23. 12
Properties of Proportions
p takes on values between 0 and 1
(p is a fraction)
p has no units
p may be multiplied by a
constant kWhere k is a number
such as 100, 1,000, or 100,000
24.
25.
26. Types of Mortality Rates/Ratio
• annual death rate
• crude death rates
• infant mortality rates (ratio)
• neonatal mortality rates
• postneonatal mortality rates
• perinatal mortality rates
• fetal death rates
• fetal death ratios
• abortion rates
• maternal mortality rates
• adjusted mortality rates
• standardized mortality ratio
• specific death rates
• proportionate mortality rate- case fatality rate
• mortality crossover – mortality time trends
Your Assignment:
familiarize yourself
with the definitions
of these terms
27. Three Levels of Rates
• Crude rates
• Specific rates/ratios
• Adjusted rates
28.
29. Crude Death Rates
• Does NOT account for differences of
age, sex, etc. in any aspect of death
• Info needed:
total deaths
total population
a given period of time
41. More Convenient:
Summarize an entire situation with a single number calculated
for each subpopulation, a number that adjusts for difference
in composition
Two Ways:
1. Direct method of standardization
2. Indirect method of standardization
42. Direct Method of Standardization:
Step 1:
Select the standard population.
Step 2:
compute the expected events that would result if
,instead of having different age distributions, all populations were
to have same standard age structure
Step 3:
Compute the adjusted rate as total expected events in the
group divided by the total standard population
43. Adjusted Death Rates
Age Adjusted Rates
• Direct Method
What data available for you for direct method?
46. Indirect Method of Standardization:
Step 1: use a set of standard age-specific rates along with the
actual age composition of each population
Step 2: compute the number of events that would have occurred
in the two groups if each took on the age specific rates of the
standard population while retaining its own age distribution
Step 3: compute standardized event ratio as observed/expected
events for each group
The indirect method often concludes with this ratio.
Step 4: actual age adjusted rates for each group= event rate in
the standard population x standardized event ratio of the group
50. • Must know when to use an adjusted rate rather than crude rate
• If no confounders: the crude rate is adequate
• If confounders present: subgroup specific rates are sufficient
• Adjusted rates should be considered if they are meaningful
• If distribution of standard population is radically different than the
populations being compared, standardization is inappropriate
• Also, when direct standardization is applied, subgroup specific rates
should have same general trends in all the groups being compared as
well as in the standard population
•Direct method of standardization is used more frequently than
indirect method
• Direct method requires subgroup specific rates for all popns.
• Application of either method should lead to same conclusion
51.
52.
53.
54.
55.
56.
57.
58. Life Expectancy
• Summary of all age-specific mortality
rates
• Estimates hypothetical length of life of
a cohort born in a particular year
This assumes that current mortality rates
will continue
64. Sources of Morbidity Statistics
• Clinical and hospital
• Managed care
• Registries
• Vital statistics
• Surveys
• Disease reporting
• Insurance and pre-paid med. care
plans
• Absenteeism records
65. Terms Related to Morbidity
• Morbidity
The extent of illness, injury or disability in a
defined population
• Incidence of a disease (Incidence rate)
The number of new cases of a disease that
occur during a specified time period
(numerator) in a population at risk for
developing the disease (denominator)
• Prevalence of a disease (Prevalence rate)
The number of total cases of disease present
at a particular time (numerator) in a specific
population (denominator)
• Risk
The likelihood that an individual will contract a
disease
66. Characteristics
RISK PREVALENCE INCIDENCE
RATE
Probability of
disease
% of pop. with
the disease
Rapidity of
disease
occurrence
No units No units Cases per
person-time
Newly
diagnosed
Existing Newly
diagnosed
“Cumulative
incidence”
“Incidence
density”
67. 1. “Do you currently have asthma?”
Point prevalence
2. “Have you had asthma during the
last 1 years?” Period prevalence
3. “Have you ever had asthma?”
