The document outlines a presentation on descriptive epidemiology delivered by Dr. Narayanan Namboothiri, covering its definition, classification, steps, and uses. It references historical examples, including John Snow's cholera study in London, and discusses various types of descriptive studies and their methodologies. Key aspects include understanding disease occurrence through time, place, and person distributions to inform health promotion and disease prevention strategies.

1. DESCRIPTIVE EPIDEMIOLOGY
PRESENTER : DR. NARAYANAN NAMBOOTHIRI G.
GUIDED BY
: DR. (BRIG) HEMANT KUMAR
: DR. CHETHANA K.
: DR. SHREYASWI SATHYANATH

2. OUTLINE OF PRESENTATION
1. Brief on Epidemiology and classification
2. Descriptive epidemiology- Introduction &
Classification
3. Steps in Descriptive epidemiology with
examples
4. Uses of descriptive epidemiology
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3. Epidemiology
EPI DEMO LOGOS
Upon,on,befall People,population,man the Study of
The study of anything that happens to
people
“That which befalls man”
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4. WHAT IS EPIDEMIOLOGY?
“The study of Frequency, Distribution and
Determinants of health-related states or
events in specified populations and the
application of this study for the promotion of
health and prevention of diseases”
(John.M.Last,1988)
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5. FATHER OF EPIDEMIOLOGY
JOHN SNOW (1813-1858)
Another importance of John Snow?
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6. CHOLERA – THE ERA OF
DESCRIPTIVE EPIDEMIOLOGY
1854,September 1st week,London
600 people living within few blocks of the
BROAD STREET PUMP in London died
John Snow and William Farr appointed
Farr adhered to MIASMATIC THEORY
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7. MIASMATIC THEORY
• Disease was transmitted by miasm/cloud/bad
air that clung low on the surface of the earth
• So people who lived at lower altitudes are at
greater risk of contracting a disease
• Lower the elevation, higher the mortality
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8. TABLE FOR PROOF OF MIASMATIC THEORY BY
WILLIAM FARR
Deaths from Cholera in 10,000 Inhabitants by Elevation of Residence
above Sea Level, London, 1848–1849 by William Farr
* Table from Leon Gordis
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9. John Snow was not satisfied
In London a family obtains water by signing up with one
of the water companies
Intake of water were from a very polluted part of
THAMES RIVER
At one point of time,one of the companies,THE LAMBETH
COMPANY for technical reasons shift water intake from a
lesser polluted area of THAMES RIVER
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10. John snow identified pumps which
supplies water to each area and the company
that supply water through that pump
He went house to house,counted all the
deaths in each house,determines which
company supplies water to each house
(SHOE LEATHER EPIDEMIOLOGY..!!)
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11. Deaths were lower in people getting their water from
LAMBETH COMPANY when compared with others
In homes supplied by other companies, death rate was
315 per 10,000 houses, but in homes supplied by
lambeth company ,it was only
38 per 10,000 houses
Disease was transmitted by CONTAMINATED WATER
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12. TABLE FROM THE BOOK ‘ON THE MODE OF
COMMUNICATION OF CHOLERA’ BY JOHN SNOW
Deaths from Cholera per 10,000 Houses, by Source of Water Supply,
London, 1854
* Table from Leon Gordis
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13. DROP OF LONDON WATER...!!
* Leon Gordis
A cartoon by Punch in 1850 on drop of water in Thames
river,London published on Report of the General Board of
Health on the Epidemic Cholera of 1848 and 184910/25/2020 13

14. CLASSIFICATION
• Based on,
• 1. Frequency
• 2. Distribution DESCRIPTIVE Epidemiology
a) time
b) place
c) person
• 3. Determinants ANALYTIC Epidemiology
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15. DESCRIPTIVE EPIDEMIOLOGY
Simply, Study of the occurrence
and distribution of disease

