Decoy effect

In marketing, the decoy effect (or asymmetric dominance effect) is the phenomenon whereby consumers will tend to have a specific change in preference between two options when also presented with a third option that is asymmetrically dominated. An option is asymmetrically dominated when it is inferior in all respects to one option; but, in comparison to the other option, it is inferior in some respects and superior in others. In other words, in terms of specific attributes determining preferability, it is completely dominated by (i.e., inferior to) one option and only partially dominated by the other. When the asymmetrically dominated option is present, a higher percentage of consumers will prefer the dominating option than when the asymmetrically dominated option is absent. The asymmetrically dominated option is therefore a decoy serving to increase preference for the dominating option. The decoy effect is also an example of the violation of the independence of irrelevant alternatives axiom of decision theory.

Example

For example, if there is a consideration set involving MP3 players, consumers will generally see higher storage capacity (number of GB) and lower price as positive attributes; while some consumers may want a player that can store more songs, other consumers will want a player that costs less. In Consideration Set 1, two devices are available:

Consideration Set 1

	A	B
price	$400	$300
storage	30GB	15GB

In this case, some consumers will prefer A for its greater storage capacity, while others will prefer B for its lower price.

Now suppose that a new player, C, is added to the market; it is more expensive than both A and B and has more storage than B but less than A:

Consideration Set 2

	A	B	C
price	$400	$300	$450
storage	30GB	15GB	25GB

The addition of C—which consumers would presumably avoid, given that a lower price can be paid for a model with more storage—causes A, the dominating option, to be chosen more often than if only the two choices in Consideration Set 1 existed; C affects consumer preferences by acting as a basis of comparison for A and B. Because A is better than C in both respects, while B is only partially better than C, more consumers will prefer A now than did before. C is therefore a decoy whose sole purpose is to increase sales of A.

Conversely, suppose that instead of C, a player D is introduced that has less storage than both A and B, and that is more expensive than B but not as expensive as A:

Consideration Set 3

	A	B	D
price	$400	$300	$350
storage	30GB	15GB	10GB

The result here is similar: consumers will not prefer D, because it is not as good as B in any respect. However, whereas C increased preference for A, D has the opposite effect, increasing preference for B.

References

• J. Huber et al. (June 1982). "Adding Asymmetrically Dominated Alternatives: Violations of Regularity and the Similarity Hypothesis". The Journal of Consumer Research 9 (1): 90ff. doi:10.1086/208899. 
• Vedantam, Shankar (April 2, 2007). "The Decoy Effect, or How to Win an Election". The Washington Post. http://www.washingtonpost.com/wp-dyn/content/article/2007/04/01/AR2007040100973.html. Retrieved 2007-04-02. 
• National Public Radio (April 26, 2007). "Measuring 'the Decoy Effect' in Political Races - interview with Shankar Vedantam". NPR. http://www.npr.org/templates/story/story.php?storyId=9585221. Retrieved 2007-04-26.