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.

1. Basic measurements in
epidemiology
Dr. S. A. Rizwan, M.D.,
Asst. Professor,
Department of Community Medicine,
VMCHRI, Madurai

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

3. Recap
• Define epidemiology
• Uses of epidemiology
3

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

5. TOOLS OF MEASUREMENT
5

6. Tools of measurement
• Proportion
• Rate
• Ratio
6

7. Proportion
• Usually expressed as a percentage %
– Numerator (which is part of denominator)
– Denominator
– Multiplier
– No time factor
7

8. Proportion – example
What proportion of this class are Vijay fans?
8

9. Proportion – example
What proportion of this class are Ajith fans?
9

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

12. Rate – example
12

13. Rate – example
• Death rate =
𝑁𝑜.𝑜𝑓 𝑑𝑒𝑎𝑡ℎ𝑠 𝑖𝑛 𝑜𝑛𝑒 𝑦𝑒𝑎𝑟
𝑇𝑜𝑡𝑎𝑙 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝑖𝑛 𝑡ℎ𝑎𝑡 𝑦𝑒𝑎𝑟
X 1000
13

14. Ratio
Contains
• Numerator (not part of denominator)
• Denominator
14

15. Ratio – example
15

16. Ratio – example
16

17. Ratio – example
17

18. Summary
• Epidemiology uses 3 main tools of
measurement
– Proportion
– Rate
– Ratio
18

19. MEASUREMENT OF MORTALITY
19

20. Measurement of mortality
• Crude death rate
• Specific death rate
• Proportional mortality rate
• Case fatality rate
• Survival rate
• Adjusted/standardized rates
20

21. International death certificate
21

22. Crude Death Rate
𝐶𝐷𝑅 =
𝑁𝑜.𝑜𝑓 𝑑𝑒𝑎𝑡ℎ𝑠 𝑑𝑢𝑟𝑖𝑛𝑔 𝑜𝑛𝑒 𝑦𝑒𝑎𝑟
𝑀𝑖𝑑 𝑦𝑒𝑎𝑟 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛
X 1000
22

23. Total population in Madurai in 2015
23

24. No. of deaths in Madurai in 2015
24

25. CDR in Madurai in 2015
25

26. Specific death rate
• Cause specific
– Deaths due to cholera
• Age specific
– Infant deaths
• Sex specific
– Maternal deaths
• Time specific
– Weekly deaths
26

27. Total population in Madurai in 2015
27

28. No. of deaths in Madurai in 2015
28

29. Cause of death – cholera
29

30. Cholera specific death rate in Madurai
in 2015
30

31. Proportional mortality rate
=
𝑁𝑜.𝑜𝑓 𝑑𝑒𝑎𝑡ℎ𝑠 𝑑𝑢𝑒 𝑡𝑜 𝑎 𝑝𝑎𝑟𝑡𝑖𝑐𝑢𝑙𝑎𝑟 𝑐𝑜𝑛𝑑𝑖𝑡𝑖𝑜𝑛
𝑇𝑜𝑡𝑎𝑙 𝑛𝑜.𝑜𝑓 𝑑𝑒𝑎𝑡ℎ𝑠
X 100
31

32. Total population in Madurai in 2015
32

33. No. of deaths in Madurai in 2015
33

34. Total deaths
34

35. Cause of death – cholera
35

36. Proportional mortality rate of cholera
36

37. 37
Total population (MYP)
Total deaths – all causes
Cholera deaths
CDR
Specific DR
PMR

38. Case fatality rate
CFR =
𝑁𝑜.𝑜𝑓 𝑑𝑒𝑎𝑡ℎ𝑠 𝑑𝑢𝑒 𝑡𝑜 𝑐ℎ𝑜𝑙𝑒𝑟𝑎
𝑇𝑜𝑡𝑎𝑙 𝑛𝑜.𝑜𝑓 𝑐𝑎𝑠𝑒𝑠 𝑜𝑓 𝑐ℎ𝑜𝑙𝑒𝑟𝑎
X 100
38

39. Total no. of cholera cases
39

40. No. of people died due to cholera
40

41. Total no. of cholera cases
41

42. Survival rate
• Used in research studies
• Like cancer therapy or survival
=
𝑃𝑎𝑡𝑖𝑒𝑛𝑡𝑠 𝑎𝑙𝑖𝑣𝑒 𝑎𝑡 𝑡ℎ𝑒 𝑒𝑛𝑑 𝑜𝑓 5 𝑦𝑒𝑎𝑟𝑠
𝑇𝑜𝑡𝑎𝑙 𝑛𝑜.𝑜𝑓 𝑝𝑎𝑡𝑖𝑒𝑛𝑡𝑠
X 100
42

43. What is standardization?
You: My salary has
doubled this month
Ur friend: My salary
has also doubled
43


44. What is standardization?
¥. 1 Lakh = Rs. 10 Lakh
¥. 2 Lakh = Rs. 20 Lakh
Gain = Rs. 10 Lakh
Rs. 1 Lakh
Rs. 2 Lakh
Gain = Rs. 1 Lakh
44

45. What is standardization?
Rs. 1 Lakh = $ 1,500 ¥. 1 Lakh = $ 15,000
Rs. 2 Lakh = $ 3,000 ¥. 2 Lakh = $ 30,000
Gain = $ 1,500 Gain = $ 15,000
45

46. What is standardization?
You: My salary has
doubled this month
Ur friend: My salary
has also doubled
46


47. Direct standardization
47

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

50. Standard population
Standard Population
0-24 156,000
25-64 45,000
50

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

54. Indirect standardization
54

55. Standardized mortality ratio
Age National death rate
per 1000
25-34 3
35-44 5
45-54 8
55-64 25
55

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

60. MEASUREMENT OF MORBIDITY
60

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

63. Incidence – example
JANUARY 1, 2016 DECEMBER 31, 2016
63

64. Special incidence rates
• Attack rate
• Secondary attack rate
64

65. Uses of incidence rate
• For taking action to control disease
• More suited for acute or infectious conditions
• For research
65

66. Example of use of incidence
This news article is giving only the numerators,
Without denominator, it is hard to place much importance
66

67. Example of use of incidence
67

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

70. Types of prevalence
• Point prevalence
• Period prevalence
70

71. Point prevalence – example
JANUARY 1, 2016 DECEMBER 31, 2016
71

72. Period prevalence – example
JANUARY 1, 2016 DECEMBER 31, 2016
72

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

76. Example of use of prevalence
76

77. Example of use of prevalence
77

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

79. Relation between incidence &
prevalence
79

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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