Epidemiologists use various measurements to quantify disease occurrence in populations. Rates, ratios, and proportions are commonly used. A rate is a measure of events occurring in a population over time, comprising a numerator, denominator, time period, and multiplier. Specific rates measure events in subgroups, like infant mortality rate. A ratio expresses the relative size of two quantities. A proportion indicates the relation of a part to the whole, often expressed as a percentage. Incidence measures new disease cases over time while prevalence measures total current cases. Both help identify at-risk groups and plan health services and facilities.

1. BASIC MEASUREMENTS IN
EPIDEMIOLOGY
Lecturer:
PhD, Associate Professor Mirgul B.Yrysova.
BASIC & CLINICAL EPIDEMIOLOGY DEPARTMENT.
I.K. AKHUNBAEV KSMA.
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2. Epidemiology focuses, among other things, on
measurement of mortality and morbidity in human
populations. The scope of measurements in
epidemiology is very broad and unlimited.
Tools of measurement: The epidemiologist usually
expresses disease magnitude as a rate, ratio or
proportion.
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1. RATE:
A rate measures the occurrence of some
particular event in a population during a given
time period.
A rate comprises the following elements:
 Numerator
 Denominator
 Time specification
 Multiplier

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Total No. of events /happenings in a defined
Rate= geographical area in a defined period X K
Total No. of population exposed to those
events/happening or (risks) in same
geographical area during same period.
K = 100,1000,10 000,100 000 etc.

5. The various categories of rates are :
 Crude rates - where denominator is whole
population.
 Specific rates - where denominator is
specific segment of population.
 Morbidity rates - gives us an idea about
people who are diseased.
 Mortality rates - gives idea about people
who are dead
 Standardized rates
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Some Crude Rates
Crude
birth rate = Total No. of live births recorded at a place during a year x 1000
Total mid-year estimated population of same place during
same year
mid-year = 1st of July
1. Population at 1st Jan is less and at 31 Dec. is more
2. We have to calculate population for 365 days, so we will have 365 readings of
C.B.R (CALIFORNIA BEARING RATIO )
Crude
death rate = Total no. of deaths recorded at a place during one year x1000
total mid-year estimated population of same place
during same year

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Some Specific Rates
Infant mortality rate
Maternal mortality rate
Neo-natal mortality rate
Peri-natal mortality rate

8. 2. RATIO:
It expresses a relation in size between two random
quantities.
Ratio is the result of dividing one quantity by
another;
it is expressed in the form of: x:y or x/y
Example:
The ratio of white blood cells relative to red cells
is 1: 600 or 1/600, meaning that for each white
cell, there are 600 red cells.
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3. PROPORTION:
A proportion is a ratio which indicates the relation in
magnitude of a part of the whole.
A proportion is usually expressed as percentage.
Example:
The no. of children with scabies at certain time x 100
the total no of children in village at same time

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Measurements in Epidemiology
a) Measurement of mortality
b) Measurement of morbidity
c) Measurement of disability
d) Measurement of natality
e) Measurement of the presence, absence or distribution of the
characteristic of attributes of the disease.
f) Measurement of medical needs, health care facilities, utilization
of health services & other health related events.
g) Measurement of the presence, absence or distribution of the
environmental and other factors suspected of causing the disease.

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MORTALITY RATES AND RATIOS
1. Crude death rate
2. Specific death rate
3. Case fatality rate (not true rate)
Total no, of persons dying due
to a particular disease at a place X 1000
Case fatality rate = total no. of persons suffering from
that particular disease at same place
Case fatality rate is not a true rate because in rate you count either
whole population (e.g. C.B.R) or a segment of population (e.g.
I.M.R)
4. Proportional mortality rate
5. Survival rate
6. Adjusted or standardized rates.

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MEASUREMENT OF MORBIDITY
Three aspects of morbidity are commonly measured
by morbidity rates of ratios, namely frequency,
duration and severity.
Disease frequency is measured by incidence and
prevalence rates. The case fatality rate may be used as
an index of severity. The disability rate is used for
duration measurement.

13. INCIDENCE
DEFINITION: “The number of new cases occurring in
a defined population during a specified period of
time”.
FORMULA:
No. of new cases of specific
disease during a given time period x1000
population at risk
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14. FEATURES of INCIDENCE
It refers to only new cases
It refers during a given period.
It is in specified population.
It can also refer to new spells or episode
of disease arising in a given period of
time per 1000 population
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TYPES:
1. Attack rate
No. of new cases of a specified disease
= during a specified time interval x 100
total population at risk during same interval
2. Secondary attack rate
It is defined as the number of exposed persons developing
the disease within the range of incubation period following
exposure to a primary case.
Number of exposed persons developing
= the disease within range of incubation x 100
total no. of exposed/susceptible contacts period

16. Uses of INCIDENCE:
Incidence rate useful for controlling disease
Also used for research into aetiology and
pathogenesis, distribution of diseases, and
efficacy of preventive and therapeutic measures.
For short term planning
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17. PREVALENCE
DEFINITION:
The total number of all individuals who have an attribute or disease at
a particular time divided by the population at risk of having the
attribute or disease at this point in time or midway through the
period.
FORMULA:
total no. of individuals having an attribute or disease at a particular time x 100
population at risk of having attribute or disease at risk particular time
or midway through period
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18. TYPES:1. Point prevalence = No. of cases at time x 100
population at time
2. Period prevalence = No. of cases in an interval x 100
mid interval population
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19. USES:
1. Helps to estimate magnitude of
health/disease, problem in community
& identify high-risk populations.
2. Helpful for administrative and planning
purposes
e.g.) hospital beds, manpower facilities
etc.
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20. Thanks for attention!
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