risk analysis fundamental problems short course at harvard school of public health march 12th 2013...
TRANSCRIPT
Risk AnalysisFundamental problems
Short course at Harvard School of Public Health
March 12th 2013Richard Wilson
Mallinckrodt Professor of Physics (emeritus)Harvard University
Estimating A Risk should beNeutral (VERY HARD)
The distinction between calculation and blame or action should be
maintained
We always want to find a cause.. Usually to blame some one.
(often to collect money!) “Come, and let us cast lots,
that we may know for whose cause this evil is upon us”
“and the lot fell on Jonah”Jonah 1:7
1000 years ago various jurisdictions
tortured a suspect.
If he died under torture: too badIf he confessed he was guilty.
As late as 1950 UK common law considered Acts of God
differently from acts of manA brick falling from the roof was an
Act of Godwith no one to blame
UNLESSYou had put up a warning sign:
beware of falling bricks. Then you knew it was dangerous
In general the Courts are to decide conflicts between two parties not to
set societal standardsBUT
I and some others object when incorrect scientific statements are
made in court
Error (often disguised)It is an interesting hypothesis that:
Every cancer starts with a single hit on DNA (by radiation, fiber,etrc)
This is not directly provableBUT it is plabaly wrong to say the a
single radiati
Perennial conflict
Rights of an individual vs Rights of Society
Face the conflict do not ignoreQuarantinevaccination
Profiling (racial or otherwise)
Individuals usually and countries often want revenge
But revenge is rarely justice
Always forgive But NEVER forget
Since about 1970 analysts do not make the distinction
Natural Hazards can be analyzed and precursers found
Prevention of adverse consequences is similar for
natural and man made hazards
The Biggest Risk to Life is Birth. Birth always leads to death!
We talk about premature death.
Polls say Risk is Increasing (next slide)
but history says the opposite.
What do the polls mean?
More risk 38 60 55 43 78Less risk 36 13 26 13 6Same amount 24 26 19 40 14Not sure 1 1 0 4 2
Table 1-1. Public Opinion Survey Comparing Risk Today to Risk of Twenty Years Ago
Q: Thinking about the actual amount of risk facing our society, would you say that people are subject to more risk today than they were twenty years ago, less risk today, or about the same amount of risk today as twenty years ago?
Top Coroprate
Executives (N=401)
Investors, Lenders (N=104)
Congress (N=47)
Federal Regulators
(N=47)
Public (N=1,488)
Figure 1-1. Death Rates from 1900 to 1998 for Various Age Groups: United States
10
100
1,000
10,000
100,000
20001990198019701960195019401930192019101900
Date
Dea
ths
per
10
0,0
00
per
Yea
r
> 85
75 - 84
65 - 74
55 - 64
< 1
45 - 54
35 - 44
25 - 34
15 - 24
1 - 4
5 - 14
Note the little peak about 1918. What is it due to?
First world war? NO!Flu epidemic!
On the next slide we see the double dip in life expectancy for France.
For France flu was as bad as the war!
Figure 1-3aLife Expectancy
0
10
20
30
40
50
60
70
80
90
100
1750 1800 1850 1900 1950 2000
France
Japan
Sweden
Russia
Papua (54)
Gambia (37)
Palasra (52)
WHAT IS LIFE EXPECTANCY?
An artificial construct assuming that the probability of dying as
one ages is the same as the fraction of people dying at the same age at the date of one’s
birth.
The specific death rate Peaks, and the life expectancy at birth
has a dip at 1919world wide influenza epidemic.
BUT anyone born in 1919 will not actually see this dip.
Peculiarity of definition of life expectancy
Half the “Beijing men’ were teenagers.
This puts life expectancy about 15Roman writings imply a life
expectancy of 25.Sweden started life expectancy
statistics early.Russia has been going down
since 1980
Risk is Calculated in Different Ways and that influences perception and decisions.
(1) Historical data(2) Historical data where
Causality is difficult(3) Analogy with Animals
(4) Event tree if no Data exist
Risk is different for different measures of risk.
Different decision makers will use different measures depending
on their constituency
RISK MEASURES (continued)Loss of Life Expectancy (LOLE)
Years of Life Lost (YOLL)Man Days Lost (MDL)
Working Days Lost (WDL)Public Days Lost (PDL)
Quality Adjusted Life Years (QALY)Disability Adjusted Life Years (DALY)
Different decisions may demand different measures
LOLE from cigarette smoking
In USA 600 billion cigarettes made (presumably smoked)400,000 people have premature death
(lung cancer, other cancers, heart)1,500,000 cigarettes per death
Each death takes about 17 years (8,935,200 minutes) off life or
6 minutes per cigarette
ABOUT THE TIME IT TAKES TO SMOKE ONE(easy to remember)
Risks calculated from History seems simple. BUT
The number of people dying and
the number of persons in the risk pool often come from
different data bases.
