Disability Adjusted Life Years

Moderator – Dr. Abhishek V. Raut

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Plan of the presentationVarious 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.

“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.

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?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.

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? DALY = YLL + YLD YLL = N * L

where:

N = number of deaths

L = standard life expectancy at age of death in years

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

82.5 YEARS

NO DISABILITY

Life expectancy For the normal life

Degree of disability

Normal life

Degree of disability & Quality of 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

82.5 YEARS

Lifetime lost due to premature mortality.

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

82.5 YEARS

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 –

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.”

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

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.

Age weightingLife 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 is a modification of QALY. (is a negative QALY). Both concepts combine information about length of life and

quality of life.

QALY DALY QALYs are years of healthy life lived. DALYs are years of healthy life lost.

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

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◦ 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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SummaryThe 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 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.