Descriptive epidemiology is concerned with observing the distribution of diseases in human populations. It describes patterns of disease occurrence and identifies characteristics associated with the disease. The key steps in descriptive epidemiology include: defining the population and disease, describing disease distribution by person, place and time, measuring disease occurrence, comparing to other populations, and formulating an etiological hypothesis. Cross-sectional and longitudinal studies are used to measure disease. Descriptive epidemiology provides baseline data on disease problems to inform further research and public health planning.

1. DESCRIPTIVE
EPIDEMIOLOGY
PRESENTED BY:
BUSHRA FARHAN
BDS 2010 BATCH
UNDER THE GUIDANCE OF:
DR.NEHA AGARWAL
DR.AMITABH VARSHNEY
DR. N.D.GUPTA

2. EPI DEMOS LOGOS
Upon,on,befall People,population,man the Study of
EPIDEMIOLOGY

3. WHAT IS EPIDEMIOLOGY?
THE STUDY OF THE
DISTRIBUTION DETERMINANTS
OF HEALTH RELATED STATES OR EVENTS IN
SPECIFIED POPULATIONS,& THE APPLICATION OF
THIS STUDY TO THE CONTROL OF HEALTH
PROBLEMS.
-JOHN M.LAST(1988)

4. EPIDEMIOLOGICAL
METHODS
DESCRIPTIVE
EPIDEMIOLOGY
ANALYTICAL
EPIDEMIOLOGY
EXPERIMENTAL
EPIDEMIOLOGY

5. DESCRIPTIVE
EPIDEMIOLOGY
 CONCERNED WITH OBSERVATION OF THE DISTRIBUTION
OF THE DISEASE OR ANY HEALTH RELATED EVENTS IN
HUMAN POPULATIONS & THE IDENTIFICATION OF THE
CHARACTERISTICS WITH WHICH THE DISEASE OR
CONDITION UNDER STUDY SEEMS TO BE ASSOCIATED.

6. o DESCRIBES THE PATTERN OF OCCURRENCE OF DISEASE
OR A CONDITION RELATIVE TO OTHER CHARACTERISTICS
OF THE POPULATION.
o FIRST PHASE OF ANY EPIDEMIOLOGICAL
INVESTIGATION.

7. STEPS :
DEFINING THE POPULATION TO BE STUDIED.
DEFINING THE DISEASE UNDER STUDY.
DESCRIBING THE DISEASE IN TERMS OF PERSON,PLACE & TIME.
MEASUREMENT OF THE DISEASE.
COMPARING WITH KNOWN INDICES.
FORMULATING AN ETIOLOGICAL HYPOTHESIS

8. 1.DEFINING THE POPULATION
TO BE STUDIED:
DEFINED
POPULATION

9. POPULATION TO
BE STUDIED IS
DEFINED IN
TERMS OF:
TOTAL NUMBER COMPOSITION OF
THE INDIVIDUALS

10.  THE POPULATION SELECTED FOR THE STUDY SHOULD ALWAYS REMAIN
STABLE,WITHOUT ANY MIGRATION INTO OR OUT OF THE AREA.
 PARTICIPATION OF THE PEOPLE OF THE COMMUNITY CHOSEN.
 PRESENCE OF HEALTH FACILITY IN CLOSE PROXIMITY TO THE COMMUNITY.
 IMPORTANCE: IT FORMS THE POPULATION AT RISK,WHICH PROVIDES THE
DENOMINATOR FOR CALCULATING THE RATES OF FREQUENCY AND
DISTRIBUTION OF THE DISEASE.

11. 2.DEFINING THE DISEASE UNDER STUDY
 THE DISEASE NEEDS TO BE DEFINED WITH AN
 IT CLEARLY INDICATES THE CRITERIA BY WHICH THE DISEASE CAN BE
MEASURED.
OPERATIONAL
DEFINITION
WITH WHICH THE DISEASE OR CONDITION CAN BE IDENTIFIED &
MEASURED IN THE DEFINED POPULATION WITH A DEGREE OF ACCURACY.

12. 3.DESCRIBING THE DISEASE UNDER
STUDY:
 WHO?
 WHERE?
 WHEN?
PERSON
PLACE
TIME

13.  TIME DISTRIBUTION

14.  SHORT TERM FLUCTUATIONS:
EPIDEMIC
THE OCCURENCE OF CASES OF AN ILLNESS OR OTHER HEALTH RELATED
EVENTS IN A REGION OR A COMMUNITY CLEARLY IN EXCESS OF NORMAL
EXPECTANCY.

