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Poisson’s formula is a method of calculating the possibilities of recurrence of an event, based on a number of occurrences in the past.
For this listing, the time should be adjusted so that the number of occurrences is in the range 3 to 12. The range could be extended upwards if required, but 2 has been omitted as it would mean an unreliably small sample.
The formula here is applied with a correction factor but that will not distort the results, since the same percentage is applied to all answers, thus keeping them in the same proportion.