Reference Classes

6 pages on this site touch on this topic.

• Base rate — How common something is in a relevant population or time period, before taking the specific case in front of you into account at all.
• Base rates: how common is this, really? — The most under-used number in any coincidence story is how often the 'surprising' thing happens anyway, to someone, without any special explanation.
• How to evaluate a coincidence claim — A twelve-step method for weighing a striking coincidence, from writing down the exact claim to stating plainly what remains unresolved.
• Probability is a model, not a verdict — Why a probability is always a statement about a chosen model and reference class, not a fact about a unique event — worked through the birthday problem.
• Reference classes: compared with what, exactly? — Every probability judgment implicitly compares an event to a class of similar events — and changing that class can change the answer without any new evidence.
• Reference-class worksheet — A practical worksheet for step 6 of the evaluation method: stating explicitly which comparison group a coincidence's probability is measured against.