16. INTRODUCTION
• First phase of an Epidemiological investigation
BASIC INSTINCT
• a. When is the disease occurring ?
Time distribution
• b. Where is it occurring?
Place distribution
• c. Who is getting the disease?
Person distribution
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17. TYPES OF DESCRIPTIVE STUDIES
1. CASE REPORTS/CASE SERIES
2. CROSS SECTIONAL DESCRIPTIVE STUDIES
3. LONGITUDINAL DESCRIPTIVE STUDIES
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18. 1. CASE REPORTS/CASE SERIES
• This type of study is based on reports of a
single, or else a series of cases of specific
treated or untreated condition without any
specific comparison (control) group
• Study is intended on :
1. Proportions
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19. 2. CROSS SECTIONAL DESCRIPTIVE STUDIES
• Done on a sample of the total population
• May be community based or hospital based
• Study is intended on :
1. “Prevalence” of a factor of interest
2. “Mean” of a factor of interest
3. Description of a Pattern
4. As a surrogate for longitudinal descriptive studies
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20. 3. LONGITUDINAL DESCRIPTIVE STUDIES
• A longitudinal descriptive study follows up a single
group of subjects over a defined period of time
• More scientific than Cross sectional ones but at the
same time more costly and time consuming
• Study is intended on :
1. ‘Incidence’ of a disease
2. ‘Natural history’ of a disease
3. ‘Trend’ of a disease
4. ‘Trend’ of a health - related phenomena
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21. STEPS/PROCEDURES
1. Defining the population to be studied
2. Defining the disease under study
3. Describing the disease by
• a. Time
• b. Place
• c. Person
4. Measurement of disease
5. Comparing with known indices
6. Formulation of an aetiological hypothesis
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22. DETAILS OF STEPS IN DESCRIPTIVE
EPIDEMIOLOGY

23. I. DEFINING THE POPULATION
• Descriptive studies are investigations of
populations, not individuals
• Population base must be defined not only in
terms of the total number, but also its
composition in terms of age, sex, occupation,
cultural characters and similar information
needed for the study.
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24. • The “Defined Population" can be the whole
population in a geographic area, or more often a
representative sample taken from it.
• It can also be ‘Specially selected groups’ such as
age and sex groups, occupational groups etc..
IMPORTANCE
• It provides the denominator for calculating rates
which are essential to measure the frequency of
disease and study its distribution and
determinants
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25. CONDITIONS TO DEFINE A POPULATION
1. Large enough so that age, sex and other specific
rates are meaningful.
2. The community chosen should be stable,
without migration into or out of the area. Eg:
visitors and guests.
3. Community participation.
4. Population should not be overtly different from
other communities in the region
5. A health facility should be close enough to
provide relatively easy access for patients
requiring medical services
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26. STEPS/PROCEDURES
1. Defining the population to be studied
2. Defining the disease under study
3. Describing the disease by
• a. Time
• b. Place
• c. Person
4. Measurement of disease
5. Comparing with known indices
6. Formulation of an aetiological hypothesis
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27. II. DEFINING THE DISEASE
• Main concern of an Epidemiologist is to obtain an
accurate estimate of disease in a population
• Needs a definition that is both precise and valid
to enable him to identify those who have the
disease from those who do not
• OPERATIONAL DEFINITION : A definition by
which the disease or condition can be identified
and measured in the defined population with a
degree of accuracy (criteria by which disease is
measured will be included)
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28. EXAMPLE-DEFINING TONSILITIS
CLINICIAN
• Inflammation of the tonsils caused by
infection, usually with streptococcus pyogenes
EPIDEMIOLOGIST
• Inflammation of tonsils which shows the
presence of enlarged, red tonsils with white
exudate, which on throat swab culture grow
predominantly S. pyogenes
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29. STEPS/PROCEDURES
1. Defining the population to be studied
2. Defining the disease under study
3. Describing the disease by
• a. Time
• b. Place
• c. Person
4. Measurement of disease
5. Comparing with known indices
6. Formulation of an aetiological hypothesis
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30. III. DESCRIBING THE DISEASE
• Describe the Occurrence and Distribution of
disease (or health-related events or
characteristics within populations) by time,
place and person
• This involves systematic collection and
analysis of data.
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31. Characteristics frequently examined
in descriptive studies
* Park,24th edition
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TIME PLACE PERSON
Year Climatic zones Age, Sex
Season Country, region Birth order , Family size
Month Urban/rural Marital state
Week Local community Height, weight
Day Towns Occupation,Blood pressure
Hour of
Onset
Cities Social status , Blood
cholesterol
Duration Institutions Education, Personal habits

