Download - Basic measurements in epidemiology
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
3
Recap
• Define epidemiology• Uses of epidemiology
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
5
TOOLS OF MEASUREMENT
6
Tools of measurement
• Proportion• Rate • Ratio
7
Proportion
• Usually expressed as a percentage %– Numerator (which is part of denominator)– Denominator– Multiplier– No time factor
8
Proportion – exampleWhat proportion of this class are Vijay fans?
9
Proportion – exampleWhat proportion of this class are Ajith fans?
10
Proportion – ‘real’ example
• What proportion of the population is suffering from diabetes?
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
12
Rate – example
13
Rate – example
• Death rate = X 1000
14
Ratio
Contains• Numerator (not part of denominator)• Denominator
15
Ratio – example
16
Ratio – example
17
Ratio – example
18
Summary
• Epidemiology uses 3 main tools of measurement– Proportion– Rate – Ratio
19
MEASUREMENT OF MORTALITY
20
Measurement of mortality
• Crude death rate• Specific death rate• Proportional mortality rate
• Case fatality rate
• Survival rate• Adjusted/standardized rates
21
International death certificate
22
Crude Death Rate
X 1000
23
Total population in Madurai in 2015
24
No. of deaths in Madurai in 2015
25
CDR in Madurai in 2015
26
Specific death rate
• Cause specific– Deaths due to cholera
• Age specific– Infant deaths
• Sex specific– Maternal deaths
• Time specific– Weekly deaths
27
Total population in Madurai in 2015
28
No. of deaths in Madurai in 2015
29
Cause of death – cholera
30
Cholera specific death rate in Madurai in 2015
31
Proportional mortality rate
= X 100
32
Total population in Madurai in 2015
33
No. of deaths in Madurai in 2015
34
Total deaths
35
Cause of death – cholera
36
Proportional mortality rate of cholera
37
Total population (MYP)
Total deaths – all causes
Cholera deaths
CDR
Specific DR
PMR
38
Case fatality rate
CFR = X 100
39
Total no. of cholera cases
40
No. of people died due to cholera
41
Total no. of cholera cases
42
Survival rate
• Used in research studies• Like cancer therapy or survival
X 100
43
What is standardization?
You: My salary has doubled this month
Ur friend: My salary has also doubled
44
What is standardization?
¥. 1 Lakh = Rs. 10 Lakh¥. 2 Lakh = Rs. 20 Lakh
Gain = Rs. 10 Lakh
Rs. 1 LakhRs. 2 Lakh
Gain = Rs. 1 Lakh
45
What is standardization?
Rs. 1 Lakh = $ 1,500 ¥. 1 Lakh = $ 15,000Rs. 2 Lakh = $ 3,000 ¥. 2 Lakh = $ 30,000Gain = $ 1,500 Gain = $ 15,000
46
What is standardization?
You: My salary has doubled this month
Ur friend: My salary has also doubled
47
Direct standardization
48
Crude ratesMadurai Population Deaths Death rate per
10000-64 53,500 446 8.3
Chennai Population Deaths Death rate per 1000
0-64 92,000 850 9.2
49
Age specific ratesMadurai Population Deaths Death rate per
10000-24 21,500 123 5.7
25-64 32,000 323 10.0
Chennai Population Deaths Death rate per 1000
0-24 32,000 150 4.625-64 60,000 700 11.6
50
Standard population
Standard Population
0-24 156,000
25-64 45,000
51
Standardization for MaduraiStandard Population Madurai
ratesExpected
deaths0-24 156,000 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
∂
∂ ∂ ∂
52
Standardization for ChennaiStandard Population Chennai
ratesExpected
deaths0-24 156,000 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
∂
∂ ∂ ∂
53
Standardized ratesMadurai Population Deaths CDR per
1000Std. DR
per 10000-64 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
54
Indirect standardization
55
Standardized mortality ratio
Age National death rate per 1000
25-34 3
35-44 5
45-54 8
55-64 25
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
57
Standardized mortality ratioAge National
rateDoctor
populationObserved
deathsExpected
deaths25-34 3 300 * 0.935-44 5 400 * 2.045-54 8 200 * 1.655-64 25 100 * 2.5Total 1000 9.0 7.0
58
Standardized mortality ratio
SMR = X 100
SMR = 9/7 X 100 = 129
It means doctors experience 29% more mortality than the general population
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
60
MEASUREMENT OF MORBIDITY
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)
62
Incidence (நடக்குறது)
X 1000
63
Incidence – example
JANUARY 1, 2016 DECEMBER 31, 2016
64
Special incidence rates
• Attack rate• Secondary attack rate
65
Uses of incidence rate
• For taking action to control disease• More suited for acute or infectious conditions• For research
66
Example of use of incidence
This news article is giving only the numerators,Without denominator, it is hard to place much importance
67
Example of use of incidence
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
69
Prevalence (இருக்குறது)
X 1000
70
Types of prevalence
• Point prevalence • Period prevalence
71
Point prevalence – example
JANUARY 1, 2016 DECEMBER 31, 2016
72
Period prevalence – example
JANUARY 1, 2016 DECEMBER 31, 2016
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
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
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
76
Example of use of prevalence
77
Example of use of prevalence
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
79
Relation between incidence & prevalence
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
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
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
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 failedb) Reporting of dengue cases has improvedc) Treatment for dengue has failedd) Public awareness on dengue has increased
84
Review 2
• Prevalence of Diabetes is increasing every year in India. This could mean all EXCEPT,
a) Incidence of DM is increasingb) Reporting of diabetes has increasedc) Diabetic patients are surviving longer due to better
treatmentd) Public awareness on diabetes has increasede) None of the above
85
Review 3
• Examples of a disease with high incidence but low prevalence include (multiple options)
a) Acute respiratory infectionb) Acute diarrhoea c) TBd) Leprosy
86
Review 4
• Examples of a disease with low incidence but high prevalence include (multiple options)
a) Acute respiratory infectionb) Acute diarrhoea c) TBd) Leprosy
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 workb) The programme worked c) Data not sufficient
88
Review 6
• Disadvantages of crude death rate include (multiple options)
a) Simple measureb) Influenced by the age compositionc) Not comparable between countriesd) All of the above
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
90
Review 8
• Standardized rates can be calculated for
a) Age b) Sex c) Race d) Literacy ratee) All the above
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.
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 arrestd) Rupture of myocardium
93
Review 11
• Mid year population is not the denominator for (multiple options)
a) Age specific death rateb) Cause specific death ratec) Crude death rated) Proportional mortality ratee) Case fatality rate
THANK YOU
You can find this presentation on Email your queries to [email protected]