21  Expert Political judgment

In Expert Political Judgment: How Good Is It? How Can We Know?, Tetlock (2005) reports on a project in which he asked a range of experts to predict future events. With the need to see how the forecasts panned out, the project ran for almost 20 years.

The basic methodology was to ask each participant to rate three possible outcomes for a political or economic event on a scale of 0 to 10 on how likely each outcome is (with, assuming some basic mathematical literacy, the sum allocated to the three options being 10). An example question might be whether a government will retain, lose or strengthen its position after the next election. Or whether GDP growth will be below 1.75 per cent, between 1.75 per cent and 3.25 per cent, or above 3.25 per cent.

Once the results were in, Tetlock scored the participants on two dimensions - calibration and discrimination. To get a high calibration score, the frequency with which events are predicted needs to correspond with their actual frequency. For instance, events predicted to occur with a 10 per cent probability need to occur around 10 per cent of the time, and so on. Given experts made many judgments, these types of calculations could be made.

To score highly on discrimination, the participant needs to assign a score of 1.0 to things that happen and 0 to things that don’t. The closer to the ends of the scale for predictions, the higher the discrimination score. It is possible to be perfectly calibrated but a poor discriminator (fence sitter) through to a perfect discriminator (only using the extreme values correctly).

Figure 21.1: What good calibration and discrimination look like (Figure 2.3 from Tetlock (2005))

Tetlock’s analysis revealed that:

Figure 21.2: Expert calibration (Figure 2.6 from Tetlock (2005))

The one dimension where forecast accuracy was differentiated is on what Tetlock calls the fox-hedgehog continuum (borrowing from Isiah Berlin). Hedgehogs know one big thing and aggressively expand that idea into all domains, whereas foxes know many small things, are skeptical of grand ideas and stitch together diverse, sometimes conflicting information. Foxes are more willing to change their minds in response to the unexpected, more likely to remember past mistakes, and more likely to see the case for opposing outcomes. Foxes outperformed on both measures of calibration and discrimination.

What is it about foxes and hedgehogs that leads to differences in performance? Among other reasons, Tetlock identified the following: