Comparison of mortality rates are important in public health. hence standardisation is of important value in public health

1. MORTALITY RATES AND
STANDARDIZATION
Presenter : Dr. Vaishnavi C
Post graduate, MD community medicine
M S Ramaiah medical college, Bangalore5/20/2016 1

2. CONTENTS
 Introduction
 Frequency measures- Rates, ratios and proportions
 Mortality rates
 Definition
 Parts
 Types of mortality rates
 Relevance of mortality rates in public health
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3. CONTENTS
 Comparing mortality data
 Standardization of mortality rates
 Definition
 Types
 Example
 Issues of standardization – advantages and disadvantages
 Summary
 References
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4. Introduction
• Statistics are used to summarize the data collected
 describe risk
 make comparisons
 identify high-risk groups
 develop hypotheses about the cause(s) of disease
• Most common – frequency measures
 Rates, ratios and proportions
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5. Frequency Measures
• Ratios –
compares the occurrence of a variable in two different groups
Eg:
No. of male children attending a immunization clinic
No. of female children attending a immunization clinic
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6. Frequency Measures
• Proportions:
A proportion is a ratio which indicates the relation in
magnitude of a part of the whole
Eg:
No. Of male children attending the immunization clinic
Total number of children attending the immunization clinic
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7. Frequency Measures
• Rates:
 Type of frequency measure used with two-category
variables
 Measure the occurrence of an event in a population over
time
 Reflect groupings of people based on time, place and
person.
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8. Frequency Measures
• Comprises the following – numerator, denominator, time
specification and multiplier.
• Usually expressed as per 1000 or 1, 00,000 according to
convenience or convention to avoid fractions.
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9. Frequency Measures
• a ratio to compare two independent groups
• a proportion to compare one group with a larger one to
which it belongs
• a rate to measure an event in a population over time
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10. Categories of rates:
 Crude rates
 Specific rates
 Standardized rates
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11. Mortality rates
• Mortality rates measure the frequency of occurrence of death
in a defined population during a specified interval
• Difference in the risk of dying from a disease
• Can serve as measures of disease severity
• Serve as surrogates for incidence rates when the disease being
studied is severe and lethal one.
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12. Mortality rates
• Essential components of death rates:
• A population group exposed to the risk of death
• A time period
• The number of deaths occurring in the population during that
time period
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13. Types of mortality rates
Crude Death Rate:
Number of deaths in an area in a year per 1000 population
counted at midyear
Total No. of Deaths from all causes in 1 year X 1000
No. of persons in the population at mid year
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14. Mortality rates
Specific mortality rates:
• To calculate the rate specifically for a group eg. Age, sex,
ethnic groups
Age specific mortality rate :
No. of deaths among children < 10 years in one year X 1000
No. of children in the population < 10 years of age at mid year
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15. Mortality rates
• Eg:
Annual mortality rate from leukemia
in children < 10 years of age
= No. of deaths from leukemia in one year in children < 10 years
No. of children in the population < 10 years at mid year
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16. Mortality rates
Case Fatality Rates:
• What percentage of people who have a certain disease die
within a certain time after their disease was diagnosed
• It is the measure of disease severity
No. of individuals dying during a specified
period of time after disease onset or diagnosis X 100
No. of individuals with the specified disease at that particular
time
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17. Mortality rates
Proportional Mortality Rate:
• Represents the no. of deaths due to particular cause per 100/
1000 total deaths
• Expressed as percentage
No. of deaths from a specific cause X 100
Total No. of deaths in the population
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18. Example:
Assume a population of 1,00,000 of whom, 20 are sick with the
disease X and in that year 18 die from the disease X and total
deaths from all causes is 36.
Crude Death rate = 36 per 1 lakh population
Case fatality rate = 18/20 X 100 = 90%
Proportional mortality rate = 18/36 x 100= 50%
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19. Relevance of mortality rates in public health
• Single indicator which can signal a broad range of health
problems
• Clearly an index of the severity of a disease from both clinical
and public health stand points
• Also be used as an index of the risk the disease
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20. Relevance of mortality rates in public health
Are good reflection of incidence rates under 2 conditions:
• When the case fatality rate is high
• When the duration of disease is short
