Post on 16-Jan-2016
Damage Function Damage Function ModelsModels
Dave StiebDave Stieb
“And it was so typically brilliant of youto have invited an epidemiologist”
3
Quantifying Health Benefits
Cleaner fuel
Reduced vehicle emissions
Sulphates SO2 NOX VOCsCO
Improved ambientair quality
Reduced population exposure
$/QALYValue to society
Air Pollution
20 30 40 50 60 70 80 90
Hea
lth
Ou
tco
me
108
110
112
114
116
118
120
Air Pollution
20 30 40 50 60 70 80 90
Hea
lth
Ou
tco
me
108
110
112
114
116
118
120
Improved public health
Representing the weight of Representing the weight of
evidenceevidence How do you choose a parameter How do you choose a parameter
value?value?• Expert judgment– Flexible, streamlined– Can be seen as arbitrary
• Systematic overview and meta-analysis– Rigorous, comprehensive– Rigid, cumbersome
• Structured “consensus” process (eg. Delphi), expert elicitation– Middle ground
Dealing with uncertaintyDealing with uncertainty
• WHAT IF the parameter were different?• Sensitivity analysis
– Run the analysis a few times and see how the results change
• Probabilistic analysis– Run the analysis thousands of times (iterations)– For each iteration, pick a different value for each
parameter, from an input distribution– The results are also presented as a distribution: “most
likely value of benefits is y, but could be as low as x and as high as z”
• 1996 –• Numerous policy
applications:– Acidifying emissions
– AQOs
– Sulphur in gas
– CWS
– Climate change co-benefits
• Peer reviewed
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Sulphur in Gasoline
• Canadian gasoline sulphur levels ranged from <10 to 1000 ppm with national average of 340 ppm
• In 1999, federal regulation took effect to reduce average sulphur content of gasoline to 30 ppm by 2005
Reductions - large for SO2, sizable for NOx and SO4, still interesting for others
Toronto Vancouver Saint John Avg 7 CitiesGases
SO2 25 / 34 14 / 20 3 / 4 9 / 12
NOx 6 / 7 6 / 5 4 / 4 4 / 4 VOC 3 / 4 1 < 1 1 O3 1 1 - 1 CO 6 / 8 2 / 3 3 / 3 Particles
SO4 7 / 9 4 / 5 1 / 2 3 / 4
PM2.5 1 / 2 < 1 < 1 1
% Reductions vs Current Ambient Air LevelsYear 2001 / 2020 - Gasoline at 30 ppm
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Findings of Health Panel for seven cities only, in 2001- Reducing sulphur to 30 ppm improves the health of Canadians
ESTIMATED* CASES
AVOIDED
53
60
168
82,300
39,000
281,400
2,300
187
prematuremortality
emergency room visits
restricted activity days
acute respiratory symptoms
asthma symptom days
hospitaladmissions
bronchitis in children
chronic bronchitis
incr
ease
d se
veri
ty o
f ef
fect
March 23, 1998
“The doctor will bill you now”
0
50
100
150
200
250
300
350
400
450
500
Gas oline 4 Gas oline 6 Dies el 1 Dies el 3
1994
$ (
mill
ion
s)
Total
Mortality
Chronic Respiratory Disease
Other
Benefits for Year 2001 by type for 4 alternative scenarios; central, low and high estimates
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Health Benefits vs. Refinery CostsHealth Benefits vs. Refinery Costs
7.4
0.6
1.9 1.6
0.0
2.0
4.0
6.0
8.0
10.0
S Ont &SW Que &
SW BC
Rest
Net
Pre
sen
t V
alu
e ($
Bil
lio
ns)
(200
1-20
20)
Benefits
Costs
Benefits and costs based on 30 ppm (total population)
( 45% of Canadian
Population )
To do listTo do list Alternative methods of mapping monitoring data to populations (eg. geostatistical methods) Update baseline air quality data Alternative status quo air quality (don’t just assume constant) Alternative population projections (allow different assumptions about birth rate, mortality rate,
immigration and internal migration) Update to 2001 census Update risk coefficients Derive risk coefficients more systematically Allow risk coefficients to differ by geographic area Allow baseline morbidity, mortality rates to differ by geographic area Allow non-linearity in concentration response Permit multi-year analysis More flexible approach to uncertainty analysis (not just discrete three point distributions) Alternatives to $ valuation (eg. QALYs)
ICAP• Ontario version released
in 2000• Expanded nationally• Peer reviewed• Currently being updated
• Includes database of concentration response functions, valuations
• Peer reviewed• Available
online
Key pointsKey points
• Reduced (increased) air pollution results in health and environmental benefits (damages)
• Alternative approaches to representing weight of evidence, uncertainty
• Improved health (and environmental quality) have value to society
• Variety of tools available to assess benefits
Extra slidesExtra slides
• Damages– Burden on society from negative effects of air
pollution
• Benefits– Gain to society from reducing negative effects of
air pollution
How do we quantify the impact How do we quantify the impact of reduced (increased) of reduced (increased) exposure?exposure?
Air Pollution
20 30 40 50 60 70 80 90
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108
110
112
114
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Monetary ValuationMonetary Valuation
• AKA– monetization
• assigning a monetary value to a change in health status
• most appropriately measured as willingness to pay to improve health or willingness to accept compensation to worsen it
Image Problem - IImage Problem - I
• Unseemly • Valuation implicit in innumerable private and public decisions
• Either do it implicitly or explicitly, but can’t avoid it
• Balances singular focus on industry compliance costs
Image Problem - IIImage Problem - II
• Simply asking people their preferences is too hypothetical
• Considerable effort in developing valid and reliable measures
• Reality checks
Image Problem - IIIImage Problem - III
• Lives worth more in rich countries
• Distributional/ equity issues can be taken into account
Quality/ Disability Adjusted Life Quality/ Disability Adjusted Life YearsYears
Quality Adjusted Life Years(QALYs)
Quality of Life(0-1 scale)
Time(years)
= x
1 QALY = 1 year xPerfect health
(score of 1)
0.8 QALY = 1 year x score of 0.8
0.8 QALY = 0.8 year x Perfect healthOR
ShortcomingsShortcomings• People like QALYs/DALYs because simple, intuitive
– Huge following in clinical/ public health domain• BUT…• Some economists hate QALYs/ DALYs
– Don’t measure what they purport to measure (people’s preferences among health states)
• Ethical concerns– Discriminates against elderly, disabled
• Big question left unanswered:Q - how much should we spend to gain 1 QALYA - $40,000 (?) see also Harvard Cost-utility Analysis Database
1991 1992 1993 1994 1995 1996 1997 1998
Sulfate and Quality Adjusted Sulfate and Quality Adjusted Life ExpectancyLife Expectancy• Risk functions by age, sex, education, from re-
analysis of ACS cohort• Applied to population of Canada over lifespan• Change in life expectancy estimated• Quality adjustment based on health utilities index
from NPHS
ResultsResultsStudy Life Years Lost QALYs Lost
Brunekreef 0.19 (6 cities & ACS)
Nevalainen and Pekkanen
0.17 (6 cities)
0.09 (ACS)
Wolfsson
(smoking)
0.5 (females)
0.9 (males)
Coyle 0.05 (ACS) 0.01 (females)
0.07 (males)
• Risk coefficients from American Cancer Society cohort study applied to Canadian life tables
• Quality of life ratings from National Population Health Survey (Health Utilities Index)
• Substantial impact of sulfate on quality adjusted life expectancy
• Investment of over $1 billion/yr. would be warranted if it reduced sulfate concentrations by 1 µ g/m3.