burden of disease using dalys
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Abdur Razzaque Sarker, MHE (Health Economics) , MSS (Economics)Health Economic and Financing Research GroupICDDR,BEmail: [email protected]
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Concept of DALYsBackground Difference between QALYs and DALYs Health gaps Components of DALYs Principles of DALYs Practice Estimated DALYs in Worldwide Estimated DALYs in Bangladesh
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The global burden of disease study report was released in 1996
The disability-adjusted life year (DALY) is a measure of overall diseases burden expressed as the number of years lost due to ill-health, disability or early death.
The burden of disease methodology was developed by researchers at
Harvard University and the World Health Organization for the World Bank to quantify the amount of premature mortality and disability present in any given population.
The summary measure that the methodology derived was the Disability Adjusted Life Year or DALY
Background
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Differences between QALYs and DALYs
DALY and QALY are both used as measuring health
QALYs DALYsQALY= Quality Adjusted Life Years DALY= Disability Adjusted Life Years
QALY measures the quality of life in health gain
DALY measures health loss in the quality of life
QALY is expressed in either 1 or 0, Where1 = Perfect Health 0= Death
DALY is expressed in either 0 or 1, WhereO = Perfect Health 1= Death
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Disability Adjusted Life Years (DALYs)
DALY is the only quantitative indicator of burden of diseases that reflects the total year lost (pre-mature mortality) or some degree of disability (morbidity) during a period of time.
Premature mortality is measured as years of life lost (YLLs)Morbidity is measured in terms of years lived with a disability (YLDs)
Thus , DALY = YLL + YLD
One DALY represents one lost year of healthy life
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For example, the DALYs for road traffic accidents in any given area is defined as the total YLLs in fatal road accidents added to the total years of life lived with disabilities by survivors of accidents in the same year.
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Health Gaps: Social value choices
1. How long should people in good health expect to live?
2. Is a year of healthy life gained now worth to society than a year of healthy life gained sometime in the future?
3. How should we compare years of life lost through death with years lived with poor health or disability of various levels of severity?
4. Are lost years of healthy life valued more at some ages than others?
5. Are all people equal?
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Health Gaps: Social value choices1. How long people in good health expect to live?
Standard life expectancy
2. Value of future years of Discounting
3. Compare years lost due to death with years lived in poor
health Disability weight
4. Value of healthy years of life at all ages.
Age weight
5. Same values for all regions of the world
All people are equal
These are the five components of DALYs
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1. Standard life expectancy
The DALY measures health gaps as opposed to health expectancies
It measures the difference between a current situation and an ideal situation where everyone lives up to the age of the standard life expectancy, and in perfect health.
Based on life tables, the standard life expectancy at birth is set at 80 years for men and 82.5 for woman according to Japan because of highest life expectancy
It is better to use country specific life expectancy from a life table
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2. Discounting
People generally prefer a healthy year of life immediately, rather than in the future, if given the choice
The GBD study applied a 3% time discount rate to years of life lost in the future
The value of health gains today compared to the value attached to health gains in the future
Discounting function = e – r (x-a)
Wheree = Constant equal to 2.71r = Discount rate; 3%, 5% x = agea = age at onset
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3. Disability weight
In the calculation of the DALY, a weighting system is used to measure the severity of a disability
The disability weight is measured on a scale of zero to one
0 1Full health Death
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Disability classes in GBD 1990
Disability
class
Severity
weights
Indicator conditions
1 0.00 – 0.02 Vitiligo on face, weight-for –height less than 2SDs
2 0.02 – 0.12 Watery diarrhoea, severe sore throat, sever anemia
3 0.12 – 0.24 Radius fracture in stiff cast, infertility, angina,
arthritis
4 0.24 – 0.36 Deafness, below the knee amputation
5 0.36 – 0.50 Mild mental retardation, Down syndrome, Fistula
6 0.50 – 0.70 Unipolar major depression, blindness, paraplegia
7 0.70 – 1.00 Active psychosis, dementia, severe migraine
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Disease or sequelae Mean disability weight
(untreated form)
Mean disability
weight (treated form)
AIDS 0.50 0.50
Diarrhea disease, episode 0.11 0.11
Tuberculosis 0.27 0.27
Trachoma, blindness 0.60 0.49
Unipolar major depression 0.60 0.30
Cancer 0.81 0.81
Asthma, cases 0.10 0.06
Malaria, episodes 0.20 0.20
Some Diseases Specific Weight
Source: Murray & Lopez (1996)
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4. Age weight
There is a broad social preferences to value a year lived by a young adult more highly than a year lived by young child or at older ages
Not related to productivity but social role in caring for the young and old.