Eg: Ca. Pancreas is a highly lethal disease and death generally
occurs within months of diagnosis. Hence mortality rates from
ca pancreas can be taken as the incidence of the disease.
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21. Limitations of mortality data:
• Incomplete reporting of deaths
• Lack of accuracy - inaccuracies in the recording of age and
cause of death
• Lack of uniformity
• Choosing a single cause of death
• Diseases with low fatality
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22. Comparing mortality in different population
• Important for the evaluation of community health status
• Used to compare two or more populations or one population in
different time periods
• populations may differ in regard to many characteristics & so
comparisons of crude rates can be misleading
• Differences in determinants can distort comparisons between
populations
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23. Advantages Disadvantages
Crude Death Rate  Actual summary rates
 Readily calculable
 Since populations vary
in composition (e.g.,
age), differences in
crude rates difficult to
interpret
Specific Rates  Homogenous
subgroups
 Detailed rates useful
for
epidemiologic and public
health purposes
 Cumbersome to
compare many
subgroups of two or
more populations
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24. Comparing mortality in different population
Two criteria:
• Rates should relate the number of events to
the population at risk
• Because many health outcomes vary by
age, the effect of the population’s age
distribution must be taken into account
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25. Several techniques for adjusting age-specific rates:
• Direct and indirect standardization
• The comparative mortality index
• Equivalent average death rates
• Life table rates
• Yerushalmy’s index
• Cumulative death rates
• Regression analysis & multivariate techniques
Source: WHO: Age standardization of rates
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26. Standardization of rates
• Set of techniques used to remove as far as possible the effects
of differences in age or other confounding variables when
comparing two or more variables
• Age and sex are two of the most common variables used for
standardization - called standardized rates
• Involves taking weighted averages of the stratum-specific
outcome measures
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27. Standardization of rates
• A standard is a set of weights that is used in taking weighted
average
Eg: if the only stratification variable is age, a standard might be
the amount of person-time or number of persons in a standard
population that fall into each of the age categories
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28. Standardization of rates
2 types :
 Direct standardization
 Indirect standardization
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29. Direct standardization
• To compare health outcomes among populations that may have
different age distributions
• Used when age specific rates of disease are known for the
populations being compared.
• A standard population is used in order to eliminate the effects
of any differences in age between the two or more populations
being compared
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30. Standard population
 Defined as one for which the numbers in each age and sex
group are known.
 "Artificial populations" with fictitious age structures
 uniform basis for the calculation of comparable measures for
the respective reference population
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31. Choice of standard population: considerations
• When several different populations are being compared, a
‘pooled’ standard minimizes the variance of the adjusted rates
• In examining trends, an appropriate standard is one that
reflects the average structure of the population over the time
period
• The standard should be similar to the population of interest
• It should not change frequently (all historic data would need to
be recomputed)
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32. One of the following is used for a standard age distribution:
• The distribution of one of the populations being compared
• An independent standard, e.g. national population in an
arbitrarily chosen year
• A distribution constructed by combining the populations, e.g.
by averaging or totalling
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33. Steps in calculating age adjusted rate:
Step 1:
A hypothetical “standard population” is created
Step 2:
The age-specific rates of the population whose crude death rate
has to be standardized is applied to the standard population
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34. Steps in calculating age adjusted rate:
Step 3: For each age group an expected number of deaths in the
standard population is obtained.
Step 4: The expected number of deaths are added together for all
age groups to get the total expected deaths.
Step 5: Divide the total expected deaths by the total of the
standard population, which yields the standardized or age-
adjusted rate.
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35. Age
group
s
Population
A
No. Of
deaths
in each
age
group
Age
specific
death
rate
Age
groups
Populati
on B
No. Of
deaths
in each
age
group
Age
specific
death
rate
B1 A1 B2 A2
CDR = A1/B1 CDR =A2/B2
Age
groups
Std
populati
on
Age
specific
death
rates
Expected
deaths
Age
groups
Std
populati
on
Age
specific
death
rates
Expected
deaths
C1 D1 C1 D2
ADR1 = D1/C1 ADR2 = D2/C1

