1. Introduction to General Epidemiology (2) By: Dr. Khalid El Tohami

2. Objectives At the end of the session the student should be able to:  Enumerate epidemiological methods  To understand the steps in each one

3. Epidemiological Methods  The primary concern of the epidemiologist is to study occurrence of disease in people.  Carefully designed research strategies must be done to explore disease aetiology.

4. Study designs Non intervention stud. (Observational) Descriptive stud.Case stud.SurveysAnalytical stud. Ecological (correlational) Cross-sectional (Prevalence) Case con. Stud. (case-reference) Cohort stud. (Follow-up) Intervention stud. (Experimental) Randomized control Trials (Clinical trials) Non-randomized trials (Quasi-experimental study)

5. Observational Studies  It allows nature to take its own course.  We measure but not intervene.

6. DESCRIPTIVE STUDY DESIGNS  Uses: Describes magnitude of the disease load in terms of morbidity and mortality rates. Provides clues to disease etiology (formulation of etiological hypothesis). Provides data for planning, organizing and evaluating health services. Contribute to research by describing variation in disease occurrence by time, place and person.

7. a/ Case studies

8. Case studies  A case study describes in depth the characteristics of one or limited number of cases in its natural environment

9. Case studies  A case may be a patient, a health centre, a village etc…  Can provide useful insight into the problem e.g. a new disease  Common in clinical medicine, social sciences, management and administration etc..

10. Case studies  Advantage:  It permits a holistic approach to the problem under investigation  Disadvantage:  Not representative

11. b/ SURVEYS

12. SURVEYS Use :  To collect information on demographic characteristics. Age, sex, education etc…  To study characteristics on health related variables. E.g. incidence rate, etc….  To study attitudes, opinions and beliefs

13. SURVEYS Surveys answer the following questions: WHEN IS THE DISEASE OCCURRING? (TIME DISTRIBUTION) WHERE IS THE DISEASE OCCURRING? (PLACE DISTRIBUTION) WHO IS AFFECTED? (PERSON DISTRIBUTION)

14. PROCEDURE 1.Define the problem under study. 2.Define the population under the study. 3.Describe the disease by TIME, PERSON and PLACE. 4.Measurement of the disease. 5. Comparing with known indices. 6.Formulation of an etiological hypothesis.

15. Analytical Studies  Analysis of the relationship between health status and other variables.  It is to test hypothesis.  Interested in individual and inference is to population.

16. A ) Ecological Studies  They look for associations between the occurrence of disease and exposure to known or suspected causes.  The unit of observation is the population or community.  Often the information about disease and exposure is abstracted from published statistics and therefore does not require expensive or time consuming data collection.

17. B) CROSS SECTIONAL STUDY  Prevalence rate study.  The relationship between the disease & other variables of interest as they exist at one particular point of time.

18. C) Case Control Study  Observations are taken from the same population over a prolonged period of time. (longitudinal)  It is a comparison between one group among which a problem present, with another group (control) where the problem is absent

19.  It determines:  whether or not a statistical association exists between a disease and a suspected factor.  The strength of the association if it exists.

20. Common Features  Both exposure and outcome have occurred before the start of the study.  Study proceeds back from effect to cause (retrospective).  Presence of a control group

21. Basic Steps  Selection of cases  Selection of controls  Matching  Obtaining data on exposure  Analysis and interpretation of results

22. D) Cohort Study A longitudinal a study in which a group of individuals are followed up for some time. A cohort is a group of persons who share common characteristics or experience within a defined time.

23. It determines: whether or not a statistical association exists between a disease and a suspected factor. The strength of the association if it exists.

24. Common Features The cohort is identified before the appearance of the investigated disease The study groups are observed over a period of time (prospective). The study proceeds from cause to effect Note: The incidence rate can be measured

25. Indications of Cohort Study 1. When there is strong suspicion of association between exposure and disease 2. When exposure is rare but the incidence is high among the exposed 3. When the attrition of study population can be minimized

26. Elements of a Cohort Study  Selection of study subjects.  Obtaining data on exposure.  Selection of comparison groups.  Follow up.  Analysis.

27. Experimental Study Designs In experimental studies the researcher manipulates a situation and measures its effect after that Type: 1- Randomized control trials 2- Non-randomized trials

28. 1) RANDOMIZED CONTROLLED TRIALS Those trials are used for assessment of methods of treatment and prevention. They include: - intervention - control groups and - randomization

29. steps 1. Drawing a protocol. 2. Selecting comparison & experimental groups 3. Randomization. 4. Manipulation (intervention). 5. Follow up. 6. Assessment of the outcome.

30. 2- Non-randomized trials

31. a. QUASI-EXPERIMENTAL STUDY DESIGNS  At least one of the characteristics of the true experiment is missing (RANDOMIZATION OR CONTROL GROUP)  Example: effect of health education of the level of participation of village population in an immunization campaign.

32. Blinding. Blinding is carried in three ways: 1.Single blind trial 2.Double blind trial 3.Triple-blind trial This is the ideal but double-blinding is the most commonly used.

33. DISADVANTAGES OF EXPERIMENTAL STUDIES  They are costly.  Ethical problems.  Feasibility is difficult.

34. Thanks