Provides information on the etiology of the disease and helps in formulating an etiological hypothesis. 3. Provides background data required for the planning, organizing, and evaluating preventive and curative services. 4. Leads the path for further research with regard to a particular disease problem