DESCRIPTIVE STUDIES

1. DESCRIPTIVE STUDIES Dr. A.K.AVASARALA MBBS, M.D. PROFESSOR & HEAD DEPT OF COMMUNITY MEDICINE & EPIDEMIOLOGY PRATHIMA INSTITUTE OF MEDICAL SCIENCES, KARIMNAGAR, A.P. INDIA : +91505417 avasarala@yahoo.com

2. LEARNING OBJECTIVES LEARNER SHOULD BE ABLE TO KNOW AT THE END OF THIS LECTURE 1. WHAT IS MEANT BY DESCRIPTIVE STUDIES? 2. WHAT TYPES OF DESCRIPTIVE STUDIES ARE AVAILABLE? 3. WHAT COMPONENTS OF THE DISEASE AND POPULATIONS ARE TO BE DESCRIBED?

3. PERFORMANCE OBJECTIVES STUDENT SHOULD BE ABLE TO 1. CHOOSE THE SUITABLE DESCRIPTIVE STUDY FOR THE DISEASE AND POPULATION 2. Describe any health problem in terms of time, place and person 3. Interpret his findings to formulate a worthy hypothesis

4. DESCRIPTIVE STUDIES THEY ARE SO CALLED BECAUSE THEY DESCRIBE ALL ASPECTS OF 1) THE DISEASE AND 2) THE POPULATION AFFECTED

5. PURPOSE • TO FORMULATE WORTHY HYPOTHESES ULTIMATELY FOR TAKING HEALTH ACTION

6. UNIT OF THE STUDY THESE DESCRIPTIVE STUDIES ARE MAINLY CARRIED OUT IN POPULATIONS OR ITS SUB GROUPS, NOT ON INDIVIDUALS

7. NATURE OF THE STUDY • OBSERVATIONAL IN NATURE • IN DESCRIPTIVE METHOD, WE JUST OBSERVE THE EVENTS OCCURRING AND WE DO NOT INTERVENE, HENCE ALSO CALLED OBSERVATIONAL STUDIES

8. TYPES • ECOLOGICAL OR CORRELATIONAL STUDIES • CROSS-SECTIONAL OR PREVALENCE STUDIES • LONGITUDINAL OR INCIDENCE STUDIES

9. ECOLOGICAL STUDIES-1 • STUDIES CONDUCTED IN SPECIFIC POPULATION GROUPS (E.G. MUSLIMS, CATHOLICS, JEWS ETC) HAVING SPECIFIC CHARACTERISTICS IN A SPECIFIED GEOGRAPHICAL AREA

10. ECOLOGICAL STUDY METHOD • CAUSES OR RISK FACTORS ARE STUDIED WITH REGARD TO THE DISEASES AND DEATHS OCCURRED IN A PARTICULAR POPULATION. • BOTH ARE LINKED TOGETHER AND THEIR CO-OCCURRENCE (CORRELATION) IS ESTABLISHED IN THESE STUDIES FOR HYPOTHESIS FORMATION.

11. ECOLOGICAL CORRELATION FREQUENCY AND TRENDS OF THE SUSPECTED CAUSES/ RISK FACTORS PREVALENCE OR INCIDENCE OF THE DISEASE OCCURING IN A PARTICULAR AREA CORRELATED WITH

12. NON- SENSE CORRELATION THIS STUDY OF CO-OCCURRENCE DOES NOT SPEAK OF THE CAUSAL ASSOCIATION ALWAYS ONE MUST BEWARE OF NON- SENSE CORRELATION

13. ADVANTAGES AND DISADVANTAGES ADVANTAGES: • CONDUCTED AT GROUP LEVEL, NOT AT INDIVIDUAL LEVEL, HENCE RELATIVELY EASY TO DO AND QUICK • USE EXISTING DATA • GENERATE AND SUPPORT NEW HYPOTHESES • ECOLOGICAL STUDIES CONDUCTED OVER TIME ON A SPECIFIC GEOGRAPHICAL AREA ARE MORE CONVENIENT TO PERFORM AND FORM HYPOTHESES RATHER THAN STUDYING WHOLE POPULATIONS OR ITS SAMPLES AS DONE IN DESCRIPTIVE STUDIES.

