Decoy Effect

What is it?

The decoy effect (also called asymmetric dominance) occurs when adding a third option changes preferences between the original two. The decoy is designed to be inferior to one option but not clearly comparable to the other. For example, if consumers are choosing between a small $3 popcorn and large $7 one, adding a medium at $6.50 makes the large seem like a great deal. The decoy (medium) is clearly worse than the large but not clearly comparable to the small—it makes the large "dominant" and increases its selection. The effect violates the principle of "independence of irrelevant alternatives" in rational choice theory: preferences between A and B shouldn't change because C is added. But humans aren't rational. We evaluate options relatively, and decoys manipulate the comparison set. Marketers use decoys in pricing strategies, subscription tiers, and product lineups. Real estate agents show an inferior property to make the target property more appealing. In negotiations, an extreme initial offer can make subsequent offers seem reasonable by comparison. Awareness of the decoy effect helps in recognizing when options are structured to manipulate choice, and in evaluating each option on its absolute merits rather than relative to cleverly positioned alternatives.