Cumulative incidence
67
68. Other Measures of morbidity
1. Notification rate
2. Attendance rates at OPD, health
centers
3. Admission, readmission, and
discharge rates
4. Duration of stay in the hospital
5. Spells of sickness or absence from
work or school
68
72. Incidence
The two forms of incidence are:
• Cumulative incidence
• "risk of disease“
• measures the proportion of
persons who develop a disease in a
known span of time
• Incidence rate
• "rate of disease“
• measures the rate of new disease
occurrence over time
73. Cumulative incidence
• Cumulative Incidence =
Number of people who get a disease
during a specified period * 1000
Number of people free of the
disease in the population at risk at
the beginning of a study period
73
74. Incidence Rate
• Measures the rapidity with which newly
diagnosed cases of the disease of interest
develop
observe a population
count # of new cases
measure net time
• individuals in population at risk of developing disease
• person-time
person-years
patient-days
75. Incidence rate per 1,000
• Number of new cases of a disease
occurring in the population during a
specified period of time * 1000
Number of persons who are at risk
of developing the disease during that
period of time
75
76. Incidence density
• if people at risk are observed for
different periods of time
• The denominator consists of the sum
of the units of time that each individual
was at risk and was observed.
• This is called person-time and is often
expressed in terms of person-months
or person-years of observation.
76
77. Person time
• 1 person at risk who is observed for
one year = 1 person-year.
• 1 person at risk observed for 5 years
= 5 person-years.
• 5 people at risk, each of whom is
observed for only 1 year = 5 person-
years.
77
78. Incidence Rate (Attack Rate) (cont.)
• Can be used for specific exposures
• Also used for multiple exposures
• Other terms:
primary case
secondary attack
• secondary cases
83. Prevalence
• Measure of the number (or proportion) of
cases in a given population
• What is the difference between prevalence
and incidence?
Prevalence → a slice thru a population at a
given point in time that determines who has
the disease and who does not, while Incidence
only looks at new cases
• In steady state situation (no change in rate
or net population)
Prevalence = Incidence X Duration of disease
90. Expectancies and Gaps
• From a typical survival
curve, we can either
consider the life
expectancy (“E”), or the
gap (“G”) between
current life expectancy
and some ideal.
• Expectancies are
generic; gaps can be
disease-specific (e.g.,
life yrs lost due to
cancer)
G
0%
20%
40%
60%
80%
100%
0 10 20 30 40 50 60 70 80 90 100
E
91. Classifying Health Gaps
• Gaps: Compare population health to
some target. = Difference between time
lived in health states less than ideal
health, and the specified target
• The implied norm or target can be
arbitrary, but must be explicit and the
same for all populations being compared.
The precise value does not matter
92. Gaps: Expected Years of Life
Lost
• Uses population life expectancy at the
individual’s age of death
Problems: different countries may have different
life expectancies. It’s overall mortality, so cannot
identify impact of a disease.
• Standard Expected Years of Life Lost
Reference is to an “ideal” life expectancy
• E.g., Japan (82 years for women)
• Area between survivorship curve and the chosen norm
93. Potential Years of Life Lost
(PYLL)
• PYLL = ( “normal age at death” – actual
age at death). Doesn’t much matter what
age is chosen as reference; typically 75
• Attempts to represent impact of a disease
on the population: death at a young age is
a greater loss than death of an elderly
person
• Focuses attention on conditions that kill
younger people (accidents; cancers)
• All-causes or cause-specific
94. 3. Aggregate Measures that
Combine Mortality &
Morbidity
Health expectancies
Health gaps
95. Composite Measures
• Aim to represent overall health of a population
• Composite measures combine morbidity and
mortality into a health index. (An index is a
numerical summary of several indicators of
health)
• Mortality data typically derived from life
tables; morbidity indicators from health
surveys, e.g.
