1. Disability Adjusted Life Years
Moderator – Dr. Abhishek V. Raut

2. Plan of the presentation
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

3. 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.

4. 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
The DALY approach is increasingly cited as a powerful tool for decision-makers in international health (Bobadilla et al 1994, Bobadilla 1996, Murray and Lopez 1996). It’s attractiveness lies in the fact that it combines information about mortality and morbidity in a single number. DALYs allow the losses due to disability and the losses due to premature death to be expressed in the same unit. Hence, DALYs facilitate comparisons of different (in theory all) types of health states or health outcomes. In particular, this makes it easier to include the burden caused by disability and chronic diseases in cost-effectiveness studies. For instance, with such an index in place, one could say, that the number of DALYs due to the premature death of one girl aged 5, equals the number of DALYs caused by three girls of the same age suffering a below- knee amputation.

5. 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.

6. 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
It is essential to understand what the DALY-concept measures and how it is constructed. The following three figures visualise how the burden of disease is measured for a 'standard' individual. Burden is measured along two dimensions: time lived with disability and time lost due to premature mortality.

7. 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
I = number of incident cases
DW = disability weight
L = average duration of the case until remission or death (years)
It is essential to understand what the DALY-concept measures and how it is constructed. The following three figures visualise how the burden of disease is measured for a 'standard' individual. Burden is measured along two dimensions: time lived with disability and time lost due to premature mortality.

8. DALYs due to living with disability
Degree of disability & Quality of Life NO
DISABILITY
Degree of disability
Normal life
82.5 YEARS
The x-axis shows life expectancy for the 'normal' life. The "standardised" maximum life span, 82.5 years for females and 80 years for males, is taken from the country with the highest life expectancy in the world: Japan. The y-axis shows degree of disability. The 'normal' life is quantified as the total area in the box, a combination of the number of years lived and the quality of life, or degree of disability. From this ideal state of the world it is possible to calculate the burden of disease caused by premature death or disability.
If for example a girl aged 5 happens to become 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 DALY loss could be depicted as the red area in the figure. 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.
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.

9. DALYs due to early death (Red area measures DALYs
DALYs due to early death (Red area measures DALYs. Red + white is a normal life) NO
DISABILITY
Lifetime lost due to premature mortality.
Premature death from a myocardial infarction, say at age 50, would produce the DALY-loss as depicted by the red area in the figure. This patient’s loss is 33.5 years. No adjustment is made for disability because the patient dies.
82.5 YEARS
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.

10. DALYs due to disability and premature death combined.NO
DISABILITY
This schematic illustration shows a woman who lives with a disability, for instance deafness from the age of 5 and dies prematurely at the age of 50.
The calculation of her DALY score would be as follows on the next slide:
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.

11. 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) = =
This example is, for didactic reasons, a simplified way of calculating DALY loss, omitting age-weighitng and discounting.

12. 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.
If, for instance, we want to find the burden of back ache, we must first define what we mean by back ache. Do we mean an incapacitating condition or do we mean a slight discomfort?
Only when the condition is defined and described will it be meaningful to ask how much this condition reduces the quality of life of the one carrying it.
How much should the value of a life year be adjusted for back ache? The disability weighting is the most difficult and controversial part of the DALY approach. We will come back to this.
Here we show how it is currently done.

13. 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 divided by 8000, or ”
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.”
The disability weights are derived from presumably representative answers to questions of the type: "how many outcomes of one kind (e.g. saving girls from premature death) do you consider equivalent in social value to y outcomes of another kind (below-knee amputation for girls who have suffered mine explosions)"? The method used to assess these social preferences from a representative sample of persons is a deliberative person-trade-off technique. [Murray, 1996 ; Nord, 1994; Nord, 1995 ]

14. 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 weighting
Life years of children and old people are counted less.
In the Global Burden of Disease approach, future burdens are discounted at a rate of 3% per year, and the value of the lifetime is weighted so that years of life in childhood and old age are counted less. These choices are explained and discussed in (Murray, 1996 ).
Discounting means that future gains and losses are counted less than if they had occurred today. This is common practice when it comes to valuing material goods. For instance, a bank may require 500 dollars in 10 years time to compensate for a loan of 100 dollars today. However, it is controversial whether if it is correct to apply discounting on human values. It has for instance been asked why future generations should be counted as less valuable.

15. Age-weights
Age weighting means that life years in young and old age are counted less.
This figure shows the relative value assigned to each year of life in the calculation of disease burden. Source:World Bank, The relative value of a life year is below one for children under 10, and for persons more than about 55 years of age. This implies that in the calculations, a life year lost for children is given less weight than a life year lost for adults below 55. The adjustments made, introduces (explicitly), a bias both against children and the elderly. In a defence of age-weights, Christopher Murray argues that there is a widespread preference for age weighting in most cultures (Murray, 1996), and, that on average, these preferences can be expressed as in the function given.