Also units are often different
Forecasting the future based upn the pastWeather forecasting vs Fortune telling
1835 UK vagrancy act: fortune telling illegalIslam had a similar restriction
Scientists claim they are differentBUT
2008 Climate gate runs into the same problem.
Risks of New TechnologiesOld fashioned approach. Try it.
If it gives trouble, fix it. E.g. 1833
The first passenger railroad (Liverpool to Manchester) killed (a member of parliament) on the
first day!
Risks of New technologiesWe now want more safety
New technologies can kill more people at once.
We do not want to have ANY history of accidents.
Plot an EVENT TREEStart with an accident initiatorConsider a way of mitigation
effectsWhat happens when that does
not work?First done for nulear power:Rasmussens's reactor safety
study 1975
We try to get each step independent of the others. (Design a reactor that way)
Then the probabilities MULTIPLY
Accident frequency =P1 X P2 X P3 X P4
FloodEarthquake
Sabotage (terrorism) can couple to steps
TTHIS HELPS US TO FOCUS
The event tree analysis SHOULD have been used by NASA in the
1980s and it would have avoided the Challenger disaster
LNG facilitiesChemical refinery accidents
NASA adopt these proceduresHOPEFULLY SOON
Building IndustryOil well drilling
Three Different Metrics of Occupational Risk in Coal Mining, United States
0.00
1.00
2.00
3.00
4.00
1931 1941 1951 1961 1971 1981 1991
Year
Acc
iden
tal D
eath
R
ate
Per Million Man Hours
Per Million Tons ofCoal Mined
Per ThousandEmployees
Figure 1-5 Accidental Death Rates by Type of Coal Mine, U.S.
0.00
0.50
1.00
1.50
2.00
1931 1941 1951 1961 1971 1981 1991
Year
Acc
iden
tal D
eath
s pe
r m
illi
on m
an
hour
s w
orke
d Underground Mines
Surface Mines
Accidental Death Rates by Type of Coal Mine, U.S.
0
1
2
3
4
1931 1941 1951 1961 1971 1981 1991
Year
Acc
iden
tal
Dea
ths
per
mil
lion
ton
s of
coa
l pr
odu
ced
Underground Mines
Surface Mines
Three Different Metrics of Occupational Risk in Coal Mining, United States
0.00
1.00
2.00
3.00
4.00
1931 1941 1951 1961 1971 1981 1991
Year
Acc
iden
tal D
eath
R
ate
Per Million ManHours
Per Million Tons ofCoal Mined
Per ThousandEmployees
Accidental Death Rates by Type of Coal Mine, U.S.
0.00
0.50
1.00
1.50
2.00
1931 1941 1951 1961 1971 1981 1991
Year
Acc
iden
tal D
eath
s pe
r m
illi
on m
an h
ours
w
ork
ed Underground Mines
Surface Mines
Accidental Death Rates by Type of Coal Mine, U.S.
0
1
2
3
4
1931 1941 1951 1961 1971 1981 1991
Year
Acc
iden
tal D
eath
s pe
r m
illi
on to
ns o
f coa
l pr
oduc
ed Underground Mines
Surface Mines
Death Rates for Motor Vehicle Accidents in the United States
0
5
10
15
20
25
30
35
1925 1935 1945 1955 1965 1975 1985 1995
Year
An
nu
al D
eath
Rat
e
per 100,000 population
per 10,000 vehicles
per 1 million vehiclemiles
Annual Occupation Fatality Rates (US)
0
5
10
15
20
25
30
35
40
45
50
1978
1980
1982
1984
1986
1988
1990
(Year)
Death
s p
er
100,0
00
em
plo
yed
Agriculture, Forestry,Fishing
Mining
Construction
Manufacturing
Private Industry
Transportation andPublic Utilities
Wholesale & RetailTrade
Finance, Insurance,Real Estate
Services
EpidemiologyAssociate Death (or other Measure)
to Postulated CauseIs it statistically significant?
Are there alternative causes (confounders)?
THINK.No case where cause is accepted unless there is a
group where death rate has doubled.
Risk Ratio (RR) > 2
Correlation ofNumber ofBrooding sSorkswith NewbornBabies
Sies, H. (1988) Nature 332, 495
A contribution to epidemiology....
Associations vs. Cause-Effect
We contrast two types of medical response to pollutants.
