measures of disease and morbidity,disability adjusted life years(DALY) Years lost due to disease(YLD), measures of mortality

1. MEASURES ON
DISEASE AND
MORBIDITY
• Dr ADiL SHAiK

3. Disability-Adjusted Life Year
(DALY)
Quantifying the Burden of Disease from mortality and morbidity
Definition
• One DALY can be thought of as one lost year of "healthy" life. The sum of these
DALYs across the population, or the burden of disease, can be thought of as a
measurement of the gap between current health status and an ideal health
situation where the entire population lives to an advanced age, free of disease and
disability.
• DALYs for a disease or health condition are calculated as the sum of the Years of Life
Lost (YLL) due to premature mortality in the population and the Years Lost due to
Disability (YLD) for people living with the health condition or its consequences:

4. Calculation
• The YLL basically correspond to the number of
deaths multiplied by the standard life
expectancy at the age at which death occurs.
The basic formula for YLL (without yet
including other social preferences discussed
below), is the following for a given cause, age
and sex:
where:
• N = number of deaths
• L = standard life expectancy at age of death in
years

5. Prevalence YLD
• Prevalence YLD
• The recent GBD 2010 study published by IHME in
December 2012 used an updated life expectancy
standard for the calculation of YLL and based the
YLD calculation on prevalence rather than
incidence:
• where:
• P = number of prevalent cases
• DW = disability weight

6. Measurements of Morbidity
Morbidity:
• Morbidity has been defined as “any
departure, subjective or objective, from a
state of physiological well being”
• The term is used equivalent to such terms as
sickness, illness, disability etc.

7. Data on Morbidity; why it is useful:
Many diseases with a low case fatality e.g mental
illnesses, musculoskeletal diseases, rheumatoid
arthritis, chicken pox and mumps. In this situation,
data on morbidity (Illness) are more useful than
mortality rates.

8. Incidence
Incidence
• Incidence rate is defined as “ the number of NEW cases
occurring in a defined population during a specified
of time.
Incidence
number of NEW cases of specific disease during given time period x 1000
population at risk during that period

9. For example: If there had been 500 new cases of
an illness in a population of 30,000 in a year, the
incidence rate would be:
500/30,000 X 1000
= 16.7 per 1000
Note: the incidence rate must include the unit of
time used in the final expression. If you wrote 16.7
per 1000, this would be inadequate. The correct
expression is 16.7 per 1000 per year.

10. Special Incidence rates
Special incidence rates
• Attack rate
An attack rate is an incidence rate (usually
expressed as a percent), used only when the
population is exposed to risk for a limited period
of time such as during epidemic.
• Secondary attack rate
The number of exposed person developing the
disease within the range of the incubation period
following exposure to a primary case.

11. Attack rate
number of cases of specific disease during given time period x 1000
population at risk during that period

12. Secondary attack rate
Suppose there is a family of 6 consisting of 2 parents
(already immune) and 4 children who are susceptible to
a specific disease, say Measles. There occurs a primary
case and with in a short time 2 secondary cases among
the remaining children. The secondary attack rate is
SAR = No of exp ppl developing disease within range of
I.P X 100
Total no of exp ppl
2/3 X 100 = 66 per 100.
Here a primary case is excluded from both numerator
and denominator.

13. In a population of 1000, measles immunization coverage is 60%, 1 child
(Primary case) goes out of station and come back with measles from which 20
(secondary cases) more children get measles. Calculate secondary attack rate.
 Immunised children = 60% = 600
 Non Immunised children 40 % = 400
 Primary case will be excluded from denominator
SAR = No of exposed people developing disease within range of IP X 100
----------------------------------------------------------------------
Total no of exposed people
= 20/399 X 100 = 5% or 5 per 100

14. Uses of incidence rate:
The incidence rate, as a health status indicator, is
useful for taking action,
• To control a disease
• For research into etiology and pathogenesis,
distribution of disease and efficacy of preventive
and therapeutic measures.
For instance if the incidence rate is increasing it
might indicate failure or ineffectiveness of the
current control programs. And suggest the need
for a new disease control program.

15. Prevalence
• The term “disease prevalence” refers specifically to
ALL CURRENT CASES (old and new) existing at a
given point in time or over a period of time in a
given population.
Prevalence is of two types
• Point Prevalence
• Period prevalence

16. Point Prevalence:
It is defined as number of all current cases (old and new)
of a disease at one point of time, in relation to a defined
population. The point in a point prevalence, may for all
practical purposes consists of a day, several days or even
a few weeks depending upon the time it takes to
examine the population sample.
PP=
no of all cases (old & new) of a specified disease existing at a given point in time X 100
Estimated population at the same point in time

17. Period Prevalence:
A less commonly used measure of prevalence is period
prevalence. It measures the frequency of all current
cases (old and new) existing during a defined period of
time. e.g (Annual Prevalence) expressed in relation to
defined population.
It includes cases arises before but extending into or
through to the year as well as those cases arising during
the year.
Period Prevalence=
no of all cases (old & new) of a specified disease during a given period of time interval X 100
Estimated mid interval population at risk

18. Uses of prevalence:
• Prevalence helps to estimate the magnitude
of health/disease problem in the community,
and identify potential high-risk population
• Prevalence rates are specially useful for
administrative and planning purposes e.g.
hospital beds, manpower needs,
rehabilitation facilities etc..

19. Measures of Mortality
• Crude Death Rates
• Age-Specific Death Rates
• Life Table Estimates
• Life expectancy
• Cause-Specific Death Rates

20. Crude Death Rate
• Crude Death Rate (CDR)
• Number of deaths in a given year per 1000
mid-year population
Number of deaths in that year/ mid Year
population *1000

21. Age Specific Death Rates (ASDR)
• Number of deaths per year in a specific age
(group) per 1000 persons in the age group
• Where Da =Number of deaths in age group a
Pa= Midyear population in age group a
• Da/Pa*1000

22. Cause Specific Death Rates
Cause Specific Death Rates:
Number of deaths attributable to a particular
cause C divided by population at risk usually
expressed in deaths per 100,000
Dc/P *100k

23. Life Table
• The Life Table
A powerful demographic tool used to simulate
the lifetime mortality experience of a population,
by taking that population’s age-specific death
rates and applying them to a hypothetical
population of 100,000 people born at the same
time

24. Life Expectancy
• Life Expectancy at Birth
Average number of years lived among a cohort of
births experiencing deaths at each year of age
throughout their remaining life-time according to
a specific schedule of age specific mortality rates
• Note: This measure of mortality is independent of
the age structure of the population

25. THANK YOU