Basic measurement in epidemiology
Incidence & Prevalence
Tools of measurement in epidemiology
Epidemiological methods
Descriptive epidemiology.
Distribution of disease in term of Time, Place and Person
2. Measurement of
âȘ Mortality
âȘ Morbidity
âȘ Disability
âȘ Presence or absence or distribution of characteristic or
attributes of disease
âȘ Health care or health utilization
âȘ Demographic variables
4/25/2020Epidemiology - Dr. Animesh Gupta 2
3. 4/25/2020Epidemiology - Dr. Animesh Gupta 3
âȘ Incidence â the no. of NEW cases
occurring in a defined population
during a specified period of time".
âȘ Prevalence â all current cases (old
and new) existing at a given point in
time, or over a period of time in a
given population.
âȘ Prevalence = Incidence * Duration of
illness
5. âȘRate
âȘ It measures the occurrence of particular event in a population
during given time period.
âȘ A rate comprises the following elements - numerator, denominator,
time specification and multiplier.
âȘ Example:
Death rate = No. of death in a year/ Mid year population * 1000
4/25/2020Epidemiology - Dr. Animesh Gupta 5
6. âȘRatio
âȘ It expresses a relation in size between two random quantities.
âȘ The numerator is not a component of the denominator.
âȘProportion
âȘ It is a ratio which indicates the relation in magnitude of a part of the
whole.
âȘ The numerator is always included in the denominator.
âȘ It is usually expressed as a percentage.
4/25/2020Epidemiology - Dr. Animesh Gupta 6
7. âȘDescriptive
âȘAnalytic
âȘExperimental
âȘStudy of the occurrence and
distribution of disease
âȘFurther studies to determine the
validity of a hypothesis concerning
the occurrence of disease.
âȘDeliberate manipulation of the cause
is predictably followed by an
alteration in the effect not due to
chance
74/25/2020Epidemiology - Dr. Animesh Gupta
8. OBSERVATIONAL STUDIES
DESCRIPTIVE STUDY ANALYTICAL STUDIES
â TIME
â PLACE
â PERSON
âą ECOLOGICAL STUDY
âą CROSS SECTIONAL STUDY
âą CASE-CONTROL STUDY
âą COHORT STUDY
EXPEREMENTAL STUDIES
âą RANDOMIZED CONTROLLED TRIAL (RCT)
âąFIELD TRIAL
âąCOMMUNITY TRIAL 4/25/2020 8Epidemiology - Dr. Animesh Gupta
9. âȘ1st phase of an epidemiological investigation
âȘDescriptive analysis is limited to a description of the
occurrence of a disease in a population & identifying the
characteristics associated with it
âȘRelatively inexpensive and less time-consuming than
analytic studies.
4/25/2020Epidemiology - Dr. Animesh Gupta 9
10. âȘPatterns of disease occurrence, in terms of,
âȘWhen is the disease occurring â time distribution
âȘWhere is it occurring â place distribution
âȘWho is getting a disease â person distribution
4/25/2020Epidemiology - Dr. Animesh Gupta 10
11. âȘ Defining the population to be studied
âȘ Defining the disease under study
âȘ Describing the disease by
â Time
â Place
â Person
âȘ Measurement of disease
âȘ Comparing with known indices
âȘ Formulation of etiological hypothesis
4/25/2020Epidemiology - Dr. Animesh Gupta 11
12. âȘDefine the population in
relation to:
1. Number
2. Age
3. Gender
4. Occupation
5. Cultural and other
characteristics
âȘThe defined population
can be:
1. Whole population
2. Sample
3. Specially selected
groups
4/25/2020Epidemiology - Dr. Animesh Gupta 12
13. âȘLarge enough
âȘStable (no migration)
âȘClear on who belongs to the population
âȘCommunity participation
4/25/2020Epidemiology - Dr. Animesh Gupta 13
14. âȘThe epidemiologist defines the disease which can be
measured and identified in the defined population with a
degree of accuracy (operational definition).
âȘThis is different from the clinicianâs definition of a disease.
âȘExample - tonsillitis might be defined clinically as an
inflammation of the tonsils caused by infection, usually with
streptococcus pyogenes.
âȘOD - presence of enlarged, red tonsils with white exudate,
which on throat swab culture grow predominantly S.
pyogenes.
4/25/2020Epidemiology - Dr. Animesh Gupta 14
15. TIME PLACE PERSON
Climatic zones Age Birth order
Year, season
Month, week
Country,
region
Gender
Marital state
Family size
Height, weight
Day, hour
Duration
Urban/rural
Towns, cities,
institutions
Occupation
Social status
Education
BP.
Cholesterol,
habits
Objective of descriptive epidemiology?
This involves systemic collection and analysis of data.
4/25/2020Epidemiology - Dr. Animesh Gupta 15
17. âȘAn epidemic is the best known short term fluctuation.
âȘIt is defined as â The occurrence in a community or region
of cases of an illness or other health related events clearly
in excess of normal expectancyâ
4/25/2020Epidemiology - Dr. Animesh Gupta 17
18. âȘ A graph of time distribution ofepidemic cases is called epidemic curve.
