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Communicating risk

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Communicating risk

  1. 1. Communicating Uncertainty Andy Hart Food and Environment Research Agency, York andy.hart@fera.gsi.gov.uk BSA Science Communication Conference, 1 May 2014
  2. 2. Why communicate uncertainty? Red River Flood, Grand Forks USA, 1997 • Levee height: 51 feet • River height prediction: 49 feet • Uncertainty: plus or minus 9 feet 51 49 ±9 After: Nate Silver, The Signal and the Noise, 2012
  3. 3. Why communicate uncertainty? Red River Flood, Grand Forks USA, 1997 • Levee height: 51 feet • River height prediction: 49 feet • Uncertainty: plus or minus 9 feet • Actual flood height: 54 feet 51 49 ±9 After: Nate Silver, The Signal and the Noise, 2012
  4. 4. Why communicate uncertainty? Red River Flood, Grand Forks USA, 1997 • Estimated damages: ca. $3.5 billion 51 49 ±9
  5. 5. Why communicate uncertainty? ‘Credibility requires trust… …trust requires openness… …openness requires recognition of uncertainty’ (Phillips Report on BSE, 2000)
  6. 6. What to communicate? • What information is needed to communicate uncertainty?
  7. 7. Reasons for uncertainty • Red River Flood height affected by: − Temperature (snow melt) − Rainfall − Bridges, sandbags etc. (retard flow) − Volume of water downstream − Extrapolation beyond previous data Reasons are important, but not enough 51 49
  8. 8. Confidence in predictions? • 12th April 2013 – US Intelligence reports ‘moderate confidence’ that North Korea has nuclear weapons • They say: ‘Moderate confidence generally means the information is interpreted in various ways, we have alternative views, or the information is credible and plausible but not corroborated sufficiently to warrant a higher level of confidence’ Qualitative expressions of confidence are not enough 51 49
  9. 9. The range of plausible outcomes • Tells you what might happen • But not how likely that is • Okay if all the outcomes are okay • Not enough if bad outcomes are possible but costly to avoid or mitigate  Also need information on the relative likelihoods of different outcomes 51 49 ±9
  10. 10. The range of plausible outcomes • Also need information on the relative likelihoods of different outcomes TV forecasts for Hurricane Irene, 2011
  11. 11. 299600 299700 299800 299900 300000 1870 1890 1910 1930 1950 Measuredspeedoflight(km/sec) Confidence intervals Include information on likelihood but only for uncertainties that have been quantified Historical measurements of the speed of light, ± measurement error (1 standard deviation) After Henrion and Fischoff, 1986 Generally accepted value (1986)
  12. 12. Confidence intervals • Confidence intervals from data or modelling only express uncertainty quantified in the data or model  Need to: − say which uncertainties have been quantified − identify any additional uncertainties − indicate their potential impact on the range and likelihood of alternative outcomes − acknowledge any deep uncertainties for which this is not possible
  13. 13. Additional uncertainties • Impact of additional uncertainties e.g. Bank of England fan charts take account of additional uncertainties when forecasting inflation % increase on prices a year earlier past future
  14. 14. Qualitative expressions of likelihood? • The same word means different things to different people • Words are not enough 51 49 ±9 Macleod & Pietravalle
  15. 15. Subjective probabilities “Some of our intelligence officers thought that it was only a 40 or 30% chance that Bin Laden was in the compound. Others thought that it was as high as 80 or 90%. At the conclusion of a fairly lengthy discussion where everybody gave their assessments I said: this is basically 50-50.” Barack Obama speaking on ‘Bin Laden: Shoot to Kill’, Channel 4, 7 September 2011
  16. 16. Words with quantitative meaning • E.g. IPCC Likelihood scale: • Verbal definitions just transfer the problem 51 49 ±9
  17. 17. Words with quantitative meaning ‘The UNEP report puts the average global cooling that could be achieved with black-carbon control measures at 0.3 watts per square metre… ... the range of possible effects runs from twice that much to nothing at all ...there is even an outside chance that the proposed action could lead to a little warming... ...though if that were the case the actions on ozone would still provide a net cooling for the actions as a whole…’ NASA GSFC The Economist, 19 Feb. 2011
  18. 18. Deep uncertainty • If it’s not possible to quantify likelihood even approximately then it is misleading to use undefined verbal expressions • Indicates presence of deep uncertainties − describe them − explain the prediction is just one possibility − if nothing can be said about the range and/or likelihood of other outcomes then say so 51 49
  19. 19. What is being done about it • Who are the relevant authorities? • What are they doing to decrease the chance of adverse outcomes? • What are they doing to monitor the situation? • What contingency plans do they have? • What options can others consider? 51 49 ±9
  20. 20. Outcomes are always uncertain express confidence in the chosen strategy (if warranted) but acknowledge the outcome is still uncertain 51 49 ±9
  21. 21. Summary Information needed for communicating uncertainty: • Reasons for uncertainty • Range of plausible outcomes • Likelihood of adverse outcomes − As quantitative as possible • Nature of deep uncertainties, if present • What is being done about it? If this information isn’t provided, ask for it! 51 49 ±9

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