Independence of irrelevant alternatives

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Independence of irrelevant alternatives (IIA), also known as binary independence, the independence axiom, is an axiom of decision theory and economics describing a necessary condition for rational behavior. The axiom says that a choice between ${\displaystyle A}$ and ${\displaystyle B}$ should not depend on the quality of a third, unrelated outcome ${\textstyle C}$.

The axiom is deeply connected to several of the most important results in social choice, welfare economics, ethics, and decision theory. Among these results are Arrow's impossibility theorem, the VNM utility theorem, Harsanyi's utilitarian theorem, and the Dutch book theorems.

Violations of IIA are called menu effects or menu dependence.