Epidemiology DR.SOMANATH.ppt

DEPARTMENT OF PUBLIC HEALTH DENTISTRY
Dr.somanath reddy kunsi
NAVODAYA DENTAL COLLEGE

Contents
Introduction
Etymology
Definition
Components of
epidemiology
History of …
Aims & objectives of …
Uses /scope of …
Branches of …
Principles of …
Essential steps in …
Strategy of …
Who is an
epidemiologist?
Epidemiological triad
Epidemiology vs clinical
medicine
Epidemiological
approach
Tools of measurement in
epidemiology
Basic measurements in
epidemiology
Association & causation
Methods of
epidemiology

I keep six honest serving men, they taught me all I know. Their
names are –
what, when, why, how, where & who.
The power of ‘reasoning’ of humans –
The story of forbidden fruit…
“No disease is sent by evils or demons, but is the
result of natural causes”- Hippocrates
Current status
Etiology X Epidemiology
Basic science of preventive and
social medicine
Introduction
Hippocrates (460-375 B.C)

What is epidemiology ?
Etymology
Derived from Greek word Epidemic
EPI = upon/ among
DEMOS = people
LOGOS = science/ study
Definition
Study of distribution and determinants of health
related states or events in specified populations,
and the application of this study to the control of
health problems.- John M. Last (1988)

Components of epidemiology
Frequency
Basic measures – rate and ratio
Facilitates comparison
Distribution
Disease occurs in patterns
Distribution patterns by time, place & person
Determinants
To identify the underlying causes or risk factors.

History of epidemiology
Hippocrates (460-375 B.C.)
first known epidemiologist
Claudius Gallen (130- 200 A.D)
“reason alone discovers some things, experience alone
discovers some things; but to find others, requires both
reason and experience”
Thomas Syndenham (1624- 1689 A.D.)
Founder of epidemiology

John Snow (1813- 1858 A.D.)
Father of epidemiology
Investigation of Cholera
epidemic in London in
1848- 49 and 1853-54
First reported systematic epidemiologic study
…History of epidemiology

Snow’s findings
Water supply
company
Population
(1851)
No. of deaths
from cholera
Cholera death
rate per 1000
pop.
Southwark 1,67,654 844 5.0
Lambeth 19,133 18 0.9

William Budd (1811-1880)
Study on typhoid fever
Epidemiological society in London during
1850s with Earl of Shaftesbury as president
W.H. Frost (1927)
First professor of Epidemiology in U.S
R. Doll, A.B. Hill (1950, 1964)
The relationship between cigarette smoking and lung cancer
…History of epidemiology

History of Dental Epidemiology
Hippocrates
‘the third upper tooth is found to be decayed more frequently
than all the others’ Guerini (1967)
Edwin Saunders
Probably the first systematic dental epidemiological study in
Britain. Report to parliament entitled, “The teeth- a test of
age” in 1837.
John Tomes
Published a tooth mortality study in 1848
Atkinson
British journal of dental science 1863

William Fisher
Investigated public health aspects of dentistry
1885- ‘Compulsory attention to the teeth of school children’
BDA committee for study of child dental health
School dental services
The story of Mc Key and Dean
Dietary studies on humans
Vipeholm study (Gustafsson et al, 1954)
Hopewood House study (Sullivan- 1958, Harris- 1963)
Turku Sugar studies (Scheinin, Makinen et al- 1975)
…History of Dental Epidemiology

Initially limited to detection and control of
communicable diseases.
International Epidemiological Association –
Lowe and Kostrzewski (1973):
1. Describe size and distribution of disease
2. To provide data essential for planning, implementation and
evaluation of health services for prevention, control and
treatment of disease
3. Identify aetiological factors in pathogenesis of disease
Aims of Epidemiology

The ultimate aim of epidemiology is…
To eliminate or reduce the health problem
or its consequences
To promote the health and well being of
the society as a whole.

