DESCRIPTIVE STUDIESDESCRIPTIVE STUDIES

Dr. A.K.AVASARALA MBBS, M.D.PROFESSOR & HEADDEPT OF COMMUNITY MEDICINE & EPIDEMIOLOGYPRATHIMA INSTITUTE OF MEDICAL SCIENCES, KARIMNAGAR, A.P.INDIA : +91505417avasarala@yahoo.com

LEARNING OBJECTIVESLEARNING OBJECTIVES

LEARNER SHOULD BE ABLE TO KNOW LEARNER SHOULD BE ABLE TO KNOW AT THE END OF THIS LECTUREAT THE END OF THIS LECTURE

1. WHAT IS MEANT BY DESCRIPTIVE 1. WHAT IS MEANT BY DESCRIPTIVE STUDIES?STUDIES?

2. WHAT TYPES OF DESCRIPTIVE STUDIES 2. WHAT TYPES OF DESCRIPTIVE STUDIES ARE AVAILABLE?ARE AVAILABLE?

3. WHAT COMPONENTS OF THE DISEASE 3. WHAT COMPONENTS OF THE DISEASE AND POPULATIONS ARE TO BE AND POPULATIONS ARE TO BE DESCRIBED?DESCRIBED?

PERFORMANCE OBJECTIVESPERFORMANCE OBJECTIVES

STUDENT SHOULD BE ABLE TOSTUDENT SHOULD BE ABLE TO

1. CHOOSE THE SUITABLE DESCRIPTIVE 1. CHOOSE THE SUITABLE DESCRIPTIVE STUDY FOR THE DISEASE AND POPULATIONSTUDY FOR THE DISEASE AND POPULATION

2. Describe any health problem in terms of time, 2. Describe any health problem in terms of time, place and personplace and person

3. Interpret his findings to formulate a worthy 3. Interpret his findings to formulate a worthy hypothesishypothesis

DESCRIPTIVE STUDIESDESCRIPTIVE STUDIES

THEY ARE SO CALLED BECAUSE THEY THEY ARE SO CALLED BECAUSE THEY DESCRIBE ALL ASPECTS OFDESCRIBE ALL ASPECTS OF

1) THE DISEASE AND 1) THE DISEASE AND

2) THE POPULATION AFFECTED2) THE POPULATION AFFECTED

PURPOSEPURPOSE

TO FORMULATE TO FORMULATE

WORTHY HYPOTHESES WORTHY HYPOTHESES ULTIMATELY FOR TAKING ULTIMATELY FOR TAKING HEALTH ACTIONHEALTH ACTION

UNIT OF THE STUDYUNIT OF THE STUDY

THESE DESCRIPTIVE STUDIES THESE DESCRIPTIVE STUDIES ARE MAINLY CARRIED OUT IN ARE MAINLY CARRIED OUT IN

POPULATIONS OR ITS SUB POPULATIONS OR ITS SUB GROUPS, NOT ON INDIVIDUALSGROUPS, NOT ON INDIVIDUALS

NATURE OF THE STUDYNATURE OF THE STUDY

OBSERVATIONAL IN NATUREOBSERVATIONAL IN NATURE IN DESCRIPTIVE METHOD, WE IN DESCRIPTIVE METHOD, WE JUST OBSERVE THE EVENTS JUST OBSERVE THE EVENTS OCCURRING AND WE DO NOT OCCURRING AND WE DO NOT INTERVENEINTERVENE, ,

HENCE ALSO CALLED HENCE ALSO CALLED OBSERVATIONAL STUDIESOBSERVATIONAL STUDIES

TYPESTYPES

ECOLOGICAL OR ECOLOGICAL OR CORRELATIONAL STUDIESCORRELATIONAL STUDIES

CROSS-SECTIONAL OR CROSS-SECTIONAL OR PREVALENCE STUDIESPREVALENCE STUDIES

LONGITUDINAL OR INCIDENCE LONGITUDINAL OR INCIDENCE STUDIESSTUDIES

ECOLOGICAL STUDIES-1ECOLOGICAL STUDIES-1

STUDIES CONDUCTED IN SPECIFIC STUDIES CONDUCTED IN SPECIFIC POPULATION GROUPS (E.G. POPULATION GROUPS (E.G. MUSLIMS, CATHOLICS, JEWS ETC) MUSLIMS, CATHOLICS, JEWS ETC) HAVING SPECIFIC CHARACTERISTICS HAVING SPECIFIC CHARACTERISTICS IN A SPECIFIED GEOGRAPHICAL IN A SPECIFIED GEOGRAPHICAL AREAAREA

ECOLOGICAL STUDY METHODECOLOGICAL STUDY METHOD

CAUSES OR RISK FACTORS ARE CAUSES OR RISK FACTORS ARE STUDIED WITH REGARD TO THE STUDIED WITH REGARD TO THE DISEASES AND DEATHS OCCURRED DISEASES AND DEATHS OCCURRED IN A PARTICULAR POPULATION. IN A PARTICULAR POPULATION.

BOTH ARE LINKED TOGETHER AND BOTH ARE LINKED TOGETHER AND THEIR CO-OCCURRENCE THEIR CO-OCCURRENCE

(CORRELATION) IS ESTABLISHED IN (CORRELATION) IS ESTABLISHED IN THESE STUDIES FOR HYPOTHESIS THESE STUDIES FOR HYPOTHESIS FORMATION. FORMATION.

ECOLOGICAL CORRELATIONECOLOGICAL CORRELATION

FREQUENCY AND TRENDS

OF THE SUSPECTED CAUSES/

RISK FACTORS

PREVALENCE OR INCIDENCE OF THE DISEASE OCCURING IN A PARTICULAR AREA

CORRELATED WITH

NON- SENSE CORRELATIONNON- SENSE CORRELATION

THIS STUDY OF CO-OCCURRENCE THIS STUDY OF CO-OCCURRENCE DOES NOT SPEAK OF THE DOES NOT SPEAK OF THE CAUSAL ASSOCIATION CAUSAL ASSOCIATION ALWAYSALWAYS

ONE MUST BEWARE OF ONE MUST BEWARE OF NON- SENSE CORRELATIONNON- SENSE CORRELATION

ADVANTAGES AND DISADVANTAGESADVANTAGES AND DISADVANTAGES

ADVANTAGES: ADVANTAGES: CONDUCTED AT GROUP LEVEL, NOT AT CONDUCTED AT GROUP LEVEL, NOT AT INDIVIDUAL LEVEL, HENCE RELATIVELY EASY TO INDIVIDUAL LEVEL, HENCE RELATIVELY EASY TO DO AND QUICKDO AND QUICKUSE EXISTING DATAUSE EXISTING DATAGENERATE AND SUPPORT NEW HYPOTHESESGENERATE AND SUPPORT NEW HYPOTHESESECOLOGICAL STUDIES CONDUCTED OVER TIME ECOLOGICAL STUDIES CONDUCTED OVER TIME ON A SPECIFIC GEOGRAPHICAL AREA ARE MORE ON A SPECIFIC GEOGRAPHICAL AREA ARE MORE CONVENIENT TO PERFORM AND FORM CONVENIENT TO PERFORM AND FORM HYPOTHESES RATHER THAN STUDYING WHOLE HYPOTHESES RATHER THAN STUDYING WHOLE POPULATIONS OR ITS SAMPLES AS DONE IN POPULATIONS OR ITS SAMPLES AS DONE IN DESCRIPTIVE STUDIES. DESCRIPTIVE STUDIES.

ECOLOGICAL FALLACYECOLOGICAL FALLACY

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

EXAMPLES OF ECOLOGICAL EXAMPLES OF ECOLOGICAL STUDIESSTUDIES

CANCER CERVIX IS RARE IN CANCER CERVIX IS RARE IN JEWISH WOMEN DUE TO MALE JEWISH WOMEN DUE TO MALE CIRCUMCISION CIRCUMCISION

SICKLE CELL DISEASE IS MORE SICKLE CELL DISEASE IS MORE SEEN IN INDIAN TRIBESSEEN IN INDIAN TRIBES

CROSS-SECTIONAL STUDIESCROSS-SECTIONAL STUDIES (PREVALENCE STUDIES (PREVALENCE STUDIES))

