levels of uncertainty hauke riesch dept. of social sciences, media and communications, brunel...

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Levels of uncertainty Hauke Riesch Dept. of Social Sciences, Media and Communications, Brunel University London [email protected]

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Levels of uncertainty

Hauke RieschDept. of Social Sciences, Media and Communications, Brunel University

London

[email protected]

Two traditions of risk

Risk as a potential future hazard (e.g. Knight, Beck, Giddens)

Risk as a clearly defined measure ofProbability of an event x severity of the outcome

of the event

Quantifiable vs unquantifiable uncertainty

“The essential fact is that ‘risk’ means in some cases a quantity susceptible of measurement, while at other times it is something distinctly not of this character; and there are far-reaching and crucial differences in the bearings of the phenomena depending on which of the two is really present and operating. [. . .] It will appear that a measurable uncertainty, or ‘risk’ proper, as we shall use the term, is so far different from an unmeasurable one that it is not in effect an uncertainty at all” (Knight 1921)

Risk = uncertainty x outcome

Problems in how exactly the two are defined, especially if we want to do a comparison of numbers in a formal risk assessment.

Mapping risk:

Funtowicz and Ravetz's “postnormal science”

Mapping risk:Renn, O., & Klinke, A. (2004). Systemic risks: a new challenge for risk management.

EMBO reports, 5(1S), S41-S46.

Mapping risk:Stirling, A. (2007). Risk, precaution and science: towards a more constructive policy debate. EMBO

reports, 8(4), 309-315.

Mapping risk: Our attempt

What is interesting about risk?

Why are we uncertain? Who is uncertain? How is uncertainty represented? Responses to uncertainty Understanding uncertainty What exactly are we uncertain about?•(Spiegelhalter and Riesch, 2011)

Why are we uncertain? Epistemic vs. Aleatoric uncertainty

Epistemic (don't know): we are uncertain because we have insufficient knowledge (e.g. is there is a Starbucks in Hayes?)

Aleatoric (can't know): We are uncertain because of the experimental set up (will I win the lottery?)

Who is uncertain?

Different people respond differently to uncertainty:

- “White male” effect •(Finucane, M. L., Slovic, P., Mertz, C. K., Flynn, J., & Satterfield, T. A. (2000). Gender, race, and perceived risk: The 'white male‘ effect. Health, Risk & Society, 2(2), 159-172.)

- Technology Policy: different groups of stakeholders will have different views and reactions to a technological risk: Should there be a waste incinerator in Shepperton?

How is uncertainty represented?What are the risks of eating bacon sandwiches? Riesch, H., & Spiegelhalter, D.

J. (2011).

Risk of eating more than 500g of processed meat a day over a lifetime was quoted as 20% more than if we don't eat any processed meat.

What does that mean?

http://understandinguncertainty.org/files/animations/RiskDisplay1/RiskDisplay.html

Responses to uncertainty

Risk Perception and the psychometric paradigm

Since the 1950s, psychologists have tried to find out about people's unconscious perceptions of risk, so that we have a better understanding of where people act irrationally and where we can correct people's understanding of risk in a way that makes them behave rationally (Kahnemann, Twerski, Slovic etc.)

Responses to uncertainty

On a societal level, the literature on our responses to uncertainty is covered by the risk society theses of Ulrich Beck and Anthony Giddens.

Here, the issue is not so much about the nature of the risk as such, or even whether the risks are real or not, but with the role that an increasing awareness of risk plays within late modern society. In particular, they describe the intuitive pessimistic induction through which people have come to realize (or at least believe) that there are always unexpected uncertainties and the possibility of things going horribly wrong with any possible new technological invention (the ‘‘unintended consequences of modernity’’).

Responses to uncertainty

Risk society

Thus, as society has become more reflexive about its own technological achievements, the awareness of risk has become a more powerful driver of social forces than it was previously when risks were more perceived as due to intangible forces of nature rather than consequences of our own society, and therefore modern Western society’s response to risk has become qualitatively different to what it was before.

Object of uncertainty: What are we uncertain about?

Brian Wynne: Categorising risksRisk: outcomes and the probabilities are well

known and quantifiable.Uncertainty: ‘‘we know the important system

parameters, but not the probability distributions”

Ignorance: ‘‘This is not so much a characteristic of knowledge itself as of the linkages between knowledge and commitments based on it’’

Indeterminacy: questions the assumption on the causal chains and networks themselves

Object of uncertainty: What are we uncertain about?

Spiegelhalter and Riesch (2011)

Wynne's classification somewhat unintuitive and difficult to explain. We have instead proposed a five-fold classification.

There are different levels of uncertainty, i.e. we have a probability as a final measure, but we may be uncertain about how we arrived at the probability.

Objects of uncertainty

Illustration with snooker balls in a bagLevel 1: uncertainty in the outcome: we know the

model, we know the parameters, the uncertainty then is predicted by the laws of probability.

A bag with 10 balls, 5 red and 5 black. What is the probability that we draw a red ball?

Objects of uncertainty

Level 2: Uncertainty about the parameters

A bag with 10 balls, but I haven't specified how many are black and how many are red. What is the probability that we draw a red ball?

Objects of uncertainty

Level 3: Uncertainty about the model:

I have two bags, one with 10 balls that are either red or black, and one with 5 balls that are either red or black, and I don't know which one I pick.

What is the probability that I draw a red ball?

Objects of uncertainty

Level 4: Uncertainty over our assumptions

I have a bag with 10 balls, either red or black. But I may be lying to you and all the balls in the bag are green.

What is the probability that I draw a red ball?

Objects of uncertainty

Level 5: unknown unknowns:

I have a bag...

Levels of uncertainty and bacon sandwiches

Level 1: the risk quoted by the WCRF report (20% increase)

Level 2: the uncertainty that results from the parameters: how certain are the WCRF that the 20% figure is correct? The report itself provides an error that acknowledges that there is uncertainty over their results (based on their studies, they report a “strong” indication that the risks are a 20% increase)

Levels of uncertainty and bacon sandwiches

Level 3: the uncertainty that results from the WCRF choosing the right model: could other ways of modelling the risks be better?

- alternative health practitioners have criticised the report because they don't recognise the scientific methods the WCRF used as valid. What is the probability that they are correct?

Levels of uncertainty and bacon sandwiches

Level 4: uncertainty over acknowledged assumptions

Are the WCRF scientists competent? Are they trustworthy? What is the probability of those?

Level 5: Unknown unknowns:Might there not be anything else wrong with the

WCRF report that we didn't think of?

Spiegelhalter, DJ. and Riesch, H. (2011), Don't know, can't know: Embracing deeper uncertainties when analysing risks, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 369 (1956) : 4730- 4750 Download publication

Riesch, H. (2012) , Levels of Uncertainty. In: Roeser, S. , Hillerbrand, R. , Sandin, P. and Peterson, M. eds. Handbook of Risk Theory: Epistemology, Decision Theory, Ethics, and Social Implications of Risk. Springer 87- 110

Riesch, H. and Spiegelhalter, DJ. (2011) , 'Careless pork costs lives': risk stories from science to press release to media, Health Risk and Society 13 (1) : 47- 64

Upham, P. , Riesch, H. , Tomei, J. and Thornley, P. , (2011), The sustainability of forestry biomass supply for EU bioenergy: A post-normal approach to environmental risk and uncertainty, Environmental Science and Policy 14 (5) : 510- 518