16. The effect of age-weighs and discounting
The result of combining the use of age weights and discounting future health benefits is shown in this figure.
As we see, the effects of age-weighting and discounting are additive.
In fact, if a 5 years old child dies, the resulting DALY score is lower than if a child of 10 year dies!

17. 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
Consider a five-year-old girl with a below-knee amputation after an accident with landmines. DALYs measure life years lost multiplied with a disability weight, multiplied with an age weight a1, multiplied with a discounting factor d2 (3 % for each year). The estimated DALY loss would be 77.5 ( ) years multiplied with 0.3 and adjusted with age weights and the discounting factor which give an estimated 10.5 disability adjusted life years lost.

18. QALYs and DALYs QALY DALY
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.
DALYs may be called a modification of QALYs Both approaches multiply number of years lived by the ”quality” of those years. This process is called ”Quality adjustment” in QALYs and ”Disability adjustment” in DALYs. The complementarily between the two concepts can be illustrated schematically:

19. Relation between QALYs and DALYs DALYs = healthy years lost QALYs = healthy years gainedNO
DISABILITY
Scematic illustration of the complementarity between QALYs and DALYs. QALYs are years of healthy life lived - DALYs are years of healthy life lost.
Whereas DALYs represent a loss and should be minimised, QALYs represent a gain and should be maximised.
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.
In the QALY approach, the scale goes the opposite way: A quality weighting (sometimes called “utility”) of 1 indicates perfect health, whereas 0 indicates no quality of life, and is synonymous to death.
( Age weighting and discounting factors are not included in this illustration).
82.5 YEARS

20. PROBLEMS of the DALY approach
Is it true?
Questions of the validity of the results
Is it just?
Questions of the distribution between groups
Some critical articles on the DALY approach have questioned both the validity of the results (Cooper, 1998) as well as the underlying value-judgements (Anand, 1997, Arnesen and Nord 1999). In the Journal of Health Economics Anand and Hanson argues that: "the conceptual and technical basis for disability-adjusted life years is flawed, and that the assumptions and value judgements underlying it are open to serious question.” (Anand, 1997). In particular, the implications for resource allocation and the just distribution of health benefits needs to be scrutinised.

21. 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
The most difficult part of any approach combining data on quality of life and length of life, is how to measure quality of life. How should one value health states numerically on a scale of zero to one? Many philosophical questions as well as questions regarding the limits of natural sciences are aroused.
The first requirement of a valid measurement is that one know what one is measuring. The concept of quality of life is, however, vaguely defined, and different people as well as different cultures may have very different opinions of the main elements of a good life.

22. 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
The Person Trade-off questions are difficult to understand, even for trained researchers in the field.
Through the imposition of consistency between substantially different questions, people participating in evaluation panels are forced to adopt discriminatory positions on the value of life of disabled people. In as much as the disability weightings do not correspond to a clear preference but are the results of forced compromise, they must be seen basically as artefacts.(Arnesen and Nord 1999)
A general question regards who should be asked to perform the valuations, whose values should count?
Lately, the WHO has signalized that they will change the approach of disability weighting in later versions of the Global Burden of Disase studies.

23. Justice The DALY approach has been criticised for discriminating
the young
the elderly
future generations (future health benefits)
the disabled
The approach has been criticized for violating the principle of treating people as equals. In the following these concerns are examined.

24. 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
The Global Burden of Disease Study is a collaboration between WHO, the World Bank, and Harvard School of Public Health. (Murray, 1996 ) The aims of the study was to provide information and projections about disease burden on a global scale. The method used has been described as a “meta-synthesis” of available information. (Murray, 1996 ).

25. Possible use of the Global Burden of Disease Study
Epidemiological surveillance of trends across borders and over time
Projections for future burden of disease
Basis of information for decision-making on priorities in health research and health policy
The main results from the Global Burden of Disease Study where first published for the World Bank report of 1993, and the latest complete and validated results were published in a series of four articles in (Murray, 1997) The following table shows the leading causes of world-wide lost DALYs for both sexes in 1990 and the projections for 2020.

26. Leading Causes of Burden of Diseases in 2004 and projections for 2030

27. Summary
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.

28. References
Summary Measures of Population Health. J.L. Murray, J. A. Salomon, A.D Lopez. WHO Geneva
Determining Health Expectancies. J M Robine, C Jagger, RM Suzman
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),
S. Anand, K. Hanson, Disability- adjusted life years: a critical review. Journal of Health Economics 16(1997)
The Global Burden of Disease; 2004 update. WHO Geneva.