Oddly Wired
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decision

You choose the middle option to avoid extremes.

A third, inferior option can make the other choices more attractive.

If you are choosing between a small, cheap item and a large, expensive one, adding a medium-priced item that is clearly worse than the large one makes the large one look like a bargain. You do not value the item itself; you value the comparison. Your preference is created by the menu.

Your choices are being steered by the options you reject.

Where this comes from

Study
Huber, Payne, and Puto (1982)
What the check found
This describes the 'decoy effect' or 'asymmetric dominance effect.' Huber, Payne, and Puto (1982) is the seminal paper identifying this phenomenon.
Confidence
Solid, with limits

Related

One of these every day, and every one names the study it came from. When a finding is contested, it says so.