DALYs

Report
Moderator – Dr. Abhishek V. Raut
Plan of the presentation
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Various indicators Of Disability
What are DALYs?
What can they be used for?
How are DALYs constructed and calculated?
Relation between QALY and DALY.
Problems with DALYs approach
What is Global Burden of Disease Study ?
Summary
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Indicators Of Disability

In 1940, Dempsey's concept of using “Years Of Life Lost” was
used as a metric for assessing the health burden associated with
deaths occurring prior to an ‘ideal’ life span of 65 years.
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“Life Tables” approach was a subsequent measure incorporating
non-fatal health outcomes using a life-table approach which
quantified time lived with disease or injury lost according to
severity of disability , pain or distress.

“Sullivan’s index” is computed by subtracting from life
expectancy, the probable duration of bed disability and inability
to perform major activities, is one of the advanced indicators.
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Concept of DALY was first presented in the “World Development
Report; 1993” by the World Bank and gained wider attention and
interest.
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What are DALYs?
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DALYs = Disability Adjusted Life Years is a measure of
disease on the defined population and the effectiveness
of interventions.
A common measurement unit for morbidity and
mortality
Facilitates comparisons of all types of health states and
outcomes
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Possible uses of DALYs
DALYs can be used in three interrelated areas:
 For epidemiological surveillance of the total disease burden
(number of DALYs)
 To measure cost- effectiveness of interventions (cost per
avoided DALY)
 To decide what should be included in a country’s ‘core
services’ (the package of essential health care services).
The concept of DALYs thus provide information for
policy makers concerned with international health, the health
of developing countries, and national priority setting.
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How are DALYs constructed?

One DALY can be thought of as one lost year of "healthy" life.
The sum of these DALYs across the population, 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.
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A DALY is a health outcome that measures-
◦ the Years of Life Lost (YLL) due to premature mortality
in the population and
◦ the Years Lost due to Disability (YLD) for incident cases
of the health condition
◦ DALY = YLL + YLD
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How are DALYs constructed?
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DALY = YLL + YLD
 YLL = N * L
where:
N = number of deaths
L = standard life expectancy at age of death in years
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YLD = I * DW * L
where:
I = number of incident cases
DW = disability weight
L = average duration of the case until remission or death (years)
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DALYs due to living with disability
NO
DISABILITY
Degree
of
disability
Degree of disability & Quality of Life
Normal life
82.5YEARS
Life expectancy For the normal life
Example; a girl aged 5 & a victim of a mine explosion causing a below-knee
amputation, and she does not die but is rehabilitated to a health state with some
loss of physical functioning. Her loss is 77.5 years adjusted by a disability weight
i. If this weight is, say, 0.3, her loss is 0.3 x 77,5 = 23.3.
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DALYs due to early death
(Red area measures DALYs. Red + white is a normal life)
NO
DISABILITY
Lifetime
lost due to
premature
mortality.
82.5YEARS
Premature death from a myocardial infarction, say at age 50. This
patient’s loss is 33.5 years.(DALY= YLL= N *L ) No adjustment is made
for disability because the patient dies.
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DALYs due to disability and premature death
combined.
NO
DISABILITY
82.5YEARS
This graph shows a woman who lives with a disability, for instance deafness
from the age of 5 and dies prematurely at the age of 50.
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Calculation of DALYs
 The
calculation of DALYs of a woman who has been deaf
since she was 5 and dies when she is 50: ( Disability
weight of deafness is set at 0.33) :
 DALY = YLL + YLD
= (N*L) + (I*DW*L)
= (1 * 32.5) + (1* 0.33 * 45)
= 32.5 + 0.148
= 32.648
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How are disability adjustments made?
A disability weight is a weight factor that reflects the
severity of the disease on a scale from 0 (perfect health) to
1 (equivalent to death).
How to assign a disability weightings to life years  Diagnostic groups must be chosen and defined.
 Descriptions of those diagnostic groups are developed.
 The health states are assigned a disability weight to
indicate the relative severity of each health state.
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Method used for weighting disability
Disability weights are obtained by posing two different
Person Trade-Off (PTO) questions to expert panels –
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In PTO1 panellists are asked to compare the value of extended life
in people without disabilities with that in disabled people.
“If the panellist judges that 1000 healthy people would have an equal
claim on the resources as 8000 people with some severe disability, the
weight assigned to that particular disability is equal to 1 minus 1000
divided by 8000, or 0.875.”
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In PTO2 panellists are asked to value cures for different chronic
conditions relative to interventions that extend life.
“For instance, how many people cured of blindness does the
respondent consider equal to prolonging the lives of 1000 people? If
the response is 5000, the corresponding disability weight of blindness is
1000:5000 = 0.2.”
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Age weighting and Discounting

In addition to adjusting the value of life years with
disability weights, and choosing a particular life
expectancy, the value of a life year is modified by
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Discounting
The value of a life year now is set higher than the value of
future life years.
This is common practice when it comes to valuing material
goods. For instance, we may require 5000 Rs. in 10 years
time to compensate for a bank loan of 1000 Rs. today.
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Age weighting
Life years of children and old people are counted less.
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Age-weights
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The effect of age-weighs and discounting
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Calculating DALY score,
with age weighting and discounting.