1. To collect, collate and analyze all data relating to agent,
host and environment – to describe epidemiological
situation
2. To further analyze and describe occurrence,
distribution and nature of disease- constitute social and
geographical pathology of disease
3. To probe into – in order to fill- gaps for causal factors
and its role at different stages where disease is
multifactorial
4. To help administrators to channel their policies to serve
various groups of population – to meet their needs
objectives of epidemiology

Epidemiology has evolved considerably over the
past 50 years and the major challenge now is to
explore and act upon the social determinants of
health and disease.
- (Beaglehole & Bonita, 1997).
Early studies- causes of communicable
diseases
Identification of preventive methods
Course and outcome of disease
Support to both preventive and clinical
medicine.
Determine health status of population groups
Helps health authorities to use limited resources to the best
possible effect by identifying priority health programmes
Evaluate effectiveness and efficiency of health
services
Management of MI- Lancet study
Uses / Scope of epidemiology

Achievements of epidemiology
Elimination of small pox
Methylmercury poisoning
Rheumatic fever and rheumatic heart disease
Iodine deficiency diseases
High blood pressure
Smoking, asbestos and lung cancer
HIV/AIDS
Fluoride, Dental caries & Fluorosis

Branches of epidemiology
General epidemiology
Specific epidemiology
Experimental epidemiology
Clinical epidemiology
Evaluation epidemiology
Forecasting of epidemics

Principles
1. Exact observation
2. Correct interpretation
3. Rationale explanation
4. Scientific construction

Essential steps in …
Acquire basic knowledge .. ..
Define the problem.. ..
Collect available data and formulate
hypothesis – NOT CONCLUSION
Planning answers to following questions:
Regarding collection of data –
How to analyze
How to interpret and present the report
Investigate each individual unit of the universe
of the disease – characteristics involved
Arrange for special investigations

MAC MOHAN AND PUGH:
Descriptive epidemiology
Formulation of hypothesis
Analytical epidemiology
Experimental epidemiology
Strategy of . . .

Who is an epidemiologist
Any person who researches into occurrence
of disease or disability in groups of people
is called an epidemiologist.
QUALIFICATIONS OF AN EPIDEMIOLOGIST
(SMILLIE):
Familiar with statistical techniques
Well grounded in diagnosis of disease
Thorough with H/O medicine, relating to epidemics
Good knowledge of bacteriology, immunology and
physiology
Knowledge of principles of preventive medicine

EPIDEMIOLOGICAL TRIAD
Living: bacteria, virus
Non-living:
nutrients, chemicals
MAN HIMSELF
-Age,sex
-Genetics, nutrition
-Socioeconomic status
-Living habitat, food habits
Epidemiological Triad

Sr.
no
EPIDEMIOLOGY CLINICAL
MEDICINE
1. Unit of study: defined population Individual/ case
2. Relevant data – identifies source of
infection, mode of spread, determines
future trend – control measures
Case- diagnosis-
prognosis- prescribes
treatment
3. Investigator goes into the community Patient comes to doctor
4. Conceptual – results in form of tables and
graphs
Based on biomedical
Concepts – refining
tech. of diagnosis and
treatment
Epidemiology vs. clinical medicine

Epidemiological Approach
Asking questions
Making comparisons

Asking questions
Questions answers questions
Questions related to health events
What is the event (problem)
What is the magnitude
Where did it happen
When did it happen
Who are affected
Why did it happen
Questions related to health action
What can be done
How can it be prevented in future
What are the resources required & available
What difficulties may arise & how to overcome them

Making comparisons
The epidemiologist weighs, balances and contrasts
Ensure ‘comparability’
Like can be compared with like
Methods to ensure comparability
Randomization
Matching
Standardization

Tools of measurement in …
Rate
Ratio
Proportion

It is the frequency of a disease or characteristic
/ unit size of population or group
Indicates change in some event that takes place in a
population over a period of time
Rate =
10n produces whole no.
Numerator is a part of denominator
Eg. Annual death rate
Population at risk
X 10n
No. of events in specified period
…Tools of measurement
RATE
X
Number of deaths in one year
Mid-year population
1000

RATIO
Denotes relation b/w two random quantities
Numerator is not part of denominator
Ratio is one quantity divided by the other
Ratio =
Eg:
No of children with dental caries/ children with gingivitis
Dentist – population ratio = 1 : 30,000
Male female ratio in India = 1000 : 933 (in 2001)
A
B

