Communicating and evaluating probabilities

David Spiegelhalter

MRC Biostatistics and Statslab

CSI day: September 2011

With thanks to Mike Pearson and Ian Short

Summary • Visualisations • Met Office experiment• Scoring rules for a quiz

Spiegelhalter DJ, Short I and Pearson MP (2011) Visualisation of uncertainty about the future. Science 333, 1393-1400

Kickoff.co.uk

“Cone of Uncertainty” for hurricane warnings

2011: NBC News for Hurricane Katia

‘Possible futures’

metaphor

William Hill 1st June 2011

Quantifying your ignorance

• Think whether you prefer (A) or (B) for each question

• Then think of how confident you are with your answer

• Give your confidence a number 5 to 10

• Score yourself when you hear the correct answer

A short quiz

1. Which is higher, A) the Eiffel tower, B) Canary Wharf? A (324m vs 235m)2. Who is older, A) Prince William or B) Kate Middleton ? B (Born 21/6/82 vs 9/1/82)3. In the IMDB rankings (20/05/2011), which film comes higher, A) Toy Story 3 or B) WALL.E? A (34th vs 50th)4. Which is larger, A) Belgium or B) Switzerland? B (30 vs 41 000 sq km)5. Which is bigger, A) Venus B) Earth? B (6051 vs 6371 km radius)6. Who died first, A) Beethoven or B) Mozart? B (1827 vs 1791)

Online quiz

Scoring the quiz

Current issue: how to break down someone’s total score

Cochrane video