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

NATURE OF THE STUDYNATURE OF THE STUDY

THEY CAN BE OF DESCRIPTIVE THEY CAN BE OF DESCRIPTIVE NATURE WHEN ONE VARIABLE OR NATURE WHEN ONE VARIABLE OR EACH VARIABLE IN A GROUP OR EACH VARIABLE IN A GROUP OR POPULATION IS STUDIED POPULATION IS STUDIED

OROR OF ANALYTICAL TYPE AS THEY ARE OF ANALYTICAL TYPE AS THEY ARE SOUGHT TO PROVIDE INFORMATION SOUGHT TO PROVIDE INFORMATION ABOUT THE PRESENCE AND ABOUT THE PRESENCE AND STRENGTH OF ASSOCIATION STRENGTH OF ASSOCIATION

WHEN TO CONDUCT WHEN TO CONDUCT PREVALENCE STUDIES?PREVALENCE STUDIES?

THEY ARE CONDUCTED FOR THEY ARE CONDUCTED FOR CHRONIC DISEASES HAVING HIGH CHRONIC DISEASES HAVING HIGH PREVALENCE WITH VERY LOW PREVALENCE WITH VERY LOW INCIDENCE. INCIDENCE.

PREVALENCE STUDY PREVALENCE STUDY METHODOLOGY-1METHODOLOGY-1

IT CAN BE DONE AT A SINGLE POINT OF IT CAN BE DONE AT A SINGLE POINT OF CALENDAR TIME (POINT PREVALENCE) CALENDAR TIME (POINT PREVALENCE)

WHEN THE MEASUREMENT OF CAUSAL WHEN THE MEASUREMENT OF CAUSAL RELATIONSHIP RELATE TO THE SAME RELATIONSHIP RELATE TO THE SAME POINT IN STUDY MEMBERS’ LIVES POINT IN STUDY MEMBERS’ LIVES OR OR CAN BE COMPLETED IN FEW MONTHS CAN BE COMPLETED IN FEW MONTHS OR YEARS (PERIOD PREVALENCE).OR YEARS (PERIOD PREVALENCE).

PREVALENCE STUDY PREVALENCE STUDY METHODOLOGY-2METHODOLOGY-2

THE DESCRIPTIVE INFORMATION IS THE DESCRIPTIVE INFORMATION IS OBTAINED BY MEANS OF DOOR TO DOOR OBTAINED BY MEANS OF DOOR TO DOOR SURVEY. SURVEY.

THOUGH THEY ARE USUALLY CARRIED THOUGH THEY ARE USUALLY CARRIED OUT ON POPULATIONS OR SAMPLES OF OUT ON POPULATIONS OR SAMPLES OF POPULATION, THEY ARE INDIVIDUAL POPULATION, THEY ARE INDIVIDUAL BASED i.e. THEY SEEK THE BASED i.e. THEY SEEK THE INFORMATION OF ABOUT THE INFORMATION OF ABOUT THE INDIVIDUALS IN A GROUP OR INDIVIDUALS IN A GROUP OR POPULATION.POPULATION.

RAPID METHODS OF RAPID METHODS OF PREVALENCE STUDIESPREVALENCE STUDIES

CLUSTER SURVEYSCLUSTER SURVEYSCOMPUTER SIMULATIONCOMPUTER SIMULATIONRANDOM DIGIT DIALING FOR RANDOM DIGIT DIALING FOR SAMPLINGSAMPLINGCOMPUTER BASED INTERVIEWS COMPUTER BASED INTERVIEWS & USE OF SPREADSHEET & USE OF SPREADSHEET

PUBLIC HEALTH USESPUBLIC HEALTH USES

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

DISADVANTAGESDISADVANTAGES

1.1. TIME CONSUMING AND EXPENSIVE TIME CONSUMING AND EXPENSIVE 2.2. SUBJECTED TO RECALL BIAS AND SUBJECTED TO RECALL BIAS AND

CONFOUNDING BIASCONFOUNDING BIAS3.3. OTHER COMMON BIASES OTHER COMMON BIASES

ENCOUNTERED IN THESE STUDIES ARE ENCOUNTERED IN THESE STUDIES ARE OF BERKESONIAN, INFORMATION AND OF BERKESONIAN, INFORMATION AND INVESTIGATOR TYPES INVESTIGATOR TYPES

