2. How these inferences are
arrived
Normal pulse rate 60-90/minute
Measles & chicken pox mostly occurs during
spring
Cancer of stomach more common in Japanese
Lung cancer is common among smokers
Paracetomol is 90% effective in headache
Metronidazole is effective against Amoebiasis
3. Epidemiology
What is epidemiology ?
We study health and disease
1. By observing individuals
2. By laboratory of experimental animals
3. By measuring the distribution of health
problem in population
Third one is epidemiology – putting people into
groups
4. John snow- epidemic of
cholera
Located the home of each person of cholera
in London 1854
Found out association between source of
water supply and cholera
Cholera – spread by contaminated water
before discovery of the organism of cholera
6. British Doctors Study
By Doll & Hill
The relationship between cigarette smoking
& lung cancer in 1950 a follow up study on
British doctors
7. Epidemiology
Epidemiology derived from Greek word
Epi-- on or upon
demos-- people
logos-- the study
The study upon the people or population
8. Definition
The study of the distribution and
determinants of health related states or
events in specified population, and the
application of this study to control of health
problems
Disease frequency
Disease distribution
Disease determinants
9. Disease frequency
Epidemiology is concerned with the frequency and
pattern of health events in a population
Measurements of frequency of disease, disability or
death in the form of rates and ratios
Rates are essential for the comparison of frequency
in different population
Comparison may yield important clue for the
etiology or formulation of etiological hypothesis
10. Distribution of disease
Time characteristics include annual occurrence,
seasonal occurrence and daily or even hourly
occurrence during an epidemic
Place characteristics include geographic variation,
urban- rural differences.
Personal characteristics include age, sex, race,
marital status, socioeconomic status, Behaviour and
environmental exposure
This aspect of study is called as descriptive study
11. Descriptive epidemiology provides what,
when, and where of health related events
What is the event or disease?
What is the magnitude?
When did it happen?
Where did it happen?
Who are affected?
The important out come distribution study is
formulation of etiological hypothesis
12. Determinants of disease
Test the etiological hypothesis and identify the
underlying causes or risk factors of disease
This aspect of epidemiology is Analytical
epidemiology
Which provides why and how of such events by
comparing groups with different rates of disease
occurrence.
By searching the differences in the characteristics
between the diseased and healthy
13. Making comparison
The basic approach in epidemiology is to
make comparison and draw conclusion
By comparison we try to find out curial
differences in the host and environmental
factors between those affected and not
affected
Basic tools of measurement are necessary
for the comparison –rates, ratio and
proportion
14. Rate
There were 500 deaths from motor vehicle
accident in city A
In epidemiology compare the rates of
accident in city a with city B
Rate – elements denominator, numerator,
time specification and multiplier.
Crude rates
Specific rates
Standardized rates
15. Ratio
Another measure of disease frequency
Shows the relation in size between two
quantities
The numerator not a component of the
denominator
Sex ratio, doctor population ratio, child
woman ratio etc.
16. Proportion
Shows the relation in magnitude of the part of
the whole
The numerator is always included in the
denominator
Proportional mortality rate
17. Measurements of mortality
Mortality data provides the starting point for
many epidemiological studies.
Mortality data is relatively easy to collect and
reasonably accurate
The basis of mortality data is the death
certificate
18. International death certificate
For national and international comparison a
standardized system of recording and
classification death
Part I – deals with immediate
cause( pneumonia) and underlying cause of
death( strangulated hernia)
Part II – deals with associated disease that
contributed to the death( diabetes)
19. Limitation of mortality data
Incomplete reporting of death
Lack of accuracy
Lack of uniformity
Choosing a single cause of death
Changing coding system
Diseases with low fatality
20. Uses mortality data
Can explain the trends and differences in
overall mortality
Help in prioritization for health action
Allocation of scares resource
For assessment and monitoring of public
health programmes
Gives important clue for epidemiological
research
21. Commonly used mortality
rates and ratio
Crude death rate – simplest measure, lack
comparability
Specific death rate – age, disease, income, religion
etc.
Case fatality- killing power of disease for acute and
not chronic
Proportional mortality rate –cause, age etc. can be
used when population data are not available
Survival rate- usually for five years
Standardized rates – direct and indirect
22. Measurements of morbidity
Any departure, subjective or objective, from
a state of physiological well-being
Sickness, illness, disability
Measured by
1. Persons who are ill
2. Illness frequency( spells of illness)
3. The duration
23. Incidence rate
The number of NEW cases occurring in a
defined population during a specific period of
time.
Incidence
Number of new cases of specific
Disease during a given time period
Population at risk during that period
X 1000
24. Uses of incidence rate
Taking action to control disease
Research into the etiology or causation
Research into the pathogenesis
Studying distribution of disease
Test the efficacy of preventive and
therapeutic measures
Used for formulating and testing the
hypothesis
25. Special incidence rates
Attack rate
Used only when the population is exposed to
risk for a limited period of time such as during
an epidemic
Usually expressed as a percentage
26. Secondary attack rate
The number of exposed person developing
the disease within the range of the incubation
period following exposure to primary case
SAR
Number of exposed person developing the disease
within the range of the incubation period
Total number of exposed/ susceptible contacts
X100
27. Secondary Attack Rate
Limited to application in infectious diseases
In disease where there are numerous sub-
clinical cases
Useful to determine the disease of unknown
etiology is communicable or not
Useful in evaluating the effectiveness of
control measures – immunization
28. Prevalence
All current cases ( old or new) existing at a
given point of time or over a period of time in
a given population
Point prevalence
Period prevalence
29. Start of illness
Duration of illness
Incidence - case 3,4,5 & 8
Jan 1 Dec 31
Case 1
Case 2
Case 3
Case 4
Case 5
Case 6
Case 7
Case 8
Point prevalence Jan 1- 1, 2 & 7
Point prevalence Dec 31- 1,3,5 & 8 Period prevalence Jan-Dec- 1,2,3,4,5,7,&8
Number of cases Jan- Dec
30. Relationship between prevalence &
incidence
• Depends upon two factors, incidence &
duration
P = I X D
Prevalence = incidence X mean duration
Longer the duration of the disease the greater the prevalence
A decrease in incidence & duration will decrease prevalence
31. • For chronic diseases (TB)- high
prevalence rate relative to incidence
• For acute diseases ( food poisoning,
diarrhoea)- prevalence is relatively low
compared to incidence
• For acute disease- no prevalence ( No of
episodes)
• Treatment decreasing the duration will
decrease the prevalence
• Treatment preventing death but no
recovery will increase the prevalence
32. Uses of prevalence
• To estimate the magnitude of
health/disease problems in a community
• Identify potential high risk population
• Useful for administrative & planning
purpose ( No of hospital beds, man power
need, rehabilitation facilities)
33. Aims of epidemiology
To describe the distribution and magnitude of
health and disease problem in human
population
To identify etiological factors in the
pathogenesis of disease
To provide data essential to the planning,
implementation and evaluation of services for
the prevention, control and treatment of
disease and setting up priorities
34. Epidemiology and Clinical
medicine
Epidemiology Clinical medicine
Population at risk Case or cases
Both sick and healthy Only sick
Relevant data by studying group or
population
History taking Sign and
symptoms Lab investigation
Patient comes to the doctor Investigator goes to the
community
A knowledge of prevalence, etiology and prognosis derived from
epidemiological research is important to the clinician for the
diagnosis and management of individual patient