• Self-rated health
• Disability or activity limitations
• A generic health index
96. Different Types of Morbidity Scales
for Use in Composite Measures
• Generic instruments cover a wide range of
health topics, e.g. reflecting the WHO
definition. These can be health profiles (e.g.,
Sickness Impact Profile, SF-36) or “health
indexes” (e.g., Health Utilities Index,
EuroQol)
• Specific instruments
Disease-specific (e.g., Arthritis Impact
Measurement Scale)
Age-specific (e.g., Child Behavior Checklist)
Gender-specific (e.g., Women’s Health
Questionnaire)
97. Survivorship Functions for Health
States
G
0%
20%
40%
60%
80%
100%
0 10 20 30 40 50 60 70 80 90 100
H
Survivors
Age
This diagram extends the earlier
one by recognizing that not all
survivors are perfectly healthy.
The lower area ‘H’ shows the
proportion of people in good health
(however defined); it shows healthy
life expectancy. The top curve
shows deaths; intermediate area
represents levels of disability.
Area ‘G’ again represents the
health gap. The question arises
whether the people with a disability
ought to be counted with H or with
G.
Deaths
98. Health expectancies
• Generic term: any expectation of life in
various states of health. Includes
other, more specific terms, such as
Disability Free Life Expectancy
• Two main classes:
Dichotomous rating: two health states
Health state valuations for a range of
levels
99. I. Dichotomous
expectancies
• Here full health is rated 1, and any state of
poor health (mild, moderate, severe
disability) is rated 0.
• This leads to Disability-free life expectancy
(DFLE): weight of 1 for “no disability” and 0
for all other states.
• = Expectation of life with no disability, or
Healthy Life Expectancy (HLE)
• Very sensitive to threshold of disability
chosen
Sullivan(1971)
100. II. Polytomous states and valuations
(Wilkins and Adams-1983)
• These incorporate many levels of disability into
life expectancy estimates and count time spent
with each level of disability.
• Polytomous model (three or more health states
defined: weights assigned to each; generally 0 to
1.0. These may be added together and compared
across diseases)
• = Health-adjusted life expectancy (HALE)
• First calculated for Canada by Wilkins. Four
levels of severity & arbitrary weights.
• Recent work uses utility weights. E.g. from
Health Utilities Index, Quality of Well-Being Scale,
EUROQoL, etc.
101. Polytomous Curves Showing
Quality of Survival
G
0%
20%
40%
60%
80%
100%
0 10 20 30 40 50 60 70 80 90 100
H
Survivors
Age(years)
This diagram illustrates
several classes of disability,
each having a separate
severity weighting.
The area ‘H’ again includes
healthy people, but the
definition may have changed.
The top curve shows deaths;
intermediate curves represent
various levels of disability.
Deaths
102. Relationship between Life Expectancy,
Health Expectancy and Health-Adjusted
Life Expectancy
Health-Adjusted
Life Expectancy
Life
Expectancy
Healthy
Life
Expectancy
By down-weighting the
various levels of
disability,the HALE falls
between LE and HLE
103. Gap Measures: QALYs &
DALYs
• Gap measures can also use a weighting for
intermediate health states. This is necessary
to combine time lost due to ill health with
time lost due to premature mortality
• Quality Adjusted Life Years (QALYs) lost
Common outcome measurement in clinical trials,
program evaluation
Record extra years of life provided by therapy and
quality of that life
Typically use utility scale running from 0 to 1
• DALYS (disability-adjusted life years) lost
104. Complementarity of Health
Expectancies and Health Gaps
SLE
LE
HALE
HLE
LE SEYLL
SURVIVAL
HALE HALY
POLYTOMOUS
HLE ?
DICHOTOMOUS
Birth
LE = Life Expectancy; SLE = Standard LE; HALE = Health-Adjusted LE;
HLE = Healthy LE; SEYLL = Standard Expected Years of Life Lost
HALY = Health-Adjusted Life Years Lost
Gaps
Expectancies
Age
106. What are DALYs?
• DALYs = Disability Adjusted Life
Years
• A common measurement unit for
morbidity and mortality
• Facilitates comparisons of all
types of health outcomes
107. Possible use of DALYs
• Quantitative analysis of the burden
of disease
• Analysis of cost-effectiveness of
alternative interventions
• Selection of a package or list of
interventions deliverable within the
available budget
JL Bobadilla, WHO: 1996
108. What is the Global Burden of
Disease study?