ACUTE TOXIC EFECTA dose within a day causes death within a few days
(causality easy to establish)
CHRONIC EFFECTlower doses repeated give chronic effects
(cancer, heart) within a lifetime.(Causality hard to establish)
ANALOGY of animals and humans
Rodents do not look like people
Start with Acute toxic effectsdata from paper of Rhomberg and Wolf
(next slide)
Two problems in human diseases
Effect is often delayed from the Cause
then Causality is hard to prove.
Proof of an effect is at high dosewe want to know effect at low dose
Early Optimism Based on Poisons
There is a threshold below which nothing happens
__________
J.G. Crowther 1924
Probability of Ionizing a Cell
is Linear with Dose
Figure 2-7Alternative Dose-Response Models That Fit the Data
Dose
Re
sp
on
se Super Linear
Linear
Hockey Stick
Hormesis
Datum
Datum
Threshold
CRITICAL ISSUES FOR LINEARITY at low doses• THE POLLUTANT ACTS IN THE SAME WAY AS
WHATEVER ELSE INFLUCENCES THE CHRONIC OUTCOME (CANCER) RATE
• CHRONIC OUTCOMES (CANCERS) CAUSED BY POLLUTANTS ARE INDISTINGUISHABLE FROM OTHER OUTCOMES
• implicit in Armitage and Doll (1954)
• explicit in Crump et al. (1976)
• extended to any outcome Crawford and Wilson (1996)
Annual Death Rate By Daily Alcohol Consumption
0200400600800
1000120014001600
0 0.5 1 2 3 4 5 6
Average Number of Drinks Per Day
Dea
th R
ate
(Per
100
,000
)
Alcohol-augmentedconditionsCardiovasculardiseaseAll causes
Characteristics• One dose or dose
accumulated in a short time KILLS
• 1/10 the dose repeated 10 times DOES NOT KILL
Typically an accumulated
Chronic Dose equal to the Acute LD50
gives CANCER to 10% of the population.
Assumed to be proportional to dose
E.g. LD50 for radiation is about 350 Rems.
At an accumulated exposure of 350 Rems about 10% of exposed get cancer.
What does that say for Chernobyl?
(more or less depending on rate of exposure)
50% of all chemicals tested are carcinogenic in rodents
Scientific issue is the dose and the risk
Which are regulated is a political issue
.
Holiday Dinner Menushowing the natural carcinogens that are present
Appetizers
CREAM OF MUSHROOM SOUPhydrazinesCARROTS
aniline, caffeic acidCHERRY TOMATOES
benzaldehyde, caffeic acid, hydrogen peroxide, quercetin glycosidesCELERY
caffeic acid, furan derivatives, psoralensAssorted Nuts
MIXED ROASTED NUTSaflatoxin, furfural
Green SaladTOSSED LETTUCE AND ARUGULA WITH BASIL-MUSTARD VINAIGRETTE
allyl isothiocyanate, caffeic acid, estragole, methyl eugenolEntrees
ROAST TURKEYheterocyclic amines
BREAD STUFFING (WITH ONIONS, CELERY, BLACK PEPPER & MUSHROOMS)acetaldehyde, ethyl alcohol, benzo(a)pyrene, ethyl carbamate, furan derivatives, furfural, hydrazines, d-limonene,
psoralens, quercetin glycosides, safroleCRANBERRY SAUCE
furan derivatives
OR
PRIME RIB OF BEEF WITH PARSLEY SAUCEbenzene, heterocyclic amines, psoralens
VegetablesBROCCOLI SPEARS
allyl isothiocyanateBAKED POTATO
ethyl alcohol, caffeic acidSWEET POTATO
ethyl alcohol, furfuralBread
BOLLS WITH BUTTERacetaldehyde, benzene, ethyl alcohol, benzo(a)pyrene, ethyl carbamate, furan derivatives, furfural
DessertsPUMPKIN PIE
benzo(a)pyrene, coumarin, methyl eugenol, safroleAPPLE PIE
acetaldehyde, caffeic acid, coumarin, estragole, ethyl alcohol, methyl eugenol, quercetin glycosides, safroleFruit Tray
FRESH APPLES, GRAPES, MANGOS, PEARS, PINEAPPLEacetaldehyde, benzaldehyde, caffeic acid, d-limonene, estragole, ethyl acrylate, quercetin glycosides
BeveragesRED WINE
ethyl alcohol, ethyl carbamateCOFFEE
benzo(a)pyrene, benzaldehyde, benzene, benzofuran, caffeic acid, catechol, 1,2,5,6- dibenz(a)anthracene, ethyl benzene, furan, furfural, hydrogen peroxide, hydroquinone, d-limonene, 4-methyicatechol
TEAbenzo(a)pyrene, quercetin glycosides
JAMINE TEAbenzyl acetate
NATURALLY OCCURRING MUTAGENS AND CARCINOGENSFOUND IN FOODS AND BEVERAGES