4.4. UNDER- REPRESENT PEOPLE WITH A UNDER- REPRESENT PEOPLE WITH A SHORT-COURSE OF DISEASESHORT-COURSE OF DISEASE

5.5. LIMITED TO STUDIES OF CAUSES THAT LIMITED TO STUDIES OF CAUSES THAT ARE OF LONG STANDING NATUREARE OF LONG STANDING NATURE

LONGITUDINAL STUDIESLONGITUDINAL STUDIES

IN A LONGITUDINAL STUDY IN A LONGITUDINAL STUDY DESIGN, DESIGN,

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

METHODOLOGYMETHODOLOGY

DEFINING AND DESCRIBING THE DEFINING AND DESCRIBING THE POPULATION AFFECTED POPULATION AFFECTED ((REFERENCE POPULATION AND STUDY REFERENCE POPULATION AND STUDY POPULATIONS)POPULATIONS)

DEFINING AND DESCRIBING THE DEFINING AND DESCRIBING THE DISEASE DISEASE

OPERATIONAL CASE DEFINITIONS OPERATIONAL CASE DEFINITIONS

TIME, PLACE AND PERSON TRENDS)TIME, PLACE AND PERSON TRENDS)

FORMULATION OF HYPOTHESISFORMULATION OF HYPOTHESIS

POPULATION AT RISKPOPULATION AT RISK

REFERENCE POPULATIONSREFERENCE POPULATIONS

THE POPULATION WHICH IS AT RISK AND THE THE POPULATION WHICH IS AT RISK AND THE HEALTH ACTION HAS TO BE INITIATED AFTER HEALTH ACTION HAS TO BE INITIATED AFTER THE STUDY IS OVER IS THE REFERENCE THE STUDY IS OVER IS THE REFERENCE POPULATION POPULATION

OR OR THE POPULATION IN WHICH A PARTICULAR THE POPULATION IN WHICH A PARTICULAR

DISEASE OR EXPOSURE HAS OCCURRED AND DISEASE OR EXPOSURE HAS OCCURRED AND IS TO BE INVESTIGATEDIS TO BE INVESTIGATED

REFERENCE POPULATION IS THE ONE, REFERENCE POPULATION IS THE ONE, WHICH HAS TO BE GET BENEFITED AFTER WHICH HAS TO BE GET BENEFITED AFTER OUR DESCRIPTIVE STUDY. OUR DESCRIPTIVE STUDY.

STUDY POPULATIONSTUDY POPULATION

THIS IS THE POPULATION ON THIS IS THE POPULATION ON WHICH THE HYPOTHESIS IS WHICH THE HYPOTHESIS IS ACTUALLY STUDIED AND TESTED.ACTUALLY STUDIED AND TESTED. IT MAY BE THE ENTIRE REFERENCE IT MAY BE THE ENTIRE REFERENCE POPULATION ITSELF (IF IT IS SMALL POPULATION ITSELF (IF IT IS SMALL AND FEASIBLE FORAND FEASIBLE FOR STUDY) STUDY)

OR OR

A REPRESENTATIVE PORTION OF A REPRESENTATIVE PORTION OF IT(SAMPLE). IT(SAMPLE).

DESCRIBING THE STUDY DESCRIBING THE STUDY POPULATIONPOPULATION

AGE COMPOSITION,AGE COMPOSITION, SEX COMPOSITION,SEX COMPOSITION, OCCUPATIONS,OCCUPATIONS, SOCIOECONOMIC STATUS,SOCIOECONOMIC STATUS, LITERACY PROFILELITERACY PROFILESOCIAL CUSTOMS, HABITSSOCIAL CUSTOMS, HABITSSPECIFIC LIFESTYLES SPECIFIC LIFESTYLES KNOWLEDGE OF HEALTH FACILITIES KNOWLEDGE OF HEALTH FACILITIES AVAILABLE AND THEIR UTILIZATIONAVAILABLE AND THEIR UTILIZATION

VITAL REQUIREMENTS OF VITAL REQUIREMENTS OF STUDY POPULATIONSTUDY POPULATION

1. ITS REPRESENTATIVENESS TO THE 1. ITS REPRESENTATIVENESS TO THE PARENT REFERENCE POPULATIONPARENT REFERENCE POPULATION

2. ITS OPTIMUM SIZE2. ITS OPTIMUM SIZE

THEN ONLY THE RESULTS OF THEN ONLY THE RESULTS OF HYPOTHESIS TESTED ON ANY STUDY HYPOTHESIS TESTED ON ANY STUDY POPULATION CAN BE GENERALIZED POPULATION CAN BE GENERALIZED TO THE REFERENCE POPULATION. TO THE REFERENCE POPULATION.

