This document provides an overview of basic measurements used in epidemiology. It discusses tools like proportion, rate, and ratio. It also covers various measures of mortality like crude death rate, specific death rate, and proportional mortality rate. Measures of morbidity like incidence and prevalence are explained. The relationship between incidence and prevalence is described. Standardization techniques are introduced to make rates comparable between populations.
2. Learning objectives
• At the end of this lecture you sh be able
• List the various tools used for measurement
• List the various measures of death
• List the various measures of disease
2
4. Measurements used in epidemiology
• Measurement of mortality
• Measurement of morbidity
• Measurement of disability
• Measurement of natality
• Measurement of disease attributes
• Measurement of health care services
• Measurement of the risk factors
• Measurement of demographic variables
4
10. Proportion – ‘real’ example
• What proportion of the population is
suffering from diabetes?
10
11. Rate
Contains
• Numerator (which is part of denominator)
• Denominator
• Multiplier
• Time period
• Usually expressed per 100 / per 1000 population
• It has a time dimension, whereas a PROPORTION
does not
11
26. Specific death rate
• Cause specific
– Deaths due to cholera
• Age specific
– Infant deaths
• Sex specific
– Maternal deaths
• Time specific
– Weekly deaths
26
48. Crude rates
Madurai Population Deaths Death rate
per 1000
0-64 53,500 446 8.3
Chennai Population Deaths Death rate
per 1000
0-64 92,000 850 9.2
48
49. Age specific rates
Madurai Population Deaths Death rate
per 1000
0-24 21,500 123 5.7
25-64 32,000 323 10.0
Chennai Population Deaths Death rate
per 1000
0-24 32,000 150 4.6
25-64 60,000 700 11.6
49
51. Standardization for Madurai
Standard Population Madurai
rates
Expected
deaths
0-24 156,000 5.7 889
25-64 45,000 10.0 450
Total 201,000 1,339
Age Population Total deaths Standardized
crude rate
0-64 201,000 1,339 6.6
∂
∂ ∂ ∂
51
52. Standardization for Chennai
Standard Population Chennai
rates
Expected
deaths
0-24 156,000 4.6 718
25-64 45,000 11.6 522
Total 201,000 1,240
Age Population Total deaths Standardized
crude rate
0-64 201,000 1,240 6.1
∂
∂ ∂ ∂
52
53. Standardized rates
Madurai Population Deaths CDR per
1000
Std. DR
per 1000
0-64 53,500 446 8.3 6.6
Chennai Population Deaths CDR per
1000
Std. DR
per 1000
0-64 92,000 850 9.2 6.1
53
56. Standardized mortality ratio
Age Doctor
population
Observed
deaths
25-34 300 *
35-44 400 *
45-54 200 *
55-64 100 *
Total 1000 9.0
Crude death rate for doctors is 9.0 per 1000
56
57. Standardized mortality ratio
Age National
rate
Doctor
population
Observed
deaths
Expected
deaths
25-34 3 300 * 0.9
35-44 5 400 * 2.0
45-54 8 200 * 1.6
55-64 25 100 * 2.5
Total 1000 9.0 7.0
57
58. Standardized mortality ratio
SMR =
Observed deaths
Expected deaths
X 100
SMR = 9/7 X 100 = 129
It means doctors experience 29% more
mortality than the general population
58
59. Summary
• There are various measures of mortality
• Each one has its own purpose and
disadvantages
• Standardization is a method for making rates
comparable between regions
59
61. Measurement of morbidity
• Incidence
– Occurrence of new cases
• Prevalence
– Existence of new and old cases
• Incidence – how many people with the disease
are newly diagnosed each year (like video)
• Prevalence - how many people in a population
currently have the disease (like snapshot)
61
62. Incidence (நடக்குறது)
62
=
No. of 𝐍𝐄𝐖 cases of a disease
in a particular time period
Total population at risk during
the same time period
X 1000
68. Points to remember about incidence
• Refers only to new cases
• Not influenced by duration of disease
• Refers to a particular time period
• Denominator is people at risk
68
69. Prevalence (இருக்குறது)
=
No.of 𝐎𝐋𝐃 𝐚𝐧𝐝 𝐍𝐄𝐖 cases of a disease
in a particular time point/period
Total population at risk during
the same time period
X 1000
69
73. Prevalence increases
• Longer duration of disease
• Prolongation of life with treatment