15. TYPES OF EPIDEMICS:
1.COMMON
SOURCE
•SINGLE EXPOSURE OR POINT SOURCE
•CONTINUOUS OR MULTIPLE EXOSURE
2.PROPAGATED
•PERSON TO PERSON
•ARTHROPOD VECTOR
•ANIMAL RESERVOIR
3.SLOW OR
MODERN

16. COMMON SOURCE EPIDEMICS:
SINGLE EXPOSURE
•RESPONSE OF A GROUP OF
PEOPLE TO A SOURCE OF
INFECTION OR
CONTAMINATION TO WHICH
THEY WERE EXPOSED ALMOST
SIMULTANEOUSLY.
•CASES DEVELOP WITHIN 1
INCUBATION PERIOD.
•Eg:FOOD POISONING
CONTINUOUS EXPOSURE
•EXPOSURE FROM THE SAME
SOURCE MIGHT BE
PROLONGED.
•NEED NOT BE AT THE SAME
PLACE OR AT THE SAME TIME.
•Eg:CONTAMINATED WATER

17. PROPAGATED EPIDEMIC:
a.
PERSON TO
PERSON
b.
ARTHROPOD
VECTOR
c.
ANIMAL
RESERVOIR

18.  MOST OFTEN OF INFECTIOUS ORIGIN.
 USUALLY OCCURS IN PLACES WHERE LARGE NUMBER OF SUSCEPTIBLE
INDIVIDUALS ARE AGGREGATED OR WHERE THERE IS A REGULAR SUPPLY OF
NEW SUSCEPTIBLE PERSONS,WHICH TENDS TO LOWERTHE HERD IMMUNITY.

19. 2.PERIODIC FLUCTUATIONS
SEASONAL TRENDS CYCLIC TRENDS

20. 3.LONG TERM OR SECULAR TRENDS
o CHANGES IN DISEASE FREQUENCY THAT OCCUR GRADUALLY OVER
A LONG PERIOD OF TIME.
o ORAL CANCER HAS SHOWN AN UPWARD TREND IN PAST 50 yrs
WHILE TB,TYPHOID & POLIO HAVE SHOWN A DOWNWARD TREND.

21. PLACE DISTRIBUTIONS:
THE GEOGRAPHIC PATTERN OF DISEASE PROVIDE CLUES ABOUT THE
ETIOLOGY OF DISEASE.
INTERNATIONAL
VARIATIONS
NATIONAL
VARIATIONS
RURAL-URBAN
VARIATIONS
LOCAL
DISTRIBUTIONS

22. MIGRANT STUDIES:
 EVALUATE THE ROLE OF POSSIBLE GENETIC AND ENVIRONMENTAL
FACTORS IN THE OCCURRENCE OF DISEASE IN A POPULATION.
 USUALLY OF TWO TYPES:

23. COMPARING THE RATE OF OCCURRENCE OF DISEASE FOR MIGRANTS WITH
THOSE OF THEIR KIN WHO HAVE STAYED AT HOME.
COMPARISON OF GENETICALLY SIMILAR GROUPS LIVING
UNDER DIFFERENT ENVIRONMENTAL CONDITIONS.
IF RATE OF DISEASE OCCURRENCE IN MIGRANTS SIMILAR TO
THAT OF COUNTRYOF ADOPTION OVER A PERIOD OF TIME:
ENVIRONMENTAL FACTOR

24. COMPARING THE RATE OF OCCURRENCE OF DISEASE IN MIGRANTS WITH
THE LOCAL POPULATION OF THE HOST COUNTRY.
COMPARISON OF GENETICALLY DIFFERENT GROUPS LIVING
IN A SIMILAR ENVIRONMENT.
IF RATE OF DISEASE OCCURRENCE AMONG THE MIGRANTS
ARE SIMILAR TO THEIR COUNTRY OF ORIGIN:
GENETIC FACTORS

25. PERSON DISTRIBUTION:
 AGE
 BIMODALITY
 GENDER
 ETHNIC GROUP
 OCCUPATION
 SOCIOECONOMIC STATUS
 MARITAL STATUS
 BEHAVIOUR

26. •AGE:
IT MAY ASSIST IN UNDERSTANDING THE
FACTORS RESPONSIBLE FOR THE
DEVELOPMENT OF DISEASE.
AGE MAY PRODUCE INDIRECT EFFECT
THAT MUST BE TAKEN ACCOUNT OF.
ALSO USEFUL FOR ADMINISTRATIVE
PURPOSES.

27. •BIMODALITY:
 OCCURRENCE OF TWO SEPARATE PEAKS IN THE AGE INCIDENCE OF
A DISEASE.
 INDICATES THAT MATERIAL IS NOT HOMOGENOUS,THAT ENTITY
UNDER EXAMINATION MAY BE DIVIDED INTO TWO.