PROPORTION
It is a ratio, which expresses the relation in
magnitude of a part of the whole.
Numerator is part of denominator
Expressed as percentage
Eg:
EG: Among 5000 school children, 2000 had
dental caries
no. of school children with dental caries at a certain time
Total no. of children in school at same time
X 100
2000
5000
X 100 = 40 %
Proportion of carious children =

Concept of numerator and denominator
The numerator and denominator of a rate
should be similarly restricted
Numerator
Refers to number of times an event has occurred in a
population
It is a part of denominator in rate and proportion, but not in
ratio
Denominator
Numerator has little meaning, unless accompanied by
denominator
epidemiologist has to choose an appropriate denominator
while calculating a rate.
Denominator may be related to
Population
Total events taken place

Denominator related to population
Mid year population
Population estimated to be present as on the first day of July
every year.
Population at risk
Person- Time
Eg. Person- years
Person- Distance
Eg. Passenger- miles
Sub groups of the population
Eg. Age groups, sex groups, professional groups, etc.

Denominator related to events
In some cases, the denominator may be related
to the events, instead of population
Eg.
Annual rate of motor vehicle accidents in Davangere
Number of accidents in one year
Mid year population
X 1000
Number of accidents in one year
Vehicle- miles
X 1000

Basic measurements in epidemiology
Definition and criteria
Ideal requirements of definition
acceptable and applicable to use in large populations
Precise and valid
What do we measure in epidemiology?
Demographic variables
Mortality
Morbidity
Distribution of the causative or risk factors
Medical & health care needs
Availability & utilization of Medical & health care facilities

Measurement of mortality
Crude death rate
Def. The number of deaths per thousand people in a
population in a given year.
It is easy to calculate
The level of mortality is used as a public health indicator.
Number of deaths
in a year in a population
Mid- year population
X 1000

Specific death rates
a) Cause or disease specific- Eg. Tuberculosis, HIV/AIDS,
accident etc.
b) Related to specific groups- Eg. Age specific, sex specific,
profession specific etc.
Specific death rates help to identify
Etiology
Groups at risk
Specific death rate due to HIV/AIDS
Specific death rate for males
No. of deaths due to HIV/AIDS in a year
Mid- year population
X 1000
No. of deaths of males in a year
Mid- year population of males
X 1000
…Measurement of mortality

Infant mortality rate
Perinatal mortality rate
Maternal mortality ratio
No. of live- born infants who
die before age 1 in a year
No. of live births in the year
X 1000
No. of still births and deaths
within 7 days of life in a year
No. of still births + live births in the year
X 1000
No. of deaths ass. with pregnancy
or child birth in a year
No. of live births in the year
X 1000
…Specific death rates

Case fatality rate
Proportional mortality rate
Standardized rates
…Measurement of mortality
Total no. of deaths
Due to a disease
Total no. of cases of
the same disease
X 1000
No. of deaths due to
a disease in a year
Total no. of deaths
In that year
X 1000
• The overall rates adjusted for the effects of differences in population
composition, such as in age, sex etc.
• For comparison between two populations with different compositions
1. Direct standardization
2. Indirect standardization

Measurement of Morbidity
“Any departure, subjective or objective, from
a state of physiological well being”- WHO
Can be measured in terms of
frequency, duration & severity
Uses of morbidity data
Describe extent & nature of the disease and thus help in
determining priorities
Provide information, which is more useful for basic research
than that of morbidity data
A starting point for etiological studies
Useful for monitoring & evaluating disease control activities

Incidence
No. of new cases of a specific disease
occurring in a defined population during a
specified period of time
Incidence rate
Special incidence rates
Attack rate
Used when the population is exposed to risk factor for a
limited period of time
Secondary attack rate
The no. of persons exposed to the risk factor developing
the disease within the range of the incubation period
following exposure to the primary case
no. of new cases of a disease in a specified period of time
Population at risk during that period
X 10n
I =
…Measurement of Morbidity

