A probability needs an outcome set

A 30% number sounds precise until you ask: 30% of what, by when, and under which definition?

A probability is tied to an outcome set. Change the set and the number may describe a different question.

Name the denominator

Write the possible outcomes, the time window, the data source, and the rule that separates one result from another. Make sure the cases are mutually exclusive and cover the question you intend to answer.

A rate during a period, a count by a deadline, and a cumulative total can all receive different probabilities even when the headline sounds identical.

Check the payout against the question

Confirm that a winning share represents the outcome you estimated and that the payment does not hide extra cases. A neat formula cannot fix a mismatch between the estimate and the contract.

Keep the plain-language question next to the calculation so a later review can see what the percentage meant.

Stress the boundary cases

Test ties, missing data, revisions, and events that happen just before or after the cutoff. Those edge cases often reveal that the denominator was never written down.

The useful question is not whether the percentage looks reasonable. It is whether every part of the number points to the same outcome set that the market will resolve.

Further reading: Prices and order books · Resolution rules · Current fees.

Explore the markets: Open Polymarket (referral link).