Step 6 involves assessing the probability of an outcome in the interval centred on the pessimistic outcome scenario value. Given an estimated 0.2 probability for the interval centred on the optimistic outcome scenario value and the complementary nominal 90 or 10 percentile interpretation of the pessimistic outcome scenario, 0.3 is a reasonable expectation, rounding up to reflect the usual asymmetry of both threat and opportunity distributions. In general there is more scope for things to go badly than there is for things to go well relative to expectations. An estimate of 0.2 may be preferred, and 0.4 is a possibility, but 0.1 would be a cause for query. As in the context of the optimistic outcome probability, the process is efficient and quick for participants of even modest experience, with simplicity driven by the scenario interpretations.
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