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THE STUDY DESIGNS
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THE STUDY DESIGNS

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  1. THE STUDY DESIGNS A STUDY DESIGN IS A SPECIFIC PLAN OR PROTOCOL FOR CONDUCTING THE STUDY, WHICH ALLOWS THE INVESTIGATOR TO TRANSLATE THE CONCEPTUAL HYPOTHESIS INTO AN OPERATIONAL ONE.

  2. CRITERIA FOR SELECTION OF THE RIGHT DESIGN • RELEVANT :DESIGN ALLOWS YOU TO ANSWER YOUR RESEARCH QUESTION • NOVEL :DESIGN ALLOWS MEANINGFUL CONTRIBUTION TO EXISTING KNOWLEDGE ~ NEW INSIGHTS

  3. FEASIBLE DESIGN ALLOWS STUDY TO BE DONE WITHIN AVAILABLE TIME AND FUNDS SIMPLE ALWAYS AVOID ALLUNNECESSARY COMPLEXITIES

  4. THE BASIS OF A GOOD RESEARCH IS AN APPROPRIATE STUDY DESIGN MANY CLASSIFICATIONS FOR THE RESEARCH DESIGNS RESULTING IN CONFUSION AND DILEMA

  5. THE STUDY DESIGNS ARE CLASSIFIED INTO: DESCRIPTIVE STUDY DESIGNS: AIM TO SEARCH FOR FACTS. ANALYTICAL STUDY DESIGNS: AIM TO SEARCH FOR CAUSES. EXPERIMENTAL STUDY DESIGNS: AIM TO PUT SOLUTION INTO ACTIONS.

  6. MAIN TYPES OF EPIDEMIOLOGIC STUDIES

  7. EPIDEMIOLOGIC STUDY DESIGNS

  8. Hierarchy of Epidemiologic Study Design

  9. STUDY DESIGNS THE DESCRIPTIVE STUDY DESIGNS: THESE STUDIES ARE CONCERNED WITH OBSERVING THE DISEASE DISTRIBUTION OR HEALTH RELATED EVENTS AND EVENTS SEEM TO BE ASSOCIATED WITH THE DISEASE.

  10. WHEN IS THE DISEASE OCCURRING? (TIME DISTRIBUTION) WHERE IS THE DISEASE OCCURRING? (PLACE DISTRIBUTION) WHO IS AFFECTED? (PERSON DISTRIBUTION)

  11. THE PROCEDURES IN THE DESCRIPTIVE STUDIES DEFINE THE DISEASE UNDER THE STUDY. DEFINE THE POPULATION UNDER THE STUDY. DESCRIBE THE DISEASE BY TIME, PERSON AND PLACE. MEASUREMENT OF THE DISEASE. COMPARING WITH KNOWN INDICES. FORMULATION OF AETIOLOGICAL HYPOTHESIS.

  12. SURVEY A SURVEY IS A SIMPLE DECRIPTIVE DESIGN AND USUALLY DEFINED AS COLLECTION OF DATA FROM ALL INDIVIDUALS OR A SAMPLE OF INDIVIDUALS CHOSEN TO BE REPRESENTATIVE OF THE POPULATION FROM WHICH THEY ARE DRAWN.

  13. CROSS SECTIONAL STUDY PREVALENCE RATE STUDY, DISEASE FREQUENCY STUDY. THE RELATIONSHIP BETWEEN THE DISEASE & OTHER VARIABLES OF INTEREST AS THEY EXIST AT ONE PARTICULAR POINT OF TIME

  14. ). ).

  15. CROSS-SECTIONAL STUDIES DETERMINE THE PRESENCE (PREVALENCE) OF BOTH EXPOSURE AND DISEASE IN THE SUBJECTS AND DO NOT DETERMINE THE DEVELOPMENT OF DISEASE OR RISK OF DISEASE (INCIDENCE).

