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The distinction between validation
(forecast system’s characteristics) and verification
(forecast system’s predictive skill) is as relevant in
probabilistic as in deterministic forecasting. As with the
deterministic forecasting system, probability verification
can address the accuracy (how close the forecast
probabilities are to the observed frequencies), the skill
(how the probability forecasts compare with some reference system)
and utility (the economic or other advantages of the
probability forecasts).
Sceptics of probability forecasts argue that
forecasters might exaggerate uncertainty “to cover their
backs”. However, as will be shown, the verification of
probabilistic forecasts takes the “reliability” of the
probabilities into account and will detect any such misbehaviour.
Indeed, one of the most used verification scores, the Brier score,
is mathematically constructed in a way that encourages forecasters
to state the probability they really believe in, rather than some
misperceived “tactical” probability.
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