Margaret, whom we described as a well-calibrated forecaster because she rated 500 events as 60% likely, and 300 of those events did happen. This result may not be as impressive as it seems. If Margaret is a weather forecaster who always predicts a 60% chance of rain and there are 300 rainy days out of 500, Margaret’s forecasts are well calibrated but also practically useless. Margaret, in essence, is telling you that, just in case, you might want to carry an umbrella every day. Compare her with Nicholas, who predicts a 100% chance of rain on the 300 days when it will rain, and a 0% chance of
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