  16. MOREOVER, SINCE BOTH EXPOSURE AND DISEASE ARE DETERMINED IN AN INDIVIDUAL AT THE SAME POINT IN TIME, IT IS NOT POSSIBLE TO ESTABLISH THE TEMPORAL RELATION BETWEEN EXPOSURE AND DISEASE—

  17. THAT IS, THAT THE EXPOSURE PRECEDED THE DISEASE, WHICH WOULD BE NECESSARY FOR DRAWING ANY CAUSAL INFERENCE.

  18. THUS, A RESEARCHER MAY USE A CROSS-SECTIONAL STUDY TO DETERMINE THE RELATIONSHIP BETWEEN A PERSONAL CHARACTERISTIC THAT DOES NOT CHANGE OVER TIME, SUCH AS BLOOD GROUPING, AND EXISTENCE OF A DISEASE, .

  19. SUCH AS APLASTIC ANEMIA, BY EXAMINING INDIVIDUALS AND DETERMINING THEIR BLOOD TYPES AND WHETHER THEY SUFFER FROM APLASTIC ANEMIA

  20. DESIGN OF A CROSS-SECTIONAL STUDY DEFINED POPULATION GATHERDATA ON EXPOSURE& DISEASE NOT EXPOSED DO NOT HAVE DISEASE EXPOSED DO NOT HAVE DISEASE NOT EXPOSED HAVE DISEASE EXPOSED; HAVE DISEASE

  21. INTERPRETATION NO DISEASE DISEASE DISEASE NO DISEASE EXPOSED b b a EXPOSED a d NOT EXPOSED d NOT EXPOSED c THE FINDINGS CAN BE VIEWED IN 2X2 TABLE AS FOLLOWS: c

  22. CROSS SECTIONAL STUDY OF ELEVATED BLOOD PRESSURE MEASURE THE B.P. AMONG THE STUDY POPULATION: PREVALENCE OF HYPERTENSION. COLLECT DATA ON AGE, SEX, SOCIAL CLASS AND OCCUPATION. DETERMINE HOW PREVALENCE OF HYPERTENSION IS RELATED TO THESE VARIABLES

  23. BENEFITS OF CROSS-SECTIONAL STUDY:: FEASIBILITY: THEY ARE EASY TO CARRY OUT THE ASSOCIATED COST IS LOW. THEY MAY BE CARRIED OUT IN A RELATIVELY SHORT TIME,

  24. 4. PREVALENCE CAN BE CALCULATED: IT IS OFTEN THE MOST RELEVANT MEASURE FOR BURDEN OF DISEASE, INFORMING HEALTH CARE STRATEGIES.

  25. 5. THE MEASURE OF ASSOCIATION IS READILY AVAILABLE, FROM WHICH ONE CAN CALCULATE THE ODDS RATIO FOR THE PREVALENT DISEASE.

  26. LONGITUDINAL STUDY DESIGNS OBSERVATIONS ARE REPEATED IN THE SAME POPULATION OVER A PROLONGED PERIOD OF TIME BY MEANS OF FOLLOW UP EXAMINATIONS. THESE ARE USEFUL: STUDY THE NATURAL HISTORY OF THE DISEASE. IDENTIFY THE RISK FACTORS. DETERMINE THE INCIDENCE RATE.

  27. STUDY THE EFFECTS OF NEW INTERVENTIONS OR TRENDS OF BEHAVIOUR

  28. CASE STUDY A FORM OF SINGLE STUDY RESEARCH. UNDERTAKEN ON AN INDIVIDUAL CASE WHICH IS TYPICAL FOR THE TARGETED CASES I.E. A CASE OF CONGENITAL ANAMOLY. HISTORY OF EXPOSURE CAN BE TRACED.

  29. FORMULATION OF HYPOYHESIS AN EPIDEMIOLOGICAL HYPOTHESIS SHOULD SPECIFY: THE POPULATION: THE CHARACTERISTICS OF PERSONS. THE SPECIFIC CAUSE. THE DISEASE. THE DOSE RESPONSE RELATIONSHIP. THE TIME RESPONSE RELATIONSHIP

  30. EXAMPLES CIGARETTE SMOKING CAUSES CA LUNG. THE SMOKING OF 30-40 CIGARETTES PER DAY CAUSES LUNG CANCER IN 10 % OF SMOKERS AFTER 20 YEARS OF EXPOSURE

  31. USES OF DESCRIPTIVE STUDIES PROVIDE DATA ABOUT DISEASE LOAD. FORMULATION OF ETIOLOGICAL HYPOTHESES. DATA FOR PLANNING, EVALUATION OF CURATIVE & PREVENTIVE SERVICES. CONTRIBUTE TO RESEARCH.

  32. ANALYTICAL STUDY DESIGNS THE SUBJECT OF INTEREST IN THE ANALYTICAL DESIGNS IS THE INDIVIDUAL RATHER THAN THE WHOLE POPULATION. THE AIM IS TO TEST ETIOLOGICAL HYPOTHESIS.

  33. TWO DISTINCT TYPES OF ANALYTICAL STUDIES: CASE-CONTROL COHORT

  34. THE CASE CONTROL STUDY

  35. OFTEN CALLED RETROSPECTIVE STUDIES. IT IS BETTER NOT TO USE THIS TERM. THE COMMON FEATURES: 1. BOTH EXPOSURE & OUTCOME HAVE OCCURRED. 2. PROCEEDS BACKWARD FROM EFFECT TO CAUSE. 3. PRESENCE OF A CONTROL GROUP.

  36. BASIC STEPS SELECTION OF THE CASES & CONTROLS. MATCHING. MEASUREMENT OF EXPOSURE TO THE VARIABLE UNDER INVESTIGATION. ANALYSIS & INTERPRETATION

  37. DESIGN OF A CASE CONTROL STUDY EXPOSED NOT EXPOSED EXPOSED NOT EXPOSED DISEASE NO DISEASE CONTROLS CASES

  38. SELECTION OF CASES &CONTROLS THIS IS THE MOST IMPORTANT STEP. IT INVOLVES TWO SPECIFICATIONS: 1. DIAGNOSTIC CRITERIA: SPECIFIC DIAGNOSTIC CRITERIA OF THE DISEASE, ITS STAGING ARE TO BE STATED CLEARLY.

  39. 2. ELIGIBILITY CRITERIA: THE REQUIREMENT THAT ONLY NEWLY DIAGNOSED CASES RATHER THAN OLD ONES

  40. THE CHRONOLOGIC ORDER OF THE EXPOSURE AND DISEASE, WHICH IS EASY TO ELUCIDATE IN COHORT STUDIES, MAY BE UNCERTAIN FROM THE RESULTS OF A CASE–CONTROL STUDY BECAUSE IT MAY NOT BE POSSIBLE TO KNOW IF THE EXPOSURE OCCURRED BEFORE THE DISEASE.

  41. .FOR EXAMPLE, IF A CASE–CONTROL STUDY OF ASTHMA IN HIGH SCHOOL STUDENTS DEMONSTRATES AN ASSOCIATION WITH CAT OWNERSHIP, IT MAY BE DIFFICULT TO KNOW WHAT HAPPENED FIRST:

  42. THE PRESENCE OF CATS OR THE FIRST ASTHMA ATTACK. ONE CAN OFTEN OVERCOME THIS PROBLEM BY INCLUDING ONLY NEWLY DIAGNOSED CASES

  43. The sources of cases: 1. Hospitals. 2. The general population The selection of controls: The controls must be similar to cases as possible except for absence of disease under investigation.

  44. THE SOURCES OF CONTROLS ARE: 1. HOSPITAL CONTROLS. 2. RELATIVES. 3. NEIGHBORHOOD CONTROLS. 4. GENERAL POPULATION.

  45. HOW MANY CONTROLS ARE NEEDED? GENERALLY ONE CONTROL IS NEEDED FOR EACH CASE. IF THE STUDY GROUP IS SMALL 2,3, OR EVEN 4 CONTROLS FOR EACH CASE IS POSSIBLE.