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Chapter-02 Epidemiological Studies

BOOK TITLE: Epidemiology: Principles and Practice

Author
1. Bhattacharya Susmita
ISBN
9788184489248
DOI
10.5005/jp/books/11177_2
Edition
1/e
Publishing Year
2010
Pages
45
Author Affiliations
1. Rajarshi Chhatrapati Shahu Maharaj Government Medical College, Kolhapur, Maharashtra India, Rajarshi Chhatrapati Shahu Maharaj Government Medical College, Kolhapur, Maharashtra, India, All India Institute of Medical Sciences, Rishikesh, Uttarakhand, India
Chapter keywords

Abstract

Epidemiology is study of distribution and determinants of disease and health related states. Answer to six questions is searched in epidemiological studies. Questions are-who, how many, when, where and how are they affected; and what can be done to prevent and control events at present and in future. Epidemiological studies are of two types: 1. observational and 2. experimental. Observational studies are—descriptive studies and analytical studies. In descriptive epidemiology disease or health related events are studied in relation to time, place and person. They are studies done on community; not on individuals. Descriptive data on person includes -age, gender, ethnicity, occupation, etc. Disease is described in relation to geographical area; it can be presented as spot map. Time pattern tells about changes in prevalence and seasonality. Co- relational studies, case series and cross sectional surveys are types of descriptive studies. Descriptive studies are useful for formulating hypothesis; it is first step in any epidemiological study. Analytical epidemiology is used to test the hypothesis. It is observational and is of two types—case control studies and cohort studies. In case control study enquiry is from effect to cause; essentially retrospective. Cases are persons with disease and controls are without disease. Risk is estimated by odds ratio. Cohort studies test the hypothesis. Enquiry is from cause to effect. Types of cohort studies are—prospective cohort study, retrospective cohort study, prospective and retrospective cohort study, nested cohort study. Bias can occur in both case control and cohort study; it leads to misclassification and results become invalid. Cohort study measures incidence, Relative risk and Attributable risk. Clinical trials are experimental epidemiological studies. They can randomize or non-randomize. Randomized trials are of three types—therapeutic, intervention and preventive trial. Ethical considerations are very important issues in clinical trials. Bias can be minimized by using blinding techniques. Community trials are similar to clinical trials. In these intervention is given to one community and control community does not receive it. These are useful for planning interventions of health programs.

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