ACETALDEHYDE (apples, bread, coffee, tomatoes)-mutagen and potent rodent carcinogen AFLATOXIN (nuts)-mutagen and potent rodent carcinogen; also a human carcinogen ALLYL ISOTHIOCYANATE (arugula, broccoli, mustard)-mutagen and rodent carcinogen ANILINE (carrots)-rodent carcinogen BENZALDEHYDE (apples, coffee, tomatoes)-rodent carcinogen BENZENE (butter, coffee, roost beef-rodent carcinogen BENZO(A)PYRENE (bread, coffee, pumpkin pie, rolls, tea)-mutagen and rodent carcinogen BENZOFURAN (coffee)-rodent carcinogen BENZYL ACETATE jasmine tea)-rodent carcinogen CAFFEIC ACID (apples, carrots, celery, cherry tomatoes, coffee, grapes, lettuce, mangos, pears, potatoes)-rodent carcinogen CATECHOL (coffee)-rodent carcinogen COUMARIN (cinnamon in pies)-rodent carcinogen 1,2,5,6-DIBENZ(A)ANTHRACENE (coffee)-rodent carcinogen ESTRAGOLE (apples, basil)-rodent carcinogen ETHYL ALCOHOL (bread, red wine, rolls)-rodent and human carcinogen ETHYL ACRYLATE (pineapple)-rodent carcinogen ETHYL BENZENE (coffee)-rodent carcinogen ETHYL CARBAMATE (bread, rolls, red wine)-mutagen and rodent carcinogen FURAN AND FURAN DERIVATIVES (bread, onions, celery, mushrooms, sweet potatoes, rolls, cranberry sauce, coffee)- (many are mutagens) FURFURAL (bread, coffee, nuts, rolls, sweet potatoes)-furan derivative and rodent carcinogen HETEROCYCLIC AMINES (roast beef, turkey)-mutagens and rodent carcinogens HYDRAZINES (mushrooms)-mutagens and rodent carcinogens HYDROGEN PEROXIDE (coffee, tomatoes)-mutagen and rodent carcinogen HYDROQUINONE (coffee)-rodent carcinogen D-LIMONENE (black pepper, mangos)-rodent carcinogen 4-METHYLCATECHOL (coffee)-rodent carcinogen METHYL EUGENOL (basil, cinnamon and nutmeg in apple and pumpkin pies)-rodent carcinogen PSORALENS (celery, parsley)-mutagens, rodent and human carcinogens QUERCETIN GLYCOSIDES (apples, onions, tea, tomatoes)-mutagens and rodent carcinogens SAFROLE (nutmeg in apple and pumpkin pies, black pepper)-rodent carcinogen
You MUST do the best engineering calculation you can
BUT if you cannot express it simplyPeople with think you dont understand
itAND THEY ARE PROBABLY
RIGHT
Example: Risk of a Space Probe
major risk:Probe (powered by Plutonium) reenters
the earth’s atmosphereburns up
spreads its plutonium widely over everyone
Causes an increase in lung cancer
3 Steps(1) What is the probability of reentry
(2) What is the distribution of Plutonium
(3) Compare with what we know
Probability of probe hitting the earth’s atmoshere in swing-by
Orbit calculatedcan be corrected.
No large correction (avoiding saboteur)
1 in 10,000,000
Russian workers in Ozersk --10 microCurie Pu(measurement in skeleton)Double risk of lung cancer)
Pu in atmoshere from bomb explosions leads to 30 picocurie in each of us
30,000 times less lung cancer of a heavy cigarette smoker.
This multiplies the risk of the sattelite hitting the earth
(P <10^-11)(Accurate calculation 10^-14)
If the distribution of fiber type, size and shapeis identical in the occupational epidemiological studies and in the environmental samples of interest, extrapolation to low doses is comparatively simple
Note that the incremental Risk can actually be greater than the simple linearity assumption of a
non-linear biological dose-response is assumed
Assumptions for animal analogy with cancer:
A man eating daily a fraction F of his body weight is as likely to get cancer (in his lifetime) as an animal eating daily the fraction f
of his body weight.
The main steps of the analysis of impact pathways(Courtesy A. Rabl).
DOSE
IMPA
CT
Dose-ResponseFunction
impact(e.g., cases of asthma due to increased
concentration of particulates)
DOSE-RESPONSE FUNCTION(or exposure-response function)
cost(e.g., cost of asthma)
ECONOMIC VALUATION
DISPERSION(e.g. atmospheric dispersion model)
emission(e.g., kg/yr of particulates)
increase in concentrationat receptor sites
(e.g., µg/m3 of particulatesin all affected regions)
SOURCE(specification of site and technology)