32. A. TIME DISTRIBUTION
• Epidemiologists have identified three kinds of
time trends or fluctuations in disease
occurrence :
I. Short-term fluctuations
II. Periodic fluctuations, and
III. Long-term or secular trends
• Give important clues about the source or
etiology of the disease, thereby suggesting
potential preventive measures.
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33. i. Short term fluctuations
• The best known Short term fluctuation is an
Epidemic
EPIDEMIC
The occurrence of cases of an illness or other
health-related events in a community or
region clearly in excess of normal expectancy
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34. TYPES OF EPIDEMICS
A. Common - source epidemics.
(a) Single exposure or "point source" epidemics.
(b) Continuous or multiple exposure epidemics
(c) Continous or interrupted exposure
B. Propagated epidemics.
(a) Person-to-person
(b) Arthropod vector
(c) Animal reservoir
C. Slow (modern) epidemics.
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35. EPIDEMIC CURVE
• A graph of time distribution of epidemic cases
is called the Epidemic curve
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IMPORTANCE
(1) A time relationship with exposure to a
suspected source
(2) A cyclical or seasonal pattern
suggestive of a particular infection, and
common source or propagated spread of
the disease.

36. Common – source, single
exposure or point source epidemics
• Exposure to a disease agent is brief and
simultaneous.
• Cases develop within one incubation period of
the disease.
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37. Important features
Explosive (Clustering of cases within narrow interval of time)
All cases develop in one incubation period
Curve rises rapidly and falls rapidly
No secondary waves
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38. EXAMPLES
• Bhopal tragedy-India (contamination of the
environment by industrial chemicals or
pollutants),33rd Anniversary
• Minamata disease – Japan (consumption of fish
containing high concentration of methyl mercury)
• Food poisoning
• Chicken pox
• Cholera
• Measles
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39. Common – source, continous or
repeated exposure
• Exposure from the same source may be
continous, repeated or intermittent
• When an infectious agent persists in the
common vehicle for some amount of time
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40. Important features
More than one peak
Curve rises slowly, and also falls gradually
Continues beyond the range of one incubation period
There is intermittent duration of the exposure
After the source is controlled, there is decrease in disease
 Extended or irregular
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41. EXAMPLES
• Gonorrhoea outbreak – A Sex worker may be a
common source but since she will infect her
clients over a period of time there may be no
explosive rise in the number of cases
• Legionnaires disease outbreak – A respiratory
illness that resulted in an epidemic due to a
common source of Air conditioner
• Contaminated well in a village
• Nationally distributed brand foods
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42. Common – source, continous or
interrupted exposure
• There is a common source, but the source introduces the
infection into the vehicle only interruptedly
EXAMPLE
Out of the 4 nurses looking after a urological ward, 1
maybe carrier of Pseudomonas aeroginosa.
Now, as and when this particular NURSE is on duty
She would introduce the infection through the catheters
that she may be passing into the Patients
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43. Propagated Epidemics
• Most often of infectious in origin and results
from person to person transmission of an
infectious agent
(a) Person-to-person - eg: TB
(b) Arthropod vector- eg: Malaria
(c) Animal reservoir - eg: Anthrax
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44. Course of typical propagated epidemic
* Table from Park,24th edition10/25/2020 44

45. Important features
 Gradual rise and tails off over a much longer
period of time
 Transmission continues until the number of
susceptible is depleted
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EXAMPLES
1. Hepatitis A
2. TB
3. Diphtheria in school children
4. Polio
5. Malaria
6. Measles