Uses of incidence rates
Helps in taking action to control the disease
Give clues to research in to etiology and
pathogenesis of disease
Helps in the study of distribution of disease
Useful in evaluating the efficacy of preventive
and therapeutic measures

No. of cases (both old and new) in a defined
population at a specified point in time
PREVALENCE RATE (P):
Expressed as cases per 1000 or per 100 population
no. of people with disease at a specified time
no. of people in the population at risk at that time
P = X 10n
Prevalence

Types of prevalence
Point prevalence
Period prevalence
No. of all current cases of a specific disease at one point in
time in relation to a defined population
Point prevalence rate
Total no. of all current cases of a
Specific disease at a given point of time
Estimated total population at
the specific point of time
X100

Period prevalence
It is a measure that expresses total no. of cases of a disease
known to have existed at some time during a specified period
Period prevalence rate
Total no. of all current cases of a Specific
disease at a given period of time interval
Estimated total population at
the specific period of time
X100

Uses of prevalence rate
In detecting the magnitude of disease in the community
In identifying potential high risk populations
In administrative and planning purposes like, assessing
manpower needs in health services, delivery of health
services etc.
Limitations of prevalence rate
Not the ideal measure for studying etiology
Depends up on incidence and duration…

Relation b/w prevalence and incidence
Prevalence rate is dependent on both
incidence rate and disease duration.
Assuming that the population is stable, the
incidence value and the duration is
unchanging, a relationship can be established
as…
Prevalence = Incidence x Avg. duration disease.
P = I X D

Relation b/w prevalence and incidence

Association & Causation
Association need not always be causal
Three types of association
Spurious association
Indirect association
Direct (causal) association
One to one causal association
Multifactorial causation

Spurious association
In a study in UK,
Place of delivery Perinatal mortality rate
Hospital 27.8
Home 5.4
?
Home is a safer place for delivery than a hospital !!!
Finding an association when none actually existed
Selection bias

Indirect association
Yudkin & Roddy hypothesized that people who
consume a lot of sugar are more likely to have a
heart attack !!!
Bennet et al. found that…
Further experimental studies…
Confounding factors
Can be applied to reduce the disease risk
Snow’s findings…

Direct (causal) association
One-to-one causal relationship
When the factor is present, the disease is present & vice versa
Eg. Measles
Koch’s postulates that a cause must be
Necessary
Sufficient for the occurrence of the disease
Although Koch postulates are theoretically sound…
Eg. Tuberculosis
Hemolytic
Streptococci
Streptococcal tonsillitis
Scarlet fever
Erysipeals

Multi factorial causation
Non communicable, chronic diseases
…Direct (causal) association
Factor 1
Factor 2
Factor 3
Reaction at cellular level Disease
Factor 1
Factor 2
Factor 3
Reaction at cellular level Disease
+
+
Eg. Smoking, air pollution & exposure to Asbestos Lung cancer

Assessing the relationship between
a possible cause and an outcome
No
Could it be due to
Selection or
Measurement bias
Could it be due to
confounding
Could it be due to
chance
Could it be causal
Apply additional criteria
No
Probably not
Probably yes

Additional criteria for causality
Temporal association
Strength of association
Specificity of the association
Consistency of the association
Biological plausibility
Coherence of the association

Methods of epidemiology
OBSERVATIONAL EPIDEMIOLOGY
Descriptive epidemiology
Analytical epidemiology
Cross sectional
Ecological
Case- Control
Cohort
EXPERIMENTAL EPIDEMIOLOGY
Randomized control trials
Field trials
Community trials

Methods of epidemiology
Epidemiology
Observational Experimental
Descriptive Analytical RCT Field Trials
Community
Trials
Cross
sectional Ecological Case-control Cohort
WHO 1993

conclusion
Where experiment is expensive or not Possible
Statistics alone may mislead you !

References
R. Beaglehole, R. Bonita, T. Kjellstrom. Basic
Epidemiology. World Health Organization,
Geneva
K. Park. Park’s Text book of Preventive and
Social Medicine, 18th edition
Soben Peter. Essentials of Preventive and
Community Dentistry, 2nd edition

Epidemiology DR.SOMANATH.ppt

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