• Backed by the WHO and the World
Bank
• A quantitative overview of the burden
of disease world-wide
• Combines information about loss of
quality of life with traditional
epidemiological information on
mortality
• All health outcomes are expressed in
DALYs
109. 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
111. How are DALYs
constructed?
• A DALY is a health outcome
measure with two main
components
Quality of life reduced due to a
disability
Lifetime lost due to premature
mortality.
112. DALYs due to living with disability
(Red area measures DALYs. Red + white is a “normal”
life)
82,5 YEARS
NO
DISABILITY
113. DALYs due to early death
(Red area measures DALYs. Red + white is a standard
life)
NO
DISABILITY
82,5 YEARS
114. DALYs due to disability and premature
death combined.
NO
DISABILITY
82,5 YEARS
115. Calculation of DALYs
(age-weighting and discounting are
omitted for didactic reasons)
• 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) :
• Number of healthy life years × the disability
weight of full health (0) + life years with
disability (50) × disabilty weight for deafness
(0,33) + life years lost (30) × the weighting of
death (1)
• 5 × 0+ 45 × 0,33 + 30 × 1 = 47.35 DALYs
116. DALYs and QALYs
• DALY is a modification of QALY
(Quality Adjusted Life Years).
• Both concepts combine information
about length of life and quality of life.
• A DALY is a negative QALY.
117. Relation between QALYs and DALYs
DALYs = healthy years lost
QALYs = healthy years gained
NO
DISABILITY
82,5 YEARS
118. How are disability adjustments
made?
The methods used to assign a disability
weightings to life years is a critical part of
the DALY approach.
– 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.
119. Current method used for
weighting disability
• Disability weights are obtained by
posing two different Person Trade-
Off (PTO) questions to expert panels
• PTO1 compares life extensions for
disabled and healthy people
• PTO2 compares cures for illness
with extension of life
120. Other choices behind DALY
• In addition to adjusting the value of
life years with disability weights, and
chosing 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
• Age weighting
– life years of children and old people are
counted less
123. 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
= 10.5 DALYs
124. PROBLEMS of the DALY
approach
• Is it true?
Questions of the validity of the
results
• Is it just?
Questions of the distribution
between groups
125. 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
126. Validity problems of the
current PTO protocol
• Lack of simplicity, difficult to
understand
• Forced consistency between two
questions that are essentially
different
• Impossible to answer that all
individuals are equally valuable
• The expert panel may not represent
the values of other people
127. Validity problems of
epidemiological estimates
• Epidemiological data for Africa, Latin
America and Asia are crude estimates.
• The uncertainty of the figures of
prevalence, may be hidden in the
seemingly mathematical rigor of the
results.
• Lack of uniform diagnostic criteria. I.e.
what do we mean by “depression”?
128. Justice
• The DALY approach has been
criticised for discriminating
– the young
– the elderly
– future generations (future health
benefits)
– the disabled
– women
129. The young
• The 5-year-old girl in the example
above yielded 10,5 DALYs.
• However, the DALY score without
age-weight and discounting would
be
• 77.5 × 0.3 = 23,3 DALYs
• This result is twice as high, and
would give her a higher priority.
130. The elderly
• In the literature on justice in health
care, many agree that given a choice,
it is more important to save young
adults than the very old.
• This view is captured by the DALY
(as a time based measure) itself.
131. Future generations
• The practice of discounting future
benefits is also controversial.
• From society’s viewpoint, why should a
life year now be of more value than a
life year twenty years ahead?
• The implications for preventive
services versus curative services are
significant. Preventive interventions are
given less weight.