46. ii. Periodic fluctuations
1. SEASONAL TREND
• Characteristic of many communicable
diseases.
• Related to Environmental conditions.
• Non-infectious diseases and conditions may
sometimes exhibit seasonal variation.
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47. Malaria - Average Monthly Climatology
Conditions in India
Malaria - Average Monthly Climatology Conditions in India (1970-2000)
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48. Seasonal trend of dengue/DHF in India 2005-2007
* Table from Park,24th edition
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49. EXAMPLES
• Asthma – Spring
• URTI – Winter
• GI infections – Summer
• Dengue - September
• Non infectious diseases – Sunstroke, Hay
Fever, Snake Bite
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50. 2. CYCLIC TREND
• Occur in cycle period of time
• Spread over short periods of time which may be
days, weeks, months or years.
EXAMPLES
• Influenza pandemics - at intervals of 7-10 years,
due to antigenic variations
• Rubella - every 6-9 years
• Automobile accidents in US - more frequent on
weekends, especially Saturdays
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51. Influenza virus infection –cyclic trend
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52. iii. Long term or Secular trends
• Changes in the occurrence of disease (ie, A
progressive increase or decrease) over a long
period of time, generally several years or
decades
• May have short term fluctuations imposed on
it
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53. Secular Trends of Incidence of Lung
Cancer in a developed country
* WHO_AFMC red book
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54. B. PLACE DISTRIBUTION
• All disease have a definite geographical pattern
• Environmental Factors, Genus, Socio Economic
Factors, Role of diet, Migration and other
etiological factors can be studied
• Major variations are :
1. International variations
2. National variations
3. Rural – Urban variations
4. Local variations
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55. i. International Variations
• Difference in disease pattern over different
countries
* UNAIDS,AIDSinfo 2017
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56. EXAMPLES
• Ca stomach - common in Japan
• Ca oral cavity – common in India
• Ca cervix – common in India
• Ca stomach – low in US
• Ca breast – low in Japan
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57. ii. National Variations
• Disease pattern distribution within a country
*NACO survey 2015
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58. EXAMPLES
• Endemic goitre – common in hilly areas
of North India such as JK, HP, Delhi,
Punjab, UP, Haryana (Called as GOITRE
BELT)
• HIV – More in Andhra pradesh,Tamil
nadu, Maharashtra, Karnataka, Gujarat
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59. iii. Rural – Urban Variations
• Disease pattern distribution across Rural and
Urban field areas
• Due to difference in
Population density
Social class
Deficiencies in medical care
Levels of sanitation, education
Environmental factors
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60. Rural-Urban variation of Cancer in Missouri
* The health and welfare of rural and urban cancer survivors in Missouri – Mario
schootman et al. CDC 2013
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61. EXAMPLES
Common in Urban
• C/c bronchitis
• Lung cancer
• Mental illness
• CVS diseases
• Drug dependence
Common in Rural
• Skin diseases
• Helminthic diseases
• Zoonotic diseases
• TB
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62. iv. Local variations
• Disease pattern distribution across cities,
outer city and inner-city variations
• Best studied with the aid of 'spot maps' or
'shaded maps‘
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EXAMPLES
1. Diarrhoea
2. Enteric Fever
3. Cholera

63. 10/25/2020 63

64. SPOT MAP USED BY JOHN SNOW
Spot map of Asiatic cholera in London
* Park,24th edition
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64
SPOT MAPS- These maps show at a glance areas of
high or low frequency, the boundaries and patterns
of disease distribution.

65. C. PERSON DISTRIBUTION
• By defining the persons who develop the
disease by Age, Sex, Occupation, Martial
Status, Habits, Social Class and other host
factors
• For Natural history of disease
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66. FACTORS IN PERSON DISTRIBUTION
• Age
Some diseases are more frequent in certain age
groups
Eg: Measles,chickenpox in childhood
Cancer,hypertension,diabetes in middle age
Atherosclerosis,Alzheimers in old age
BIMODALITY : Two separate peaks in disease –age
distribution
eg.- Leukemia,Hodgkins disease
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Bimodal curve for Hodgkins disease

67. • Sex
Eg: Obesity, hyperthyroidism(more In Women)
Lung Cancer, Coronary Heart Disease (More In Men)
• Ethnicity/Racial
Eg: Tuberculosis, Essential Hypertension, Coronary Heart
Disease, Cancer, And Sickle Cell Anaemia
• Marital status
Eg: Mortality Rate (Less In Married) Ca Cervix(more In
Unmarried)
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68. • Occupation
Eg : silicosis,asbestosis
• Social class
Eg : Diabetes (upper-class),
Malnutrition, TB(lower-class)
• Behaviour
Eg : Cancer, Coronary artery disease
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69. • Stress
Eg : hypertension, peptic ulcer, mental problems
• Migration
Eg : filaria, malaria
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70. STEPS/PROCEDURES
1. Defining the population to be studied
2. Defining the disease under study
3. Describing the disease by
• a. Time
• b. Place
• c. Person
4. Measurement of disease
5. Comparing with known indices
6. Formulation of an aetiological hypothesis
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71. IV. MEASUREMENT OF DISEASE
• Amount of disease load in a population
• By measurement of
1. Mortality
2. Morbidity – Incidence & Prevalence
Longitudinal studies Cross sectional studies
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72. i. Cross sectional studies (Prevalence)
• Simplest form (like a photograph)
• Single examination of a cross-section of
population at one point in time
• Results of which can be projected on the
whole population provided the sampling has
been done correctly
• More useful for chronic than short-lived
diseases
• Eg: Hypertension
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73. ii. Longitudinal studies (Incidence)
• Complex form (like a cinefilm)
• Observations are repeated in the same
population over a prolonged period of time by
means of follow-up examinations
• Uses :
To study the natural history of disease and its
future outcome
For identifying risk factors of disease
Finding out incidence
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74. RELATION B/W
PREVALANCE&INCIDENCE
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75. 10/25/2020 75