36. Direct Standardization
• Standardised rate :
No. of estimated events for a community X 100
Total population of the community
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37. Example 1:
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Population A Population B
No. of deaths 862 1130
Total population 900000 800000
Crude mortality rate
(per 1,00,000
population)
96 142

38. Example 1:
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Population A Population B
No. of deaths 862 1130
Total population 900000 800000
Crude mortality rate
(per 1,00,000
population)
96 142

39. Age group Population A Population B
Total
number
No. of
deaths
Death
rates/1
00000
Total
number
No. of
deaths
Death
rates/10
0000
30-49 500000 60 12 400000 30 8
50-69 300000 396 132 200000 400 200
>70 100000 406 406 200000 700 350
Total 900000 862 96 800000 1130 142
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40. Standard population
Age Population
30-49 900000
50-69 500000
>70 300000
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41. 5/20/2016 42
Age group Standard
populatio
n
Age
specific
mortality
rates –
Pop- A
Expected
number of
deaths I
Age
specific
mortality
rates-
pop- B
Expected
number of
deaths II
30-49 900000 12 108 8 72
50-69 500000 132 660 200 1000
>70 300000 406 1218 350 1050
Total 1700000 96 1986 142 2122

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Age group Standard
populatio
n
Age
specific
mortality
rates –
Pop- A
Expected
number of
deaths I
Age
specific
mortality
rates-
pop- B
Expected
number of
deaths II
30-49 900000 12 108 8 72
50-69 500000 132 660 200 1000
>70 300000 406 1218 350 1050
Total 1700000 96 1986 142 2122

43. • Age adjusted rates:
No. of expected deaths X 100000
Total standard population
• Population A = 1986 /1700000= 117 per 100000 population
• Population B = 2122/1700000= 125 per 100000 population
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44. Example 2:
Age Total subjects Cases Controls
No Heavy
smokers
% No Heavy
smokers
%
40-49 500 400 200 50 100 50 50
50-59 500 100 10 10 400 40 10
Total 1000 500 210 42 500 90 18
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45. Age adjustments are carried out
• By combining number of subjects in both the age groups
(500+500 = 1000) to create a standard population
• Applying the observed age-specific proportions of heavy
smokers to the same standard population
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46. 5/20/2016 47
Age Subjects Expected number of heavy smokers
Cases controls
40-49 500 500X50/ 100 = 250 500X50/100 = 250
50-59 500 500X 10/100 = 50 500X 10/100 = 50
Total 1000 300 300
Standardized rates
Cases= 300X 100/1000 = 30
Controls = 300X 100/1000 =30

47. Direct Standardization
• Direct method requires the knowledge of age specific rates of
the events under comparison for each of the communities as
well as the standard population age structure.
• Sometimes, the above data may not be available or the
population in different age or sex groups or may be too small
resulting in large fluctuating of the age specific rates through
the presence of only a few events
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48. Indirect method of standardization
• Requires the knowledge of the age and sex structure of the
population as well as the age and sex specific rates of events
under consideration for the standard population
• Used when the number of deaths for each age specific stratum
is not available
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49. Indirect method of standardization
• Steps:
• Step 1: Choose a reference or standard population.
• Step 2: Calculate the observed number of deaths in the
population (s) of interest
• Step 3: Apply the age-specific mortality rates from the chosen
reference population to the population(s) of interest.
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50. Indirect method of standardization
• Step 4: Multiply the number of people in each age group of the
population(s) of interest by the age-specific mortality rate in
the comparable age group of the reference population.
• Step 5: Sum the total number of expected deaths for each
population of interest.
• Step 6: Divide the total number of observed deaths of the
population(s) of interest by the expected deaths
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51. Standardized Mortality Ratio (SMR):
• The simplest and most useful form of indirect standardization
• Ratio of the total number of deaths that occur in the study
group to the number of deaths that would have been expected
to occur if that study group had experienced the death rates of
the standard population
SMR = Observed Deaths X 100
Expected Deaths
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52. 5/20/2016 53
Age groups Population A Observed No of
deaths in each
age group
(obs1)
Population B Observed No of
deaths in each
age group
(obs2)
A1 B1
CDR1 = Obs
1/A1
CDR2 =
Obs 2/B1
Age groups Std Age
specific
death rates
S
Populatio
n A
Expected
deaths in
each group
Population B Expected
deaths in
each group
E1 = S* A1 E2 = S*B1
SMR 1 = Obs 1/ E1 SMR 2 = Obs 2/ E2

53. Example 1
• In a population of 5,34,533 miners in a country, 436 deaths
from tuberculosis occurred in 2000.
• The question of interest is whether this mortality experience
from TB is greater than, less than or about the same as that
expected from the general population
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54. 5/20/2016 55
Age (yr) Estimated
population of
miners
Observed deaths
from TB in
miners
Death
rate/1,00,000 for
TB in general
population
20-24 74598 10 12.26
25-29 85077 20 16.12
30-34 80845 22 21.54
35-44 148870 98 33.96
45-54 102649 174 56.82
55-59 42494 112 75.23
Total 534533 436

55. 5/20/2016 56
Age (yr) Estimated
population of
miners
Observed deaths
from TB in
miners
Death
rate/1,00,000 for
TB in general
population
20-24 74598 10 12.26
25-29 85077 20 16.12
30-34 80845 22 21.54
35-44 148870 98 33.96
45-54 102649 174 56.82
55-59 42494 112 75.23
Total 534533 436
Std population

56. 5/20/2016 57
Age (yr) Estimated
population of
miners
Death
rate/1,00,000 for
TB in general
population
Expected deaths
from TB in
miners
20-24 74598 12.26 9.14
25-29 85077 16.12 13.71
30-34 80845 21.54 17.41
35-44 148870 33.96 50.55
45-54 102649 56.82 58.32
55-59 42494 75.23 31.96
Total 534533 181.09

