epidemiology- prcples, methods & limits(ppt) f.pptx

Epidemiology : Principles, Methods and
Limitations
By : DR. KAYNAT BUKHARI
For feedback on this lecture please mail on –feedback@igmpi.ac.in
Centre for Health Management and Research,
IGMPI
Centre for Health Management and Research, CHMR
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Objectives
 INTRODUCTION
 HISTORY
 DEFINITION
 COMPONENTS
 AIMS
 Difference of Epidemiology & Clinical Medicine
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Cont:-
 EPIDEMIOLOGICAL APPROACH
 USES
 TOOLS
 Epidemiology Data Sources & Collection Methods
 LIMITATIONS
 TERMINOLOGIES
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What is Epidemiology???
 Epidemiology is derived from Greek word “epidemic”
 EPI – up on
 DEMOS – people
 LOGOS – study
 Epidemiology means the study of disease in human population.
 Epidemiology is the basic science of preventive and social
medicine.
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HISTORY OF EPIDEMIOLOGY
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HIPPOCRATES
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History
 Hippocrates is the first person known to have examined the relationships
between the occurrence of disease and environmental influences.
 Hippocrates believed sickness of the human body to be caused by an
imbalance of the four humors (black bile, yellow bile, blood, and
phlegm).
 The cure to the sickness was to remove or add the humor in order to
balance the body.
 He coined the terms endemic and epidemic
 Endemic - for diseases usually found in some places but not in others
 Epidemic - for diseases that are seen at some times but not others
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Definitions of Epidemiology:
 As per Perkins (1873) It is that branch of science which
treats of epidemics.
 As per Frost (1927) it is the science of mass phenomenon
of infectious disease.
 As per Greenwood (1934) The study of any disease as a
mass phenomena.
 As per McMahon (1960) The study of the distribution and
determinants of disease frequency in man.
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DEFINITION:
 “Epidemiology is the study
of the distribution
(frequency, pattern) and
determinants (causes,
risk factors) of health-
related states or events in
specified populations, and
the application of this
study to the control of
health problems”
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Epidemiology Purposes in Public Health
Practice

Components:-
 Epidemiology often more concerned with the wellbeing of
society as a whole, than with the wellbeing of individuals.
 Three components are common:-
 Study of the disease frequency (frequency of disease,
disability or death and summarizing in the form of rates
and ratios)
 Study of the distribution (pattern of disease i.e. time, place,
person)
 Study of the determinants (underlying cause or risk factors)
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Components of Epidemiology
1) Disease frequency (rate or ratio)
2) Distribution of disease (Time, place & person)
3) Determinants of disease (Cause or risk factor)
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Disease frequency
 Measurement of frequency of disease, disability or
death, and summarizing this information in the form of
rates and ratios (e.g. prevalence rate, incidence rate,
death rate, etc) thus the basic measure of disease
frequency is rates or ratio.
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DISTRIBUTION
An important function of epidemiology is to study the
distribution patterns in various subgroups of the population by
time, place, and person.
 TIME :- WHEN OCCURRED
 PLACE :- WHERE IT OCCURRED
 PERSON :- AGE, SEX, RACE, OCCUPATION
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DISTRIBUTION(Cont:)
That is, the epidemiologist examines :-
 whether there has been an increase or decrease of disease
over time span
 whether there is a higher concentration of disease in one
geographic area than others
 whether the disease occurs more often in men or in a
particular age-group, and
 whether most characteristics or behaviour of those affected
are different from those not affected.
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DETERMINANTS
Causes and other factors that influence the occurrence of disease
and other health-related events
OR
A unique feature of epidemiology is to test and identify the
underlying causes or risk factors of disease.
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Aims of Epidemiology
• According to IEA (International Epidemiological Association)
1.To describe the distribution and magnitude of health and disease
problems in human population.
2. To identify the aetiological factors and risk factors in pathogenesis of
disease.
3. To provide data essential to planning, implementation and evaluation
of services for prevention, control and treatment of diseases and setting
of priorities among the services.
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Ultimate Aim of Epidemiology
1. To eliminate or reduce the health problems of
community.
2. To promote the health and well-being of
society as a whole.
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Difference of Epidemiology & Clinical Medicine
CLINICAL MEDICINE EPIDEMIOLOGY
1.The unit of study is case or cases 1. Unit of study is the population
2. Concerned with disease in person 2. Concerned with disease pattern in
population both sick & healthy
3. Clinician gives diagnosis and treatment
& prognosis of the case.The diagnostic
techniques are refined and modified
3. Epidemiologist is interested in the
source of infection, mode of spread &
trend of disease. Evaluates the outcome of
preventive & therapeutic measure & give
clue to administrator for effective
management
4.The patient goes to the clinician. 4. Epidemiologist goes to the community.

