# measurement in epidemiology

```Disease frequency.
Disease
frequency.
Distribution.
Distribution
determinants.
Determinants.
Mortality.
 Morbidity.
 Disability.
 Presence &amp; absence or distribution of..
 Medical needs.
 Utilization of health services.
 Demographic variables.

Rate
Ratio
Proportion

Measures the occurrence of an event or
disease in a given population during a
given period (one Year).
(Birth rate, growth rate, accident rate)


Usually expressed per 100 or per1000
population.
It has a time dimension, whereas a
PROPORTION does not.
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A fraction is made up of 2 numbers.
The top number is called the
NUMERATOR
and the bottom number is called the
DENOMINATOR.
In the fraction &frac34; the 3 is the numerator
and the 4 is the denominator.

No of death in one year
Death rate= -------------------- X 1000
Total mid year population
Numerator
Denominator.
Time specification
Multiplier
(Numerator is part of denominator )
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The value obtained by dividing one
quantity by another- X/Y.
Male to female ratio.
A ratio often compares two rates,
death rates for women and men at a
given age.
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Ratio also expresses relation of size
between the two quantities.
Numerator is not part of Denominator.
Expressed as X / Y.
Doctor : Population ratio.
Male : Female ratio.
WBC : RBC ratio

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A part/share or number considered in
comparative relation to a whole.
&quot;the proportion of greenhouse gases
in the atmosphere is rising”
Usually expressed as a percentage %


This is also relation /magnitude between
two quantities, And numerator is always
part of denominator.
And expressed as percentage
-Proportion of female students .
-Proportion of anemic mothers
(60% mothers are anemic)
Incidence
Occurrence of new cases
•
Prevalence
Existence of all new &amp; old cases.
 Prevalence:-
how many people in
a population currently have the
disease (Photograph)
 Incidence:-
how many people are
diagnosed each year (Film)
Cure rate
New cases
Attack rate
Secondary
attack rate
• The rate at which acute
disease is spreading -used during epidemics
&amp; expressed in %.
• % of exposed persons
developing disease after
primary case exposure
Point
prevalence
Period
prevalence
• Prevalence at any
given point of time.
• 4% TB cases on 1st April
•Prevalence at a given
period of time.
•Period will be 1year.
Longer duration of the disease.
 Prolongation of life, with treatment.
 If incidence increases.
 Immigration of new cases.
 Better reporting of cases.
 Emigration of healthy people.

Incidence
increases.
Prolongation
of life
without
cure.
Longer
duration of
disease
20
Shorter duration of diseases.
 Improved cure rate.
 Incidence decreases.
 Emigration of new cases.
 Under reporting of cases.
 Immigration of healthy people.

Improved cure rate.
Short duration of
disease.
Incidence decreases
Crude Death Rate.
 Specific death rate.
 Case fatality rate.
 Proportional mortality rate.
 Survival rate.
 Standardized death rate.


Number of deaths from all causes, per
1000 estimated mid year population in
one year in a given place.
No deaths during one year
CDR = _________________________ X 1000
Mid year population
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Cause Specific death rate like

Age specific-IMR, Child Mortality rate
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Sex specific death rate – MMR/female
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Period specific death rate–Death in May

Percentage of particular cases dying
during particular disease epidemic.
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Killing power of disease particularly
acute diseases
No of deaths due to cholera

CFR= ----------------------- X 100
Total No of cholera cases
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Proportion or % of deaths due to
particular cause out of total deaths.
It measures the disease burden.
Under 5,
No of deaths below 5 years
proportional = -------------------- X 100
mortality rate
Total No all of deaths
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Percentage of the treated patients remaining
alive at the end of 5 years treatment.
Yard stick for assessing the standard of
therapy in cancer.
Survival
pts alive at the end of 5 yrs
Rate
= ---------------------- X 100
Total No of pts treated
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CDR can not be useful for comparison.

Death rate need to be standardized
for comparisons.

Standardization can be done by:adjusting death rate age wise,
:also can be done sex/race wise
```