132. The disabled
• The DALY approach opens for including
chronic illnesses and disabilities in cost-
utility calculation. This is an improvement.
• On the other hand, the current person trade-
off protocol explicitly assumes that lives of
disabled people have less value and
• implies that disabled people are less entitled
to health resources to extend their lives
133. Example of results
• In the protocol behind the present Global Burden of
Disease, a life year for 1000 healthy people has been
set as equally valuable as one life year for
– 9524 people with quadriplegia
– 2660 blind people
– 1686 people withDown's syndrome without
cardiac malformation
– 1499 deaf people
– 1236 infertile people
• WHO has announced a change in approach.
134. Women
• Underlying value choice: Standard
expectation of life at birth is 82.5 years
for women, 80 years for men
• The ‘true’ gender gap is greater
• Gender gap is adjusted to correspond
to ‘biological differences in survival
potential’
• Critique: Might underestimate burden
of disease for females relative to males
135. Anand S, Hanson K. Disability-adjusted life years: a critical
review. Journal of Health Economics 1997;16:658-702.
Arnesen T, Nord E. The value of DALY life: problems with
ethics and validity of disability adjusted life years. BMJ
1999; 319:1423-1425.
Bobadilla J-L, Cowley P, Musgrove P, Saxenian. Design,
content and financing of an essential national package of
health services. Bulletin of the World Health Organization
1994;72:653-662.
REFERENCE LIST
136. Murray CJ, Lopez AD. Global mortality,
disability, and the contribution of risk factors:
Global Burden of Disease Study. Lancet
1997b;349(9063):1436-42.
Murray CJ, Lopez AD. Mortality by cause for
eight regions of the world: Global Burden of
Disease Study. Lancet 1997c;349(9061):1269-
76.
Murray CJ, Lopez AD. Regional patterns of
disability-free life expectancy and disability-
adjusted life expectancy: global Burden of
Disease Study. Lancet 1997d;349(9062):1347-
52.
Notes de l'éditeur
he U.S. census has been criticized for selective undercounting, particularly of minorities and illegal aliens living in the inner cities. Undercounting affects the level of federal contributions to welfare programs as well as the apportionment of congressional representation. In some Third World nations the problem of undercounting is more severe, especially in countries like India, with a large homeless population, or those with nomadic populations. An increasing U.S. homeless population resulted in 1990 in the first large-scale effort by the U.S. Census Bureau to count that group. Census workers visited several thousand shelters and open-air sites in cities mainly of 50,000 or more population
Gives less weight to diseases of old age than than diseases of childhood. Results depend on age defined as normal.. Used to be 65, is not 85.
The authors have contributed equally much to the presentation. In alphabetical order: Trude M. Arnesen, MD, MPH. PhD student, National Institute of Public Health, Pb 4404 Nydalen, 0403 Oslo, Norway. E-mail: trude.arnesen@folkehelsa.no Ole Frithjof Norheim, MD, Ph.D. Associate professo, Department of Public Health and Primary Care, University of Bergen, Norway. E-mail: ole.norheim@isf.uib.no
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.
DALYs can be used in three interrelated areas: i) for epidemiological surveillance of the total disease burden (number of DALYs) ii) to measure cost- effectiveness of interventions (cost per avoided DALY) iii) to decide what should be included in a country’s ‘core services’ (the package of essential health care services). Within a fixed budget, it has been suggested that only the most cost-effective interventions should be included (cost per avoided DALY) . The concept of DALYs thus provide challenging information for policy makers concerned with international health, the health of developing countries, and national priority setting.
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 ).
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 1997. (Murray, 1997) The following table shows the leading causes of world-wide lost DALYs for both sexes in 1990 and the projections for 2020.
The figure shows the projections made for the year 2020. ( Murray and Lopez, 1997 a) We note that the importance of the disorders typical for children and the poor seem to decline, and the disorders typical for older age groups incline. One reason is the expected demographic transition (life expectancy increases in many countries) that is followed by an epidemiological transition (the disease burden in total changes with increasing number of people in the various age groups).