Epidemiological Approach
The epidemiological approach to the problems of
health and disease is based on two major foundations
 Asking Questions
 Making comparisons
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Asking Questions
 Epidemiology has been defined as “a means of learning or asking
questions… and getting answers that lead to further questions.”
Related to health Events
a. What is the problem?
b. What is its Magnitude?
c. Where did it happen?
d. When did it happen?
e. Who are affected?
f. Why did it happen?
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Cont:-
 Questions Related to Health Action
a. What can be done to reduce the problem?
b. How can it be prevented?
c. What action should be taken by the community?
By the Health Services? By other sectors?
d. What resources are required?
e. How are the activities to be organized?
f. What difficulties may arise in implementation?
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Making Comparisons
The basic approach in epidemiology is to make comparisons and
draw inferences.
• Comparison between two or more groups (one group having
disease or exposed to risk factors and the other group not having
disease or not exposed to risk factors, or comparison between two
individuals).
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Uses of Epidemiology
1. In health care management
• Making Community diagnosis
• Planning and evaluation of health services.
• Developing health policies.
2. Understanding disease process
• Studying natural history of disease.
• Searching for causes and risk factors.
• Historic studies of rise & fall of disease.
• Identification of syndromes.
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Cont:-
3. Uses in public health practice
• Investigation of epidemics
• Surveillance of disease
• Making projection for future
• Formulating medical teaching curricular
4. Assisting in Clinical Practice
• Assessing effectiveness of treatment modalities
• Assessing effectiveness of preventive modalities
• Studying prognostic factor
• Studying effectiveness of diagnostic modalities
• Assisting in clinical decision making
• Indispensable for basic planning, conducting and analyzing clinical research
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Tools of Measurement
Basic tools of measurement in epidemiology are:-
 Rates
 Ratio
 Proportions
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RATE (DISEASE FREQUENCY)
 In epidemiology, a rate measures the occurrence of some particular
event(development of disease or the occurrence of death) in a
defined population during a specified period of time.
Death rate : No. of deaths in one year x1000
Mid –year population
These rates are essential for comparing disease frequency in different
populations or subgroups of the same population in relation to
suspected causal factors.
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RATIO
RATIO is the number or quantity of one item in comparision to the
other.
 Both the items are not a part of each other (numerator is not a part of
denominator).
 Broadly, ratio is the result of dividing one quantity by other.
 It is expressed in the form of-
x:y or x
y
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Cont:-
Eg 1: Ratio of WBC relative to RBC is 1:600
Eg 2: The no. of children with scabies at a certain time
The no. of children with malnutrition at a certain time
Other egs includes:
 Sex ratio
 Doctor-population ratio
 Child-women ratio etc
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PROPORTION :
A proportion is the comparison of a part to the whole.
 It is a type of ratio in which the numerator is included in
the denominator.
 A proportion is usually expressed as a percentage.
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PROPORTION :
Example :
The no. of children with scabies at a certain time x100.
The total no. of children in the village at the same time
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Data Sources and Collection Methods
 Data collection is a systematic process of gathering and
measuring information on variables of interest.
 Epidemiological data are different from experimental data, and
refer to various nonexperimental observations, including
population exposure levels and health effect values observed from
the samples.
 Accurate data collection is essential to maintaining the integrity of
research.
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Sources of epidemiological data
 Epidemiologists use primary and secondary data sources to
calculate rates and conduct studies.
 Primary data is the original data collected for a specific purpose by or for an
investigator. For example, an epidemiologist may collect primary data by
interviewing people who became ill after eating at a restaurant in order to
identify which specific foods were consumed.
 Collecting primary data is expensive and time-consuming, and it usually is
undertaken only when secondary data is not available.
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Sources of epidemiological data
Secondary data is data collected for another purpose by other
individuals or organizations. Examples of sources of secondary
data that are commonly used in epidemiological studies include :
birth and death certificates
 population census records
patient medical records
 disease registries
 insurance claim forms and billing records
public health department case reports
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Important Sources of epidemiological
information
Hospital inpatient records.
Outpatient clinic records.
Disease notifications.
Workplaces and schools.
Special surveys.
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Limitations
 Long periods of follow up needed. Attrition is a problem as long
follow up is required.
 Epidemiology depends on valid data. This can often be difficult to
obtain in emergency situations.
 Health workers in remote communities often lack the resources to
conduct adequate data collection and lack of access may also present
difficulties in communicating these data in a timely manner.
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Terminology used in Epidemiology
INFECTION:
 The entry and development or
multiplication of an
infectious agent in the body
of man or animal.
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ENDEMIC
 Constant presence of a
disease or infectious agent
within a given geographic
area or population group,
without importation from
outside throughout the
year in certain parts of
country.
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EPIDEMIC
 An epidemic is the
rapid spread of
disease to a large
number of people in
a given population
within a short
period of time. Also
known as Outbreak
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PANDEMIC
 An epidemic which
spreads from
country to country
or over the whole
world. For eg:
covid
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SPORADIC
The cases occurs
irregularly, haphazardly
from time to time and
generally infrequently.
E.g.. Polio
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ZOONOSES
Diseases or infections
which are transmitted
from non-human
(animal) to humans.
eg. Rabies, plague
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INCUBATION PERIOD
 This is the time interval
between the entry of the
disease agent into the
body and the appearance
of first sign and symptom
of the disease.
 For example, the
incubation period of
chickenpox is 14-16 days
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CARRIER
 A carrier is an individual
who carries and is capable
of passing on a genetic
mutation associated with a
disease and may or may not
display disease symptoms.
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ISOLATION
 A separation of a person
with infectious disease
from contact with other
human beings for the
period of communicability
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CONTAGIOUS
 A disease that is
transmitted through
contact. Eg. STD and
Leprosy.
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RESERVOIR
 The habitat ( place
for living) where
an infectious agent
living, grows and
multiplies
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FOMITES
 Objects or materials
which are likely to
carry infection, such
as clothes, utensils,
and furniture.
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VECTOR
 Usually an arthropod
eg. Mosquito which
transfers an infectious
agent from an infected
person to a healthy
person
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Thank You
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epidemiology- prcples, methods & limits(ppt) f.pptx

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