28. GENDER:VARIATION IN DISEASE FREQUENCY IN MALES & FEMALES.
SOCIOECONOMIC STATUS:UPPER SOCIAL CLASS
INDIVIDUAL EXHIBIT BETTER HEALTH STATE.
MARITAL STATUS:HELPS IN INVESTIGATING POSSIBLE
INFLUENCE OF A COMMON ENVIRONMENT ON THE HEALTH OF
MARITAL PARTNERS.

29. • OCCUPATION:
 AS A MEASURE OF SOCIOECONOMIC STATUS.
 FOR IDENTIFICATION OF RISKS ASSOCIATED WITH EXPOSURE TO AGENTS
PECULIAR TO CERTAIN OCCUPATIONS.
 TO IDENTIFY GROUPS WHOSE GENERAL PATTERNS OF LIFE VARY BECAUSE
OF DIFFERENT DEMANDS MADE BY THEIR OCCUPATION.

30. • BEHAVIOUR:
 HABITS LIKE SMOKING,ALCOHOLISM,DRUG ABUSE,SEDENTARY LIFESTYLE OR
OVEREATING CAN LEAD TO
 CERTAIN INFECTIOUS DISEASES LIKE TYPHOID,CHOLERA SPREAD THROUGH
MOVEMENT OF PEOPLE IN MASSES SUCH AS IN PILGRIMAGE.
CORONARY ARTERY DISEASE,
HYPERTENSION,CANCERS,OBESITY ETC

31. 4.MEASUREMENT OF DISEASE:
DONE IN TWO TERMS:
MORBIDITY
MORTALITY
INCIDENCE PREVALENCE
EXPRESSED IN TERMS OF
LONGITUDINAL
STUDY
CROSS SECTIONAL
STUDY

33. CROSS SECTIONAL STUDIES
 A SET OF INDIVIDUALS ARE CHOSEN WHO MAY BE A REPRESENTATIVE SAMPLE
OF THE CHOSEN POPULATION.
 THE MEASUREMENTS OF EXPOSURE AND EFFECT ARE MADE AT THE SAME
TIME.
 THIS PROVIDES INFORMATION ON THE RELATIONSHIP BETWEEN A DISEASE
AND OTHER VARIABLES OF INTEREST.
 EASY & ECONOMICAL TO CARRY OUT.

34.  “CROSS SECTIONAL STUDIES DONE FOR LONGER DURATION BY REPEATING
PERIODICALLY.”
 SAME INDIVIDUALS ARE EXAMINED UPON REPEATED OCCASIONS & THE
CHANGES WITHIN GROUP ARE RECORDED IN TERMS OF ELAPSED TIME
BETWEEN OBSERVATIONS.
 BUT MORE TIME CONSUMING.
LONGITUDINAL STUDIES

35. USEFUL
FOR:
STUDYING THE
NATURAL HISTORY
OF THE DISEASE & ITS
OUTCOME.
IDENTIFYING THE
RISK FACTORS
ASSOCIATED
WITH THE
DISEASE.
CALCULATING
THE INCIDENCE
RATE OF THE
DISEASE.

36. 5.COMPARING WITH KNOWN INDICES
BY MAKING COMPARISON BETWEEN DIFFERENT POPULATIONS & SUBGROUPS OF
THE SAME POPULATION
POSSIBLE TO REACH A CONCLUSION WITH REGARD TO THE DISEASE
ETIOLOGY & TO IDENTIFY SUBGROUPS AT RISK.

37. 6.FORMULATION OF AN ETIOLOGICAL
HYPOTHESIS
HYPOTHESIS:
“A SUPPOSITION ARRIVED AT FROM BY OBSERVATION OR BY
REFLECTION”.

38. SPECIFICATIONS OF HYPOTHESIS:
POPULATION
THE CAUSE BEING
CONSIDERED
THE EXPECTED
EFFECT
DOSE-RESPONSE
RELATIONSHIP
TIME-RESPONSE
RELATIONSHIP

39. USES:
PROVIDES DATA WITH REGARD TO THE TYPES OF DISEASE
PROBLEMS & THEIR MAGNITUDE IN THE COMMUNITY.
PROVIDES INFORMATION ON THE ETIOLOGY OF A DISEASE & HELPS
IN THE FORMULATION OF AN ETIOLOGICAL HYPOTHESIS.
PROVIDES DATA REQUIRED FOR THE PLANNING,ORGANIZING &
EVALUATING PREVENTIVE & CURATIVE SERVICES.
LEADS THE PATH FOR FURTHER RESEARCH WITH REGARD TO A
PARTICULAR DISEASE PROBLEM.

40. THANK YOU!!