Context effects in multi-alternative choice demonstrate that preferences are not fixed properties of options but depend on the set of available alternatives. Three classic effects — similarity, attraction, and compromise — each violate the principle of Independence from Irrelevant Alternatives and pose fundamental challenges to simple choice models.
The Three Classic Effects
Attraction: adding dominated D near A increases P(A)
Compromise: making A the middle option increases P(A)
The similarity effect occurs when a new option similar to an existing one draws disproportionately from that option's share. The attraction effect (or asymmetric dominance) occurs when adding a clearly inferior "decoy" option increases preference for the option that dominates it. The compromise effect occurs when an option's share increases when it becomes the middle or compromise option in the set.
Theoretical Accounts
These effects have motivated several formal models: EBA accounts for the similarity effect; Decision Field Theory accounts for all three through its attention-switching dynamics; the Leaky Competing Accumulator reproduces them through lateral inhibition. The attraction effect, in particular, has been influential because it demonstrates that adding an objectively irrelevant option (one no one would choose) can change which of the original options is preferred — a powerful demonstration of context-dependent preference construction.