Sure-thing principle
In decision theory, the sure-thing principle states that a decision maker who would take a certain action if he knew that event E has occurred, and also if he knew that the negation of E has occurred, should also take that same action if he knows nothing about E.
The principle was coined by L.J. Savage:
He formulated the principle as a dominance principle, but it can also be framed probabilistically. Richard Jeffrey and later Judea Pearl showed that Savage's principle is only valid when the probability of the event considered is unaffected by the action. Under such conditions, the sure-thing principle is a theorem in the do-calculus. Blyth constructed a counterexample to the sure-thing principle using sequential sampling in the context of Simpson's paradox, but this example violates the required action-independence provision.
The principle is closely related to independence of irrelevant alternatives, and equivalent under the axiom of truth. It is similarly targeted by the Ellsberg and Allais paradoxes, in which actual people's choices seem to violate this principle.