14. ECOLOGICAL FALLACY • ECOLOGICAL FALLACY IS AN ERROR IN INFERENCE THAT OCCURS WHEN ASSOCIATION OBSERVED BETWEEN VARIABLES OF A GROUP LEVEL, IS ASSUMED TO EXIST AT AN INDIVIDUAL LEVEL.

15. EXAMPLES OF ECOLOGICAL STUDIES • CANCER CERVIX IS RARE IN JEWISH WOMEN DUE TO MALE CIRCUMCISION • SICKLE CELL DISEASE IS MORE SEEN IN INDIAN TRIBES

16. CROSS-SECTIONAL STUDIES (PREVALENCE STUDIES) THESE ARE SO CALLED BECAUSE A CROSS SECTION OF A COMMUNITY (FREQUENTLY TOTAL POPULATION SAMPLES) IS STUDIED AT A PARTICULAR POINT OR PERIOD OF TIME.

17. NATURE OF THE STUDY • THEY CAN BE OF DESCRIPTIVE NATURE WHEN ONE VARIABLE OR EACH VARIABLE IN A GROUP OR POPULATION IS STUDIED OR • OF ANALYTICAL TYPE AS THEY ARE SOUGHT TO PROVIDE INFORMATION ABOUT THE PRESENCE AND STRENGTH OF ASSOCIATION

18. WHEN TO CONDUCT PREVALENCE STUDIES? • THEY ARE CONDUCTED FOR CHRONIC DISEASES HAVING HIGH PREVALENCE WITH VERY LOW INCIDENCE.

19. PREVALENCE STUDY METHODOLOGY-1 IT CAN BE DONE AT A SINGLE POINT OF CALENDAR TIME (POINT PREVALENCE) WHEN THE MEASUREMENT OF CAUSAL RELATIONSHIP RELATE TO THE SAME POINT IN STUDY MEMBERS’ LIVES OR CAN BE COMPLETED IN FEW MONTHS OR YEARS (PERIOD PREVALENCE).

20. PREVALENCE STUDY METHODOLOGY-2 • THE DESCRIPTIVE INFORMATION IS OBTAINED BY MEANS OF DOOR TO DOOR SURVEY. • THOUGH THEY ARE USUALLY CARRIED OUT ON POPULATIONS OR SAMPLES OF POPULATION, THEY ARE INDIVIDUAL BASED i.e. THEY SEEK THE INFORMATION OF ABOUT THE INDIVIDUALS IN A GROUP OR POPULATION.

21. RAPID METHODS OF PREVALENCE STUDIES • CLUSTER SURVEYS • COMPUTER SIMULATION • RANDOM DIGIT DIALING FOR SAMPLING • COMPUTER BASED INTERVIEWS & USE OF SPREADSHEET

22. PUBLIC HEALTH USES • WHEN THE CROSS-SECTIONAL STUDIES ARE REPEATEDLY DONE, THEY WILL SERVE THE PURPOSE OF HEALTH AND DISEASE SURVEILLANCE OF THE POPULATION.

23. DISADVANTAGES • TIME CONSUMING AND EXPENSIVE • SUBJECTED TO RECALL BIAS AND CONFOUNDING BIAS • OTHER COMMON BIASES ENCOUNTERED IN THESE STUDIES ARE OF BERKESONIAN, INFORMATION AND INVESTIGATOR TYPES • UNDER- REPRESENT PEOPLE WITH A SHORT-COURSE OF DISEASE • LIMITED TO STUDIES OF CAUSES THAT ARE OF LONG STANDING NATURE

24. LONGITUDINAL STUDIES IN A LONGITUDINAL STUDY DESIGN, THE STUDY IS CONDUCTED AT TWO OR DIFFERENT POINTS OF TIME IN THE LIFE TIME OF INDIVIDUALS UNDER STUDY IN CONTRAST TO THE ONE TIME STUDY OF CROSS-SECTIONAL DESIGN.

25. METHODOLOGY DEFINING AND DESCRIBING THE POPULATION AFFECTED (REFERENCE POPULATION AND STUDY POPULATIONS) DEFINING AND DESCRIBING THE DISEASE OPERATIONAL CASE DEFINITIONS TIME, PLACE AND PERSON TRENDS) FORMULATION OF HYPOTHESIS

26. POPULATION AT RISK

27. REFERENCE POPULATIONS THE POPULATION WHICH IS AT RISK AND THE HEALTH ACTION HAS TO BE INITIATED AFTER THE STUDY IS OVER IS THE REFERENCE POPULATION OR THE POPULATION IN WHICH A PARTICULAR DISEASE OR EXPOSURE HAS OCCURRED AND IS TO BE INVESTIGATED REFERENCE POPULATION IS THE ONE, WHICH HAS TO BE GET BENEFITED AFTER OUR DESCRIPTIVE STUDY.