Age Weighting Function = C x e – β x
Where,
C = Constant equal to 0.1658β = Constant equal to 0.04
e = Constant equal to 2.71
x = Age
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5. Health is simply added across individuals
Two people each losing 10 years of disability-free life are treated as the same loss as one person losing 20 years
One could also weight duration non-linearly, so as to give priority to fewer people suffering for long intervals over more people suffering for shorter intervals
It is lead -all people are equal
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Principle of DALYs
The DALY combines in one measure the time lived with disability and the time lost due to premature mortality:
DALY = YLL + YLD
Where,YLL= Years of Life LostYLD= Years Lived with Disability
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Calculating YLL and YLD
The basic formula for calculating the YLLYLL = N x L
where:N = number of deaths.L = standard life expectancy at age of death (in years)
The basic formula for calculating the YLDYLD = I x DW x L
where:I = number of incident cases.DW = disability weight.L = average duration of disability (years)
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Applying with a 3% discount rate
YLL becomes:
Where, N = number of deaths.L = standard life expectancy at age of death (years)r = discount rate
YLL = N * (1 – e-0.03L)
0.03
YLD becomes:
Where, I = number of incident casesDW= disability weight L = duration of disability (years)r = discount rate
YLD = I * DW * (1 – e-0.03L)
0.03
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Applying with discounting and age-weight
The initially simple formulas for YLL and YLD become more complicated YLL becomes:
YLL= N KCe(ra) / (b+r)2 [e-(b+ r) (L+a) [-(b+r) (L+a)-1] - e-(b+ r)a [–(b+r)a-1]]
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YLD = I * DW * K Ce(ra) / (b+r)2 [e-(b+r)(L+a) [-(b+ r)(L+a)-1] - e-(b+ r)a [–(b+r)a-1]]
Where,
I = number of incident casesL = duration of disabilityD = disability weightx = agea = age at onset/ age of deathr = discount rate C = constant
β = constant
K = constant
YLD with discounting and age weight
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Practice
Q. A woman become sick with a bipolar depression at age 35, that she has it for 10 years and dies as a result.
How many DALYs(0.03,1,o.o4) have been lost as a resultSuppose, life expectancy is 79.13 years.
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Case 1: DAL Ys Lost Due to Immediate Death
The horizon for this case is(10 years disable) (34.73 Years lost)
35 YLD 45 (YLL) 79.13
In this case, L = Years lived with disability = 10D = disability weight =0.6a = age at onset/ age of death= 35r = discount rate = 0.03C = constant =0.1658
β = constant = 0.04
K = constant = 1e = constant = 2.72
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YLD = I * DW * K Ce(ra) / (b+r)2 [e-(b+r)(L+a) [-(b+ r)(L+a)-1] - e-(b+ r)a [–(b+r)a-1]]
Case 1 : To calculate YLD
=0.6{1*0.1658*2.72(0.03*35)/(0.03+0.04)2[2.72-
(0.03+0.04)(10+35)[-(0.03+0.04)(10+35)-1]-2.72-(0.03+0.04)35[-
(0.03+0.04)35-1]]
=6.95
The number of DALY loss due to disability is 6.95
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Case 2 : To calculate YLL
It requires two steps
1. The years of life lost from age 45 onwards is calculated
2. This value is converted to the expectation of life lost from age 35 so all DALYs can be added up from age 35 onwards using common metric.
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The first steps requires a straightforward substitution of values into general YLL equation using the following values
In this case,
L = Life expectancy at age 45 = 34.73a = age at onset/ age of death= 45r = discount rate = 0.03C = constant =0.1658
β = constant = 0.04
K = constant = 1e = constant = 2.72
YLL= N K Ce(ra) / (b+r)2 [e-(b+ r) (L+a) [-(b+r) (L+a)-1] - e-(b+ r)a [–(b+r)a-1]]
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YLLs [0.0,1,0.04] =
1*0.1658*2.72(0.03*35)
/(0.03+0.04)2[2.72
-(0.03+0.04)(34.73+45)
[-(0.03+0.04)(34.7+45)-1]-2.72-(0.03+0.04)45
[-(0.03+0.04)45-1]]
=19.97
The total DALYs lost from the age of 45 onwards, due to lost years of life is therefore 19.97
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Second Step
The second step is to convert DALYs at age 45 (19.97) to age
at onset , 35 years with following formula
DALYs at age 35 = DALYs at age (45)× e-rs
where s is the number of years to be discounted, that is (45-35)
= 10
DALYs at age 35 = 19.97× 2.71-(0.03×10)
= 14.80
Hence, Total DALYs Lost = YLD + YLL
= 6.95+14.80
= 21.75
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Calculating DALY: Sensitivity Analysis
Discounting at 0%, 3%, 5%
Age weighting – yes / no
DWs – Dutch weight, GBD weights
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We can Calculate DALYs using MS Excel
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If we consider 60-69 ages the estimated DALYs will be
DALYs = YLL (Male + Female) + YLD (Male + Female)
=(174919+196437)+(77755+116632)
=(371365+194387)
=565743
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Using DISMOD software we can estimate the burden of diseases.It is a free software available in www.who website The original version of DISMOD is available from the Burden of Disease Unit, Harvard University. For downloading the software visit,
www.hsph.harvard.edu/organizations/bdu/dismod
DISMOD
www.icddrb.orgMurray CJ, Lopez AD. N Engl J Med 2013;369:448-457.
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Findings: Global Burden of Disease in DALY, 1999 (000s)
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Findings: DALY (000s), Bangladesh, 1990Disease Category Male Female
DALY % DALY %
Respiratory 3766.4 17.2 4100.1 16.6
Perinatal causes 3240.4 14.8 3354.0 13.6
Injury 3066.0 14.0 2387.5 9.7
Diarrhoeal 2741.7 12.5 3006.7 12.2
Maternal - 0.0 2889.9 11.7
Nutrition 2156.7 9.9 2595.5 10.5
Cardiovascular 1592.5 7.3 1455.6 5.9
Neuro-Psych & Sense 1407.5 6.4 1605.5 6.5
Childhood INF 1189.5 5.4 1193.1 4.8
Congenital 541.2 2.5 550.9 2.2
Tuberculosis 796.0 3.6 456.5 1.8
Digestive 516.6 2.4 306.9 1.2
Malignant Neoplasm 433.0 2.0 497.5 2.0
Tropical Disease 281.6 1.3 127.4 0.5
Diabetes 143.4 0.7 150.0 0.6
Total 21872.5 100.0 24677.1 100.0
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Thank You All