4/25/2020Epidemiology - Dr. Animesh Gupta
19. 13
âȘ Common source epidemics-
a) Single/Point exposure
b)Continuous/Multiple exposure
âȘ Propagated epidemics
a) person to person
b)arthropod vector
c) animal reservoir
âȘ Slow(modern) epidemics
4/25/2020Epidemiology - Dr. Animesh Gupta 19
20. âȘ Single exposure
ïą It can occur due to an infectious agent or as a result of
contamination of the environment and develops within one
incubation period. Eg: Bhopal gas tragedy, Minamata
disease
ïą The epidemic curve rises and falls rapidly, usually has one
peak
ïą It tends to be explosive (i.e. clustering of cases within a short
time) 14
4/25/2020Epidemiology - Dr. Animesh Gupta 20
22. âȘ Continuous exposure
ïą It is when the exposure from the same source is prolonged
and the epidemic continues over more than one incubation
period.
ïą The epidemic reaches a sharp peak, but tails off gradually
over a longer period of time.
ïą Eg: A well of contaminated water or nationally distributed
vaccine(polio vaccine) or food; water borne cholera.
4/25/2020Epidemiology - Dr. Animesh Gupta
24. âȘThe epidemic shows gradual rise and tails off over a much
longer period of time
âȘIt is more likely to occur where there is
âȘlarge number of susceptible are aggregated
âȘregular supply of new susceptible individuals (Births,
Immigrants)
18
4/25/2020Epidemiology - Dr. Animesh Gupta 24
26. COURSE OF A TYPICAL PROPAGATED EPIDEMIC
4/25/2020Epidemiology - Dr. Animesh Gupta
27. âȘSeasonal trend-
âȘSeasonal variation is characteristic of many
communicable diseases.
âȘEg: Measles, upper respiratory tract infections(seasonal
rise during winter), Malaria, etc.
âȘNon-infectious diseases and conditions may sometimes
exhibit seasonal variation.
âȘExample - Sunstroke, hay fever
21
4/25/2020Epidemiology - Dr. Animesh Gupta 27
29. âȘSome diseases occur in cycles spread over short periods
of time (days, weeks, months or years) .
âȘEg: Influenza pandemics are known to occur at intervals
of 7-10yrs due to antigenic variations.
âȘNon-infectious conditions may also occur in this trend.
âȘEg: Automobile accidents are more frequent on
weekends.
294/25/2020Epidemiology - Dr. Animesh Gupta
30. âȘIt refers to changes in the occurrence of disease over a
long period of time.
âȘEg: Coronary disease, diabetes showing consistent
upward trend,
âȘdecline in TB, polio in developed countries during the
past 50 yrs.
4/25/2020Epidemiology - Dr. Animesh Gupta 30
32. InternationalVariation
âȘDescriptive studies have
shown that the pattern
of a disease is not the
same everywhere
âȘEg: Cancer of the
stomach is very
common in Japan, but
unusual in the US.
NationalVariation
âȘThere are variations in
disease occurrence
within countries.
âȘExample:
âȘEndemic goitre,
âȘFluorosis
âȘMalaria
âȘNutritional deficiencies
4/25/2020Epidemiology - Dr. Animesh Gupta 32
33. âȘDue to differences in population density, levels of
sanitation, deficiencies of medical care, education and
environment factors, there exists a rural-urban variation
âȘChronic bronchitis, cardiovascular diseases, accidents are
more frequent in urban than rural areas.
âȘSkin and zoonotic diseases and soil transmitted helminths
may be more frequent in rural than urban areas
4/25/2020Epidemiology - Dr. Animesh Gupta 33
34. âȘThese variations can be
studied with the help of âspot
or shadedâ maps.
âȘIf the map showed clustering,
it may suggest a common
source of infection.
âȘEg: Study of Cholera epidemic
by John Snow in 1854
4/25/2020Epidemiology - Dr. Animesh Gupta 34
35. âȘWay of distinguishing genetic and environmental factors.
âȘStudy of genetically similar groups but living under
different environmental conditions.
âȘ Eg: Twins
âȘStudy of genetically different groups living in a
similar environment.
âȘ Eg: Men of Japanese origin living in USA have higher rate of
coronary heart disease than the Japanese in Japan
4/25/2020Epidemiology - Dr. Animesh Gupta 35
37. âȘCross sectional study â Prevalence
âȘIt is based on a single examination of a cross section of
population at one point in time.
âȘMore useful for chronic diseases
âȘLongitudinal Study â Incidence
âȘThe observations are repeated in the same population
over a prolonged period of time by means of follow up
examination.
âȘLongitudinal is more useful, but it is time consuming.
âȘMortality, Morbidity & Disability
4/25/2020Epidemiology - Dr. Animesh Gupta 37
38. âȘMaking comparison
âȘAsking question
âȘIt helps to
âȘArrive at clues to the diseaseâs etiology
âȘIdentify groups at increased risk
4/25/2020Epidemiology - Dr. Animesh Gupta 38
39. âȘIt is a supposition, arrived at from observation or
reflection
âȘIt should specify following:
âȘ Population
âȘ Specific cause being considered
âȘ Expected outcome â the disease
âȘ Dose-response relationship
âȘ Time-response relationship
4/25/2020Epidemiology - Dr. Animesh Gupta 39
40. âȘContributes to research by describing variations in
disease occurrence by time, place and person
âȘClues to disease epidemiology â aetiological
hypothesis
âȘData regarding magnitude of disease load and types of
disease problems in community in terms of morbidity
and mortality
âȘBackground data for planning, organizing and
evaluating preventive and curative services
4/25/2020Epidemiology - Dr. Animesh Gupta 40
41. âȘEpidemiological methods (Classification)
âȘDescriptive epidemiology
âȘDefining the population
âȘDefining the disease under study
âȘDescribing the disease
âȘMeasurement of disease
âȘComparing with known indices
âȘFormulation of etiological hypothesis
âȘUses
4/25/2020Epidemiology - Dr. Animesh Gupta 41
Steps