What Is Contrast Bias? (Cognitive Bias)

Contrast Bias

Easy Definition of Contrast Bias: When ranking things, be sure to consider the whole group. You shouldn't rank something based on just one comparison.

Geeky Definition of Contrast Bias: Contrast Bias is the tendency to promote or demote something in a large grouping after a single comparison with one of its peers.

An Example of Contrast Bias

Gather your least attractive mates together and go on the pull

Average-looking people seem more attractive when alongside those who are less easy on the eye. Imagine an average-looking man was being scored for his looks. When judged independently, he might score 5/10. But, when judged alongside a less attractive person, his score would increase if the judge were suffering from Contrast Bias. And, it's likely the judge would be.

Contrast Bias is extremely common. In a bias-free world, the man would score 5/10 regardless of those around him. But we know it's not. So, if you're looking for love, it really is in your best interest to arrange a night out with a group of your not-so-aesthetically-pleasing friends. In effect, the average level of attractiveness of your group of friends is established as an anchor (see Anchoring Bias) against which observers make a relative judgement.

A Practical Application for Contrast Bias

Create a product that no one will buy and your sales will rocket

I love this sales technique. In his book Predictably Irrational, Dan Ariely offers a great example of how The Economist created an advert to force readers to make a comparison that influenced their buying decisions. At the start, The Economist presented the following advert:

Economist.com Subscription....................$59
(On-line access to all articles for one year)

Print and Web Subscription.....................$125
(1-year subscription to the printed edition and full on-line access)


This advert saw 68% of buyers go for the $59 product and 32% go for the $125 one. Not happy with how their advert was performing, they then presented the advert below. It's the same advert but with a "decoy" added.

Economist.com Subscription....................$59
(On-line access to all articles for 1 year)

Print Subscription...................................$125
(1-year subscription to the printed edition)

Print and Web Subscription.....................$125
(1-year subscription to the printed edition and full on-line access)


What they'd done is force the reader to make a comparison between the first $125 product and the second $125 product. Clearly, the second one was a much better offer. In the minds of the readers, that comparison trumped the real comparison they should have been making, i.e., the one with the $59 product. The sales then went:
  • 16% for the $59 product
  • 0% for the first $125 product (obviously)
  • 84% for the second $125 product
In other words, the decoy (the one in the middle) had caused a rise from 32% to 84% for the $125 product.

You can use this technique too. If you're selling two things and want people to buy your more expensive one, create a decoy which costs the same (or about the same) as your most expensive product but is obviously far poorer value for money. This will force people to make a comparison between your decoy and the most expensive product. That comparison will knock out the real comparison they should make between your cheapest and most expensive products.
Summary of Contrast Bias: If you think someone is ranking something wrongly after making a largely irrelevant comparison, tell him he's suffering from Contrast Bias.
The information on this page is taken from
"How To Get Your Own Way"
by Craig Shrives and Paul Easter.


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