Damage Function Damage Function ModelsModels

Dave StiebDave Stieb

“And it was so typically brilliant of youto have invited an epidemiologist”

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Quantifying Health Benefits

Cleaner fuel

Reduced vehicle emissions

Sulphates SO2 NOX VOCsCO

Improved ambientair quality

Reduced population exposure

$/QALYValue to society

Air Pollution

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Air Pollution

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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

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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.