Why the digits in an address you just typed sway your bid

Ariely, Loewenstein, and Prelec asked participants to write the last two digits of their Social Security number before bidding on a bottle of wine. Those with high final digits bid sixty to one hundred and twenty percent more than those with low digits. The Social Security number bore no relation to the wine; the digits became the anchor anyway.

What everyone sees

Bidders believe their offers reflect their genuine valuation of the wine. When told that the digits influenced their bids, most express disbelief or insist they would have bid the same without the priming step. The two tasks feel categorically unrelated.

What is actually happening

Ariely and colleagues’ arbitrary-coherence research showed that even random numbers serve as anchors for subsequent numerical judgements, because the brain uses any accessible figure as a starting point. Tversky and Kahneman’s anchoring-and-adjustment heuristic adds that adjustments from an anchor are typically insufficient, so the final bid drifts toward the primed digits regardless of their irrelevance.

Why it stays hidden

The prime hides because the digits feel like a separate, completed task. The participant mentally closes the “address” step before opening the “bidding” step, unaware that the numbers from the first step are still active in working memory and contaminating the second. The anchor crosses the task boundary invisibly.