I thought Sunak would be PM: here's what I got wrong

Dominic Cummings is not the only person who has read Superforecasting, the book by Philip Tetlock and Dan Gardner.

- JOHN RENTOUL

I read it when it was published seven years ago, and thought it had important insights that would be useful in politics.

The book cites a wonderful example of hindsight bias. Tetlock asked experts in 1988 to put a percentage on the chance that the Communist Party would lose its monopoly on power in the Soviet Union in the next five years. Three years later, the Soviet Union was dissolved: "So in 1992-93 I returned to the experts, reminded them of the question in 1988, and asked them to recall their estimates. On average, the experts recalled a number 31 percentage points higher than the correct figure.

"So the expert who thought there was only a 10 per cent chance might remember herself thinking there was a 40 or 50 per cent chance. There was even a case in which an expert who pegged the probability at 20 per cent recalled it as 70 per cent - which illustrates why hindsight bias is sometimes known as the 'I knew it all along' effect."

I vowed at the time to resist the "I knew it all along" effect and to apply the lessons of Tetlock and Gardner's research to my own writing. One lesson above all: good forecasters go back over their old predictions honestly, and analyse why they got them wrong in an attempt to learn from their mistakes.