Check whether a third option is changing your view of the original two

If a new option makes you change your preference between existing options, ask whether the new option should have that power.

Why it works

Rational preference requires independence of irrelevant alternatives (IIA): if you prefer A to B, adding C should not change that preference unless C provides genuinely new information about A or B. The decoy effect shows IIA is routinely violated; recognizing the violation in real time — "wait, why did that new option change how I see the original two?" — activates the deliberate reasoning needed to restore stable preferences.

How to do it

1. When a new option enters a decision (a competitor, a third candidate, an alternative offer), notice whether it changes your view of the existing options.
2. Ask: "Does this new option provide new information about the original options — or does it only change what looks good by comparison?"
3. If only comparison, remove the new option from the frame and restore your pre-existing preference order.
4. Only update your preference if the new option reveals genuinely new information (e.g., it exists, which means the price point is possible).

Evidence

The IIA violation is central to the decoy effect literature (Huber et al., 1982) and to Sen’s work on rational choice. The IIA check is a decision hygiene practice grounded in decision theory; direct evidence for the correction practice is mechanistic. (mechanistic)

In some cases, adding a third option does provide genuine information (it proves a certain quality level is feasible, or it reveals market pricing) — not every IIA violation is a bias.

Sources

• Huber, Payne & Puto (1982), Adding asymmetrically dominated alternatives, Journal of Consumer Research

Common mistake

Treating any preference change after adding an option as automatically irrational — the key is whether the new option carries genuine new information about the original options.