57. SMR = 436 / 181.09 X 100
= 241
• SMR = 100 - observed death is same as expected death.
• SMR < 100 - observed death is less than expected death.
• SMR > 100 - observed death is more than expected death.
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58. Example: 2
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Age Population Std population –
age & sex specific
death rates
Estimated deaths
Males Females Males Females Males Females
0-4 734 685 58.3 70.2 42.8 48.1
5-14 1494 1311 4.5 5.3 6.7 6.9
15-19 471 352 2.1 4.2 1.0 1.5
20-24 397 399 3.9 5.5 1.5 2.2
25-29 386 362 3.7 5.5 1.4 2.0
30-34 339 327 4.1 6.4 1.4 2.1
35-39 293 239 6.5 6.1 1.9 1.5
Total 4114 3675 56.7 64.3

59. • Index death rate for the population =
total estimated events X 1000
total population
Index rate = 121/ 7789 X 1000
= 15.5
Standardising factor = Overall death rate of standard population /
Index rate
= 23.91 / 15.5
= 1.54
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60. • Standardised death rate for the community;
Observed rate X standardizing factor
= 12.7 X 1.54
= 19.6
Crude – 12.7
Standardised rate = 19.6
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61. Advantages of standardization:
• Summarizes stratum specific rates
• Unconfounded comparison of population
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62. Issues in the use of standardisation:
• Standardised rates are used for the comparison of two or more
populations; they represent a weighted average of the age
specific rates taken from a 'standard population' and are not
actual rates.
• The direct method of standardisation requires that the age-
specific rates for all populations being studied are available
and that a standard population is defined.
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63. Issues in the use of standardisation:
• The indirect method of standardisation requires the total
number of cases
• As the choice of a standard population will affect the
comparison between populations, it should always be stated
clearly which standard population has been applied.
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64. Summary
• Most common statistical measures – Rates, ratios, proportions
• Mortality rates – relevance in public health
• Crude death rates are easy to calculate but distort the
comparisons between population
• Hence standardization is used to enable comparisons
• 2 types – direct and indirect
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65. Summary
Direct Indirect
Target Population Group specific rates Group population
sizes
Standard
Population
Group population
sizes
Group specific rates
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66. Summary
Advantages Disadvantages
Summarizes stratum specific
rates
Fictitious values
Unconfounded comparison of
population
Values depend on the choice of
standard population
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67. References
• Gordis L. Epidemiology. 4thed. Philadelphia (USA): Elsevier
Saunders; 2009. p.
• RothmanKJ, Greenlands S, lash TL. Modern Epidemiology. 3rd ed.
Philadelphia (USA): Lippincot Williams and Wilkins. 2008. P.
• Park K. Textbook of Preventive and Social Medicine. 22nd ed.
Jabalpur (India): Banarasidas Bhanot; 2013.p.
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68. References
• Detels R, Beaglehole R, Lansang MA, Gulliford M. Oxford
Textbook of Public Health. 2nd ed. United Kingdom: Oxford
University press;2001. p.
• Hennekens CH, Buring JE. Epidemiology in medicine. 1st ed.
Boston: Little, Brown and Company; 1987.
• Rao NSN, Murthy NS. Applied Statistics in Health sciences. 2nd ed.
New Delhi (India): Jaypee Brothers Medical Publishers; 2010.
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69. References
• Age standardization of rates: A new WHO standard. World Health
Organisation [online] 2001 [cited on 2016 May 1];Available from:
URL: http://www.who.int/healthinfo/paper31.pdf
• The use of epidemiological tools in conflict affected populations:
open access educational resources for policymakers. World Health
Organisation [online] 2002 [cited on 2016 Apr 24]; Available from:
URL:http://www.who.int/hac/techguidance/tools/disrupted_sectors/a
dhsm_mod14_en.pdf
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70. References
• Standardization of rates and ratios. Concepts and basic methods for
deriving measures that are comparable across populations that differ
in age and other demographic variables [Online] [ cited on 2016 Apr
20];Available from: URL:
http://www.epidemiolog.net/evolving/Standardization.pdf
• West MD, Kanchanaraksa S. The Direct and Indirect Methods of
Adjustment. John Hopkins School of Public Health [online] [cited
on 2016 Apr 23]; Available from: URL:
http://ocw.jhsph.edu/courses/fundepi/PDFs/Lecture7.pdf
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71. References
• Standardization of rates. Boston University School of Public Health
[online] 2006 [Cited 2016 Apr 21]; Available from: URL:
http://sphweb.bumc.bu.edu/otlt/MPH-
Modules/PH/Woburn/Woburn8.html
• Curtin LR, Klein RJ. Direct Standardization (Age-Adjusted Death
Rates). Healthy People 2000. CDC [Online] 1995 [Cited on 2016
Apr 24]; Available from: URL:
www.cdc.gov/nchs/data/statnt/statnt06rv.pdf
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72. THANK YOU
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