Girl, 5 years old, with below-knee amputation
who lives until she is 82.5:
 DALYs= life years lived with disease (77.5) ×
disability weight (0.3) × age- weight (a1)×
discounting factor (d2)
 77.5 × 0.3 × a1 × d2
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QALYs and DALYs

QALY is defined as an adjustment of life expectancy that reduces
the overall life expectancy by amounts which reflect the existence
of chronic conditions causing impairment, disability or handicap.
 DALY QALY
is a modification of QALY. (is a negative
QALY).
DALY
 Both
concepts
combine
information
about
life and
 QALYs
are years
of healthy
life lived.
 DALYs
are length
years of of
healthy
life lost.
quality of life.
 QALYs multiply number of years
lived healthy by the ”quality” of those
years; is called “Quality adjustment”.
 DALYs multiply number of years lived
with disability by the ”quality” of those
years; is called ”Disability adjustment”.
 QALYs represent a gain and should be
maximised.
 DALYs represent a loss and should be
minimised.
 In the QALYs the scale goes in
opposite way: A quality weighting
(“utility”) of 1 indicates perfect health,
and 0 indicates no quality of life (death).
 In the DALY approach, the years are
disability weighted on a scale from zero,
which indicates perfect health (no
disability), to one which indicates death.
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Relation between QALYs and DALYs
DALYs = healthy years lost
QALYs = healthy years gained
NO
DISABILITY
82.5 YEARS
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PROBLEMS of the DALY approach
Is
it true?
Questions of the validity of the results
Is
it just?
Questions of the distribution between groups
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General problems of validity
 What
is “Quality of Life” or “Disability weighting of
life years”?
 Can quality of life be measured in a single and precise
number?
 Does the same health problem have equal impact on
different persons or groups?
 Is there a general agreement to underlying value
choices: discounting, age weighting and choice of life
expectancy
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Validity problems of the PTO protocol
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Lack of simplicity, difficult to understand even
for trained researchers in the field
 People participating in evaluation panels are
forced to adopt discriminatory positions on the
value of life of disabled people (all individuals
are equally valuable.
 The expert panel may not represent the values
of other people
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Justice
The DALY approach has been criticised for
discriminating
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the young
the elderly
future generations (future health benefits)
the disabled
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What is the Global Burden of Disease study?

The Global Burden of Disease Study is a
collaboration between WHO, the World Bank, and
Harvard School of Public Health.
 The aims of the study was to provide information and
projections about disease burden on a global scale.
 Combines information about loss of quality of life
with traditional epidemiological information on
mortality
 All health outcomes are expressed in DALYs
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Leading Causes of Burden of Diseases in 2004
and projections for 2030
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Summary
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The Global Burden of Disease study provides a quantitative
overview of the burden of disease world-wide, expressed in
DALYs.
The DALY combines traditional epidemiological
information on mortality with information about loss of
quality of life and several value choices.
The value choices, as well as the epidemiological data
underlying the study are heavily debated.
The critical aspects of the validity of DALYs and some
implications for distributive justice are always commented.
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References
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Summary Measures of Population Health. J.L. Murray, J. A. Salomon,
A.D Lopez. WHO Geneva. 2002.
Determining Health Expectancies. J M Robine, C Jagger, RM Suzman.
2003.
Murray CJL: Quantifying the burden of disease: the technical basis for
disability-adjusted life years. Bulletin of the World Health Organization
1994, 72:429–445.
Murray CJL and Lopez A.D: The utility of DALYs for public health
policy and research. Bulletin of the World Health Organization 1997,
75(4):377–381.
Murray, C. J., & Lopez, A. D. (1997). Global mortality, disability, and
the contribution of risk factors: Global Burden of Disease Study.
Lancet, 349(9063), 1436-1442.
S. Anand, K. Hanson, Disability- adjusted life years: a critical review.
Journal of Health Economics 16(1997) 685- 702
The Global Burden of Disease; 2004 update. WHO Geneva.
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