No.8 of 36 Base Rate Fallacy

No.8 of 36 Base Rate Fallacy

A phenomenon known as base rate fallacy illustrates how people can sometimes jump to inappropriate conclusions, with significant consequences.

Base rate fallacy, or base rate neglect, is the tendency for people to mistakenly judge the likelihood of a situation by not taking into account all relevant data. Don't think "99% accurate" means a 1% failure rate. There's far more to think about before you can work out the failure rate.

What is Base Rate Fallacy?

The base rate fallacy is a common cognitive error that tends to affect our reasoning in everyday situations.

This bias tends to arise when we encounter unfamiliar or complex data, and it causes us to rely too heavily on the first piece of information that we come across. For example, when going shopping, many people will base their purchasing decisions on some initial spark of interest or attraction rather than considering broader trends and statistics.

As a result, they may end up buying items that they do not actually need or want, simply because they are being swayed by aggressive marketing techniques or flashy packaging.

Base rate fallacy illustration
[Image source]

Examples the Base Rate Fallacy in-store

Lots of brands exploit the Base Rate Fallacy on their packaging.

When something says "50% extra free" if you think half of what you're looking at is free, then you've committed the Base Rate Fallacy.

For example, when you buy six cans of Coke labelled "50% extra free," only two of the cans are free, not three - only a third (33%) of what you're looking at is free.

This is because the original pack had four cans, and 50% of the original amount is two cans.

If you thought 3 of the cans were free, then you failed to account for an earlier premise i.e., there were four cans originally, and you committed the Base Rate Fallacy.

Applying the Base Rate Fallacy in marketing

There are a lot of opportunities relating to base rate fallacy in-store and online. But you need to be careful not to confuse shoppers or have them distrust you.

For this reason, here are 3 tactics to employ at all times:

Whiter than white

It's better to be honest and true, but unfortunately, much in-store promotional activity exploits base rate fallacy. So instead of you appearing to offer a weaker deal (because you are too honest), highlight where your competitors are exploiting this bias.

Don’t be too white!

If there is a better way to communicate number or brand aspects then do so. In other words, being totally honest is good, but don’t be over-honest. Communicate with shoppers in the most effective but ethical ways possible, utilising base rate fallacy for good, not bad.

Base rate in context

Provide shoppers with context so that your base rate examples look as attractive and appealing as possible. For example, “Buy 3 get 1 free” - whisper buy 3 (that’s the instruction or order) and shout get 1 free!

The future of the Base Rate Fallacy

Due to the current accountant lead nature of retail, base rate fallacy is a very, very big opportunity and potential problem. Examine the numbers you communicate to shoppers and then look at then in relation to base rate fallacy.

Could you be doing things better? Are you misleading shoppers?

Found this blog post useful?

Why not get a FREE brand review to boost your brand communications...

About Phillip Adcock

My name is Phillip Adcock: I have more than 30 years of human behavioural research and analysis, and have developed a unique ability to identify what it is that makes people psychologically and physiologically 'tick'.

Would you like to know more about how shoppers and consumers think? Download my FREE guide now. Alternatively, check out, where there are more FREE downloads available there. Or why not simply email me with what's on your mind?

If you think there is value in this article then please, please share it, thank you.

Phillip Adcock

Phillip Adcock CMRS
Psychology & Behaviour
Change Consultant

Phillips Signature

Explore our Brainsights

Behavioural Science & Shopper Psychology Workshops

Are you ready to unlock the power of Behavioural Science & transform your business with Shopper Psychology-based insights?

Read Story

Coca-Cola Zero Sugar Cans get Revamp

Coca-Cola Zero Sugar cans are to be revamped with an alleged ‘sleek’ smooth new look. But why has Coke done this? Here’s some interesting science...

Read Story

Get the latest brainsights straight to your email box

We will never share your email address with third parties.
By subscribing you agree to with our Privacy Policy and provide consent to receive updates from our company.