The decoy effect — also called asymmetric dominance — occurs when a third option is added that is clearly inferior to one of two original choices but only slightly worse than the other. Nobody chooses the decoy. Its purpose is to shift the comparison frame so the target option looks obviously better.
In 1992, economist Joel Huber ran a study on consumer choice. He gave people two options for a beer: a cheap one and a premium one. Half of them chose each. Then he added a third option: an even cheaper, lower-quality beer. This new option was not attractive to anyone -- but its presence made the original cheap beer look better by comparison. Suddenly, significantly more people chose the premium option. The cheap beer had become the decoy.
The decoy effect -- also called asymmetric dominance -- works when a third option is added that is clearly worse than one of the original two in almost every way, but only slightly worse than the other. It does not attract buyers. What it does is shift the comparison. It makes the option it is close to look better by being nearly as good, and it makes the option it is far from look much more attractive by contrast.
You have felt this in real life. The medium popcorn at the cinema is $5. The large is $5.50. The small is $4.50. Nobody wants the medium -- but it makes the large look like an obvious deal. The small is the cheap option, the medium is the decoy, and the large is the target. The pricing is not arbitrary. It is engineered to funnel you to the large.
“Humans rarely choose things in absolute terms. We focus on the relative advantage of one thing over another.”
— Dan Ariely, Predictably Irrational, 2008
The demo below lets you choose a subscription plan -- first with two options, then with three. The plans and prices are identical in both versions. The only thing that changes is the presence of a decoy. Notice how differently the choice feels, and which option you are drawn to, in each scenario.
A genuine trade-off: $9 with limitations vs $29 with everything. Neither feels obviously right.
Standard at $25 gets you analytics but no API. Pro at $29 gets you everything. For just $4 more the upgrade is obvious -- that is the decoy at work.
The Standard plan at $25 is the decoy. It is priced close enough to Pro ($29) that the gap feels small, but it lacks API access, has project limits, and offers worse support. The comparison makes the $4 difference feel negligible. Before the decoy, $29 vs $9 felt like a significant jump. With the decoy, $25 vs $29 reframes the Pro upgrade as a minor cost for a major gain.
Dan Ariely documented the decoy effect in a famous real-world case. The Economist magazine offered three subscription options: Web only at $59, Print only at $125, and Web + Print at $125.
The print-only option at $125 is the decoy. Nobody in their right mind would pay the same price for print alone when web + print is available for the same money. Ariely surveyed MIT students: 84% chose web + print, 16% chose web only, and nobody chose print only. Then he removed the print-only option. Without the decoy, the choice shifted dramatically: 68% chose web only and only 32% chose web + print. The same product, the same price -- but removing the decoy cost the magazine a huge slice of its premium subscribers.
The print-only option at $125 is obviously worse than web + print at the same price. It is dominated. But its presence makes web + print feel like an unmissable deal -- you are getting more for the same money. Without it, web + print at $125 sits next to web-only at $59. Now it looks expensive. The decoy changed the frame of the comparison, not the product.
Like most of the tools in behavioural design, the decoy effect can be used honestly or manipulatively. The honest version: you have a product tier you genuinely want most users to choose because it is the best fit for most use cases. Adding a decoy that makes that tier look like the right choice is a nudge toward a recommendation -- not deception, because the product is genuinely what you are steering toward.
The manipulative version: the decoy is used to steer users toward a higher-margin tier they do not need, by making an inflated price look reasonable by comparison. Or the decoy itself is presented as a real option -- a plan that is technically purchasable but designed only to make another look good, with no intention of the decoy ever delivering value. If a user bought the decoy and felt deceived by what they got, the line has been crossed.
The test is the same as always: would users endorse the design decision if they understood it? A decoy that helps users find the right plan for their needs is a design tool. A decoy that tricks users into overspending is manipulation.
Huber, J., Payne, J. W., & Puto, C. (1982). Adding asymmetrically dominated alternatives. Journal of Consumer Research, 9(1), 90--98. Ariely, D. (2008). Predictably Irrational. HarperCollins. Simonson, I. (1989). Choice based on reasons: The case of attraction and compromise effects. Journal of Consumer Research, 16(2), 158--174.