28. STUDY POPULATION THIS IS THE POPULATION ON WHICH THE HYPOTHESIS IS ACTUALLY STUDIED AND TESTED. • IT MAY BE THE ENTIRE REFERENCE POPULATION ITSELF (IF IT IS SMALL AND FEASIBLE FORSTUDY) OR • A REPRESENTATIVE PORTION OF IT(SAMPLE).

29. DESCRIBING THE STUDY POPULATION • AGE COMPOSITION, • SEX COMPOSITION, • OCCUPATIONS, • SOCIOECONOMIC STATUS, • LITERACY PROFILE • SOCIAL CUSTOMS, HABITS • SPECIFIC LIFESTYLES • KNOWLEDGE OF HEALTH FACILITIES AVAILABLE AND THEIR UTILIZATION

30. VITAL REQUIREMENTS OF STUDY POPULATION 1. ITS REPRESENTATIVENESS TO THE PARENT REFERENCE POPULATION 2. ITS OPTIMUM SIZE THEN ONLY THE RESULTS OF HYPOTHESIS TESTED ON ANY STUDY POPULATION CAN BE GENERALIZED TO THE REFERENCE POPULATION.

31. DEFINING AND DESCRIBING THE DISEASE • DEFINING THE DISEASE (CASE DEFINITION) AN OPERATIONAL WORKING DEFINITION TO MAKE UNIFORM AND UNBIASED COUNTING IN POPULATIONS

32. TIME DISTRIBUTION • EPIDEMIC • ENDEMIC • SPORADIC • CYCLICAL TRENDS • SEASONAL TRENDS • SECULAR TRENDS

33. PLACE DISRIBUTION • INTERNATIONAL VARIATIONS • NATIONAL VARIATIONS • URBAN-RURAL COMPARISONS • CLUSTERING OF DISEASE • DISEASE MAPPING

34. PERSON DISTRIBUTION • AGE INFLUENCE • RACE, RELIGION & ETHNICITY • MARITAL STATUS • SOCIOECONOMIC STATUS (SES) • MIGRATION • PERSONAL HABITS • LIFESTYLES

35. APPLICATIONS • TO FORMULATE CAUSAL HYPOTHESIS. • INDICATE THE DISEASE LOAD AND FREQUENCY ALTERATIONS AND THEREBY HELP TO MAKE FUTURE PROJECTIONS. • DIAGNOSING AND TELLING THE PROGNOSIS.

36. JURISDICTION • THE DIVIDING LINE BETWEEN THE DESCRIPTIVE AND ANALYTICAL STUDIES IS NOT VERY SHARP

37. ECOLOGICAL AND INDIVIDUAL LEVELS OR CONTEXTS • THE HYPOTHESIS TO BE STUDIED WILL BE MORE MEANINGFUL WHEN IT IS APPLICABLE AT BOTH ECOLOGICAL AND INDIVIDUAL LEVELS OR CONTEXTS AND ALSO EXPLAINS THE ECOLOGICAL (GROUP)TO INDIVIDUAL CORRELATION.

38. FORMULATION OF HYPOTHESIS SOURCES TO FORM HYPOTHESIS? 1) DESCRIPTIVE STUDIES 2) ECOLOGICAL STUDIES ON SPECIFIC GROUPS 3) KEEN OBSERVATION OF THE DATA/INFORMATION AVAILABLE 4) INDUCTIVE REASONING (MILL’S CANNONS) 5) DEDUCTIVE REASONING

39. DATA AND HYPOTHESIS • KEEN OBSERVATION OF ANY DATA, COLLECTED FOR SPECIFIC PURPOSE, ANY PURPOSE OR WITHOUT PURPOSE CAN ALSO YIELD INFORMATION FOR HYPOTHESES FORMING.

40. SUMMARY Descriptive epidemiology is hence rightly called the hypothesis forming stage of epidemiological sequence as descriptive epidemiology is very useful in providing immense information regarding the various variables like time, place, person, clustering, etc to form the hypothesis.