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Similarity Heuristic

Written by: Francisca Alho

From: Maputo, Mozambique

Edited by: Anna Kissajikian

As we all know, humans are lazy. I mean, you’re probably reading this while sitting or laying down, and we don’t blame you, life’s tough! We make all sorts of excuses to do as little work as possible, but did you know this also happens subconsciously, in our brains? 

This is where the idea of humans being cognitive misers comes from. We make a minimal effort to think, and expect maximum results. By creating ‘mental shortcuts’, for making these speedy choices and judgements, we are using what are called cognitive heuristics or biases. 

Hopefully, by the end of this article, you’ll have a deeper understanding of these, specifically the similarity heuristic. 

The similarity heuristic is considered a subset of the representativeness heuristic, which is used by decision-makers to judge the likelihood that an instance is a member of one category rather than another by the degree to which it is similar to others in that category. 


So now let’s look at a study. There’s no better way to understand something than by scientifically proving it, am I right? 

In 1974, Israeli philosopher Bar-Hillel, conducted study with the aim of better understanding this concept of similarity-based mental shortcuts. 

In order to do this, he:

  • Showed 76 undergraduates triples of bar graphs, Left (L), Middle (M), and Right (R). 

  • They were split up into three groups: similarity, likelihood of populations, likelihood of samples group.  

  • The similarity group, judged whether M was more similar to L or R.

  • The likelihood of populations group was told that M represented a sample that might have been drawn from either population L or R. They judged which population M was more likely to come from.

  • The Likelihood of samples group was told that M represented a population that might have generated either sample L or R. They judged which sample was more likely to be generated from M. 

Bar-Hillel predicted that if the similarity heuristic is used, all three judgments would coincide. He systematically designed the materials so that this coincidence could easily be observed. 


The results revealed that all 3 groups gave essentially the same responses. In particular, the likelihood judgments were closer to the similarity judgments than to the correct likelihoods, which supported Bar-Hillel’s hypothesis that both similarity and likelihood judgments would be strongly influenced by rank order. 

Real-life example

The similarity heuristic happens when people form judgments in current situations based on similarities it shares with preceding experiences or prototypes of these situations. When buying a snack, if one finds similar types of snacks as previously enjoyed they are most likely to buy it.

Another example might be when you’re interested in purchasing a new book. If the novel has a similar plot or genre to novels previously appreciated, your decision might be positively influenced by this bias.

How to avoid it

How can these be avoided?

  • Develop insight and awareness. Make sure to take time when thinking, in order to truly exercise your conscious mind by using type 2 or “rational” thinking.

  • Practice metacognition. To activate meta-cognitive practices, which is thinking about one’s thinking, regularly step back from a problem so you can consider your thinking process. Get curious about all aspects of the situation, continually reflecting upon how you are approaching the problem. Ask: How else might I think about this?

  • Consider alternatives. Make it a habit of considering other possibilities by frequently asking: What else might this be? Do not be hesitant to consult with others when time allows. Sometimes a fresh set of eyes or ears can detect something that you don’t.

  • Accept that errors occur and learn from them. One way that people of all ages learn is through a process of trial and error.

  • Check your ego. Allow yourself to doubt yourself every once in a while. You may not realize it, but any decision you make could be biased, so take these cognitive errors, take the opportunity to learn and grow rather than evidence of your competency, worth or status. 

And, well, if you made it to this point, you proved me wrong.. maybe not all humans are lazy. With that being said, watch out for the similarity heuristic!

Similarity Heuristic: News
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