76. P = I * DP-prevelance, I-incience, D-duration
* All illustrations from Leon Gordis
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77. STEPS/PROCEDURES
1. Defining the population to be studied
2. Defining the disease under study
3. Describing the disease by
• a. Time
• b. Place
• c. Person
4. Measurement of disease
5. Comparing with known indices
6. Formulation of an aetiological hypothesis
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78. V. COMPARING WITH KNOWN
INDICES
• By making comparisons between different
populations, and subgroups of the same
population, it is possible to arrive at clues to
disease aetiology
• Eg : comparing smokers and non smokers in
the study of Lung cancer
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79. Effect of discontinuing fluoridation in Antigo, Wisconsin, November 1960.
DMF, decayed, missing, and filled teeth; FL+, during fluoridation; FL-, after
fluoridation was discontinued – *Leon Gordis
*Leon Gordis10/25/2020 79

80. STEPS/PROCEDURES
1. Defining the population to be studied
2. Defining the disease under study
3. Describing the disease by
• a. Time
• b. Place
• c. Person
4. Measurement of disease
5. Comparing with known indices
6. Formulation of an aetiological hypothesis
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81. VI. FORMULATION OF HYPOTHESIS
• A hypothesis is a supposition, arrived at from
observation or reflection
FIVE ESSENTIALS OF A HYPOTHESIS
1. The population
2. The specific cause being considered
3. The expected outcome - the disease
4. The dose-response relationship
5. The time-response relationship
(*PSE-DT )
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82. EXAMPLE OF A HYPOTHESIS
• "Cigarette smoking causes lung cancer"
(an incomplete hypothesis)
• "The smoking of 30-40 cigarettes per day
causes lung cancer in 10 per cent of smokers
after 20 years of exposure“
(a complete hypothesis)
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83. Uses of Descriptive
Epidemiology
Data regarding magnitude of the disease load
via morbidity and mortality rates
Disease aetiology
Provide background data for planning,
organizing and evaluating preventive and
curative services
contribute to research by describing variations
in disease occurrence by time, place and
person.
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84. SUMMARY
• Descriptive studies are the first steps into a
new epidemiological research (testing the
water)
• It gives answers to how many, and 3 “W”s i.e,
when,where,who
• Three important use of descriptive studies are
trend analysis, healthcare planning and
hypothesis generation
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85. TAKE HOME MESSAGE
If we consider ‘Case scenario’ as a
CINEMA, The Director will be the
Clinician, but the SCREENPLAY of the
Cinema will be written by an10/25/2020 85

86. REFERENCES
• K. Park; Park’s Textbook of Preventive and Social Medicine 24th edition 2017.
• Leon Gordis; Epidemiology, Third edition, 2004.
• http://www.epidemiology.ch/history/louis.htm
• Who AFMC book
• Brian McMahon, Epidemiology principles and methods, 1st edition 1970.
• Mario schoolman et al,The health and welfare of rural and urban cancer
survivors in Missouri – Mario schootman et al.Centre for disease control and
prevention 2013
• Kaiser family foundation based on UNAIDS,AIDS info. Accesed on November
2017
• Naco 2015 data on AIDS prevalance in India
• M.D.Gupte,Vidya Ramachandran et.al,Epidemiological profile of
India:Historical and contemporory perspectives,National institute
epidemiology,chennai
• Vivek jain text book of social and preventive medicine,8th edition
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87. THANK YOU..
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