• Increase in incidence
• Immigration of new cases
• Better reporting of cases
• Emigration of healthy people
73
74. Prevalence decreases
• Shorter duration of diseases
• Improved cure rate
• Decrease in incidence
• Emigration of new cases
• Under reporting of cases
• Immigration of healthy people
74
75. Uses of prevalence
• Magnitude of disease problems
• Identify potential high-risk populations
• Administrative and planning purposes, e.g.,
hospital beds, manpower needs, rehabilitation
facilities
75
78. Points to remember about prevalence
• Refers to new and old cases
• Influenced by duration of disease
• Refers to a particular time period
• Denominator is people at risk
78
80. Relation between incidence &
prevalence
• Prevalence = Incidence X duration
• Incidence = 10 cases/1000 population/year
• Mean duration of disease = 5 years
• Prevalence = 10 x 5 = 50 per 1000 population
80
81. Summary
• Incidence and prevalence are finer
measurements of health as compared to
death rates
• They help us to measure the effectiveness of
disease control measures
81
82. Take home messages
• Proportion, rate and ratio – basic tools
• CDR is a simple measure of death/health
• Standardization is needed for comparability
• Incidence reflects new cases only
• Prevalence reflects new and old cases
• Incidence and prevalence are related
• Mortality measures are important, morbidity
measures give a better idea of health
82
83. Review 1
• It was reported that the incidence of dengue
was increasing every year in Madurai. This
could mean all EXCEPT,
a) Control of mosquitoes has failed
b) Reporting of dengue cases has improved
c) Treatment for dengue has failed
d) Public awareness on dengue has increased
83
84. Review 2
• Prevalence of Diabetes is increasing every year in
India. This could mean all EXCEPT,
a) Incidence of DM is increasing
b) Reporting of diabetes has increased
c) Diabetic patients are surviving longer due to
better treatment
d) Public awareness on diabetes has increased
e) None of the above
84
85. Review 3
• Examples of a disease with high incidence but
low prevalence include (multiple options)
a) Acute respiratory infection
b) Acute diarrhoea
c) TB
d) Leprosy
85
86. Review 4
• Examples of a disease with low incidence but
high prevalence include (multiple options)
a) Acute respiratory infection
b) Acute diarrhoea
c) TB
d) Leprosy
86
87. Review 5
• A new diabetes control programme was
introduced in Madurai. After 1 year, the
incidence and prevalence of Diabetes
increased. This means
a) The programme did not work
b) The programme worked
c) Data not sufficient
87
88. Review 6
• Disadvantages of crude death rate include
(multiple options)
a) Simple measure
b) Influenced by the age composition
c) Not comparable between countries
d) All of the above
88
89. Review 7
• Proportional mortality is useful for all EXCEPT
a) Understanding relative importance of diseases
as a cause of death
b) Determining measures for reducing preventable
mortality
c) Indicating the risk for population from dying due
to a particular cause
d) All of the above
89
90. Review 8
• Standardized rates can be calculated for
a) Age
b) Sex
c) Race
d) Literacy rate
e) All the above
90
91. Review 9
• Standardized mortality ratio requires all
EXCEPT
a) Age specific denom. for interest pop.
b) Age specific death rates for standard pop.
c) Age specific death rates for interest pop.
d) Crude death rate in interest pop.
91
92. Review 10
• A patient with Atherosclerotic heart disease for 7
years developed Acute myocardial infarction last
week and died today as a result of myocardial
rupture. What is the immediate cause of death?
a) Acute myocardial infarction
b) Atherosclerotic heart disease
c) Cardiac arrest
d) Rupture of myocardium
92
93. Review 11
• Mid year population is not the denominator
for (multiple options)
a) Age specific death rate
b) Cause specific death rate
c) Crude death rate
d) Proportional mortality rate
e) Case fatality rate
93
94. THANK YOU
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