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.
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.
Premature death from a myocardial infarction, say at age 50, would produce the DALY-loss as depicted by the read area in the figure. This patient’s loss is 33.5 years. No adjustment is made for disability because the patient dies.
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:
This example is, for didactic reasons, a simplified way of calculating DALY loss, omitting age-weighitng and discounting.
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 complementarity between the two concepts can be illustrated schematically:
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).
If, for instance, we want to find the burden of bach ache, we must first define what we mean by bach 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 disabilty 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.
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 ]
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 ). Discountingmeans that future gains and losses are counted less than if they had occured 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.
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, 1993 . 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.
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! Similarly, if a person dies when he is 24 or if he dies when he is new born, yields the same number of DALYs.
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 a 1 , multiplied with a discounting factor d 2 (3 % for each year). The estimated DALY loss would be 77.5 (82.5 - 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.
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.
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.
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.
Cooper et al have argued that the data used for e.g Sub-Saharan Africa are of so poor quality that the estimates made for this regions are seriously in doubt (Cooper, 1998 ). Lack of uniform diagnostic criteria, example: -do different countries agree on whom to call and count as “depressed”? -do different panel members mean the same when evaluating the burden of being “depressed”?
The approach has been criticized for violating the principle of treating people as equals. In the following these concerns are examined.
The burden of disease (and effect of interventions) for young people, is given less importance by the combined effect of age weighing and discounting. The principle of equal worth of people would require the same age weight for all. It remains an open questions whether the reasons given for departing from equal age weights for all are acceptable. Considering the consequences (children might be given less priority when calculating burden or effect of interventions), it could be seen as an unreasonable (and unnecessary) value judgment.
Age weights implies, for example, that living with a disability, e.g. blindness, for a person aged 80 is considered less bad than living with blindness for a 25 year old person. It is unclear why the DALY measure needs to discriminate between the value of a life years at different ages. (Harris1985, Williams 1997)
On the issue of discounting researchers disagree, and there are good reasons for adopting both views. For a defense of discounting, see ( Murray, 1996) . For a rejection of discounting, see ( Anand, 1997).
The DALY approach which is the basis of the Global Burden of Disease currently in use has been much critisized because the method presupposes that life years of disabled people are worth less than life years of people without disabilities. The method assumes that disabled people are less entitled to scarce health resources for interventions that would extend their lives. The line of thought from the first question to the application in cost effectiveness analyses seems to be that the healthier the person, the more valuable their life is to themself and to society and the greater their claim on restricted healthcare resources to have their life extended. This makes sense only if the value of life is not seen as a dimension distinct from health, but rather as a direct positive function of health. At worst, this line of thinking could lead to the following table:
The PTO1 questions regards which number of disabled people is required for a life extension of 1 year for this group to be equally valuable as for a group of healthy people. The higher the number of disabled people “on the balance”, the higher the disability weight of this diagnostic group. From the current, published, disability weights, we can calculate the mean answer of the panel participants to this question as shown above. A valuation of human beings according to their functional capacity is in contrast to the humanistic values laid down in the Declaration of Human Rights: "recognition of the inherent dignity and of the equal and inalienable rights of all members of the human family is the foundation."19 The WHO department responsible for the global burden of disease project aims at "strengthening the scientific and ethical foundations of health policies.... The aim of the work is to promote equity, quality, and efficiency.”(ref) The current DALY protocol does not seem to accord with this. (Arnesen and Nord, 1999)
Gender gap is adjusted to correspond to ‘biological differences in survival potential’ according to (Murray, 1994) Critique: If maximum standard expectation of life at birth is, say 78 years for men, but is adjusted to 80 years in the Burden of Disease study, the estimated burden for men thus becomes greater relative to women. DALYs lost underestimate burden of disease for females relative to males(Anand, 1997, Sundby 1999).