Decoy Effect

We compare things to each other, but we also tend to focus on things that are easily comparable and avoid those that are not. For example, if you have two traits, A & B, and you have three objects, two of which vary along the dimension of A (an “A” and an inferior “A-”). People will tend to pick the “A” version without comparing the version that varies positively along the B trait. In essence, introducing (-A), the decoy, creates a simple relative comparison with (A), and hence makes (A) look better, not just relative to (-A), but overall as well. As a consequence, the inclusion of (-A) in the set, even if no one ever selects it, makes people more likely to select A(Ariely 2010).