DEFINING AND DESCRIBING DEFINING AND DESCRIBING THE DISEASETHE DISEASE

DEFINING THE DISEASE DEFINING THE DISEASE (CASE DEFINITION) (CASE DEFINITION)

AN OPERATIONAL WORKING AN OPERATIONAL WORKING DEFINITION TO MAKE UNIFORM AND DEFINITION TO MAKE UNIFORM AND UNBIASED COUNTING IN UNBIASED COUNTING IN POPULATIONSPOPULATIONS

TIME DISTRIBUTIONTIME DISTRIBUTION

EPIDEMICEPIDEMIC

ENDEMICENDEMIC

SPORADICSPORADIC

CYCLICAL TRENDSCYCLICAL TRENDS

SEASONAL TRENDSSEASONAL TRENDS

SECULAR TRENDSSECULAR TRENDS

PLACE DISRIBUTIONPLACE DISRIBUTION

INTERNATIONAL VARIATIONSINTERNATIONAL VARIATIONS

NATIONAL VARIATIONSNATIONAL VARIATIONS

URBAN-RURAL COMPARISONS URBAN-RURAL COMPARISONS

CLUSTERING OF DISEASE CLUSTERING OF DISEASE

DISEASE MAPPING DISEASE MAPPING

PERSON DISTRIBUTIONPERSON DISTRIBUTION

AGE INFLUENCEAGE INFLUENCE

RACE, RELIGION & ETHNICITYRACE, RELIGION & ETHNICITY

MARITAL STATUSMARITAL STATUS

SOCIOECONOMIC STATUS (SES)SOCIOECONOMIC STATUS (SES)

MIGRATIONMIGRATION

PERSONAL HABITSPERSONAL HABITS

LIFESTYLESLIFESTYLES

APPLICATIONSAPPLICATIONS1.1. TO FORMULATE CAUSAL TO FORMULATE CAUSAL

HYPOTHESIS. HYPOTHESIS.

2.2. INDICATE THE DISEASE LOAD AND INDICATE THE DISEASE LOAD AND FREQUENCY ALTERATIONS AND FREQUENCY ALTERATIONS AND THEREBY HELP TO MAKE FUTURE THEREBY HELP TO MAKE FUTURE PROJECTIONS.PROJECTIONS.

DIAGNOSING AND TELLING THE DIAGNOSING AND TELLING THE PROGNOSIS.PROGNOSIS.

JURISDICTIONJURISDICTION

THE DIVIDING LINE BETWEEN THE THE DIVIDING LINE BETWEEN THE DESCRIPTIVE AND ANALYTICAL DESCRIPTIVE AND ANALYTICAL STUDIES IS NOT VERY SHARPSTUDIES IS NOT VERY SHARP

ECOLOGICAL AND INDIVIDUAL LEVELS OR CONTEXTS

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

FORMULATION OF HYPOTHESIS FORMULATION OF HYPOTHESIS

SOURCES TO FORM HYPOTHESIS?SOURCES TO FORM HYPOTHESIS?

1) DESCRIPTIVE STUDIES 1) DESCRIPTIVE STUDIES 2) ECOLOGICAL STUDIES ON SPECIFIC 2) ECOLOGICAL STUDIES ON SPECIFIC

GROUPSGROUPS3) KEEN OBSERVATION OF THE 3) KEEN OBSERVATION OF THE DATA/INFORMATION AVAILABLEDATA/INFORMATION AVAILABLE4) INDUCTIVE REASONING (MILL’S 4) INDUCTIVE REASONING (MILL’S

CANNONS)CANNONS) 5) DEDUCTIVE REASONING5) DEDUCTIVE REASONING

DATA AND HYPOTHESISDATA AND HYPOTHESIS

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

SUMMARYSUMMARY

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