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Steps in cohort study

  1. 1. 01/09/2015COMMUNITY MEDICINE SEMINAR 1 STEPS IN COHORT STUDY
  2. 2. CONTENTS 01/09/2015COMMUNITY MEDICINE SEMINAR 2  Introduction  What is a cohort?  Elements of a cohort study  Selection of study subjects  Obtaining data on exposure  Selection of comparison groups  Follow up  Analysis  References
  3. 3. INTRODUCTION 01/09/2015COMMUNITY MEDICINE SEMINAR 3  Cohort study is a type of analytical study  Done to support or refute the existence of an association between suspected cause and disease  Prospective / longitudinal /incidence / forward looking study  CAUSE → EFFECT  Types-Prospective, Retrospective, Combination
  4. 4. 01/09/2015COMMUNITY MEDICINE SEMINAR 4
  5. 5. WHAT IS A COHORT ??? 01/09/2015COMMUNITY MEDICINE SEMINAR 5  COHORT-a group of people who share a common characteristic or experience within a defined time period.  STUDY AND CONTROL COHORTS  Both should be free of disease, equally susceptible to the disease, and both groups should be comparable to each other.
  6. 6. FRAMEWORK OF COHORT STUDY 01/09/2015COMMUNITY MEDICINE SEMINAR 6
  7. 7. ELEMENTS OF A COHORT 01/09/2015COMMUNITY MEDICINE SEMINAR 7 1.Selection of study subjects 2.Obtaining data on exposure 3.Selection of a comparison group 4.Follow up 5.Analysis
  8. 8. SELECTION OF STUDY SUBJECTS 01/09/2015COMMUNITY MEDICINE SEMINAR 8 • General population- If exposure is frequent, an appropriate sample size(exposed and unexposed) is taken from general population. • Special groups - - like selected profession, college alumini, antenatal women, etc. -exposure groups-if exposure is rare, select a cohort of persons known to have had exposure.
  9. 9. OBTAINING DATA ON EXPOSURE 01/09/2015COMMUNITY MEDICINE SEMINAR 9 To know whether they are exposed or not, and also the degree of exposure. Various methods used are:  Directly from cohort members  Review of records  Medical examination or special tests  Environmental surveys
  10. 10. SELECTION OF COMPARISON GROUPS 01/09/2015COMMUNITY MEDICINE SEMINAR 10  Internal comparisons- several sub groups based on level of exposure  External comparisons- like smokers and non smokers  Comparison with general population rates-if it is available
  11. 11. FOLLOW-UP 01/09/2015COMMUNITY MEDICINE SEMINAR 11 Regular follow up of all participants to obtain data for assessing the outcome. Few methods are-  Periodic medical examination  Review records  Routine surveillance of death records  Mailed questionnaires , telephone calls, home visits.
  12. 12. ANALYSIS 01/09/2015COMMUNITY MEDICINE SEMINAR 12  Whether any association exists between the suspected factor and the disease under study  If so, what is the strength of association COHORT DISEASE + DISEASE - TOTAL EXPOSED a b a+b NOT EXPOSED c d c+d
  13. 13. INTERPRETATION 01/09/2015COMMUNITY MEDICINE SEMINAR 13
  14. 14. REFERENCE 01/09/2015COMMUNITY MEDICINE SEMINAR 14  Park’s Textbook of PREVENTIVE AND SOCIAL MEDICINE, 23rd edition  Textbook of community medicine by AH.SURYAKANTHA, 3rd edition
  15. 15. Thank you 01/09/2015COMMUNITY MEDICINE SEMINAR 15

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