Heuristics vs. Biases: The Difference


Do you think there are more words that begin with the letter r or do you think there are more words that have the letter r as their third letter (i.e: car)?

If you’re like the rest of us, you decided there are more words that begin with the letter r than words that have r as their third letter. Why? Because more r starting words came to mind when you searched your mental database than r middle words. This is because we usually search for words in our memory by their first letter, not by their third — thus words starting with r were more available to your memory than words with r as their third letter.

You just used a mental shortcut known as the availability heuristic to answer that question.

Kahneman & Tversky first wrote about the availability heuristic in their 1974 paper entitled Judgment under Uncertainty: Heuristics and Biases. In the paper, they provide the same example I gave at the beginning of this piece and explain the answer to the behavior in this way: “Because it is much easier to search for words by their first letter than by their third letter, most people judge words that begin with a certain consonant to be more numerous than words in which that same consonant appears in the third position”

Basically, the availability heuristic says that people tend to judge the accuracy, occurrence, or impact of something based on how easily they can find the relevant information about that topic in their mind. It’s the reason people think that shark attacks are more common than they really are and the reason that people tend to overestimate the rate of homicides and underestimate the rate of suicides — in 2017, for example, there were more than twice as many suicides (47,173) in the United States as there were homicides (19,510).¹

Photo by Yuval Levy on Unsplash

I am really interested in heuristics as a topic, and I wrote an article called How Judgements Happen that goes into detail on how heuristics are formed. To keep it short here, a heuristic is a mental shortcut that we use to make quick intuitive decisions about daily activities. Many people refer to heuristics as mental rules of thumb and most are in agreement that heuristics don’t always help us make the most optimal decision, but 9 times out of 10 the use of a heuristic will save us from making really risky or catastrophic choices.

In recent years, heuristics have gained a lot of attention partly due to the brilliant work of scholars Daniel Kahneman and Amos Tversky, and partly due to the innovative cross-disciplinary work of other scholars like Richard Thaler, (economics) Cass Sunstein (public policy) and Rory Sutherland (marketing).

Along the same line of research, cognitive biases have gained a great deal of attention- especially in the consulting, media, and business coaching circles. These types of thought-models are similar to the thought-models of heuristics in that they are used by people to make short-cut judgments about situations, but biases are different from heuristics in some fundamental way.

The problem is, this fundamental difference seems to be elusive.

The founding fathers of this entire thought-proccess believe that biases are the result of judgmental heuristics.

While I may not be able to specify the definitive difference between a heuristic and a bias, I can confirm that they are not the same thing. It’s important that we understand that these two words can’t just be used interchangeability.

Beyond that confirmation, I can’t really establish anything as fact so this is my well researched and honest attempt to sort through the two mental-shortcut models and come up with a plausible separation between them.

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Side Note: In case you were wondering what authority I have to confirm that heuristics and biases are different things, in that same paper by Kahneman and Tversky I cited earlier, it is written: “This article has been concerned with cognitive biases that stem from the reliance on judgmental heuristics.”

So, it is clear that the founding fathers of this entire thought-proccess believe that cognitive biases stem judgemental heuristics and thus are biases are the result of heuristics. From my exploration of the subject, I am inclined to agree.

Types of Heuristics

Here is a brief overview of the 4 judgemental heuristics that Kahneman and Tversky discovered. These are the most widely accepted heuristics, meaning pretty much everyone is in agreement that these are judgemental heuristics.

  • Availability Heuristic: the tendency to overestimate the likelihood of events with greater “availability” in memory.
  • Affect Heuristic: the reliance on a “good” or “bad” feeling in making a decision. Basically, trusting your intuition to make quick judgment calls.
  • Anchoring and Adjusting Heuristic: when estimating uncertain quantities, people tend to start from a given number (the anchor) and adjust either higher or lower depending on what seems reasonable. Kahneman notes in Thinking Fast and Slow that “The adjustment typically ends prematurely, because people stop when they are no longer certain that they should move farther” meaning, people often overpay as a result of anchoring.
  • Representative Heuristic: the degree to which A resembles B influences the degree to which people believe A originates from B. An example of this is the best way to make this clear so: if asked to choose whether a librarian (A) had a side-hustle of either an animal shelter volunteer (B) or an r&b singer (C), most people would guess that the librarian worked as a volunteer because that seems more like a librarian hobby. A resembles B, and influences the degree to which people believe they are related.
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Types of Biases:

There are literally hundreds of these cognitive biases. Some of these were discovered and cited by Kahneman and Tversky (hindsight bias, for example) but many of them have been identified by other scholars. To keep it simple, I have just listed the top 5 most widely known and well-researched ones.

  • Confirmation Bias: seeking out information that confirms the beliefs you already have. This can take many forms including searching online, talking only to people who share your view or watching certain TV channels.
  • Overconfidence Bias: believe that they have better ability than they do.
  • Hindsight Bias: the belief that past events were predictable at the times that those events took place. This is almost never true because it’s unlikely that there was enough accurate information available at that time.
  • IKEA Effect: people value things that they build as way more highly than any other objective person would value that same thing.
  • Novelty Bias: the tendency to prefer something just because it is new.

Understandings of Heuristics & Biases

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Heuristics are generally accurate representations of reality.

From what I understand, heuristics are:

  • often oversimplified evaluations of situations
  • based on experience and/ or learned lessons from others

Biases are generally distorted misrepresentations of reality.

From what I understand, biases are:

  • not a cognitive evaluation of a situation but rather a belief or an influence
  • based on preference and/ or desired public perception

This is just a hunch I have but I believe that another fundamental difference between the two is the action/ feedback/ learn repetition loop. What I mean is, if you repeat a behavior several times and find contradictory information you would adjust a heuristic but you are far less likely to edit a bias.

For example, once you learn the stats about how rare shark attacks really are (there are less than 100 attacks globally every year) you adjust your mental model of shark attack probabilities and go to the beach without fear. That’s an example of adjusting your availability heuristic- it’s pretty easy to do.

Now compare that to adjusting a bias. Even if you are shown evidence that proves the ingredients are the same in one brand of coffee as compared to another brand of coffee, you’re still likely to prefer one over the other. The two brands can be literally exactly the same, but biases are just hard to change.

Photo by Sara Dubler on Unsplash

Here is a concrete example of how I think about sorting the difference between heuristics and biases: for me, the difference between the two is akin to the difference between animals and dogs. All dogs are animals but not all animals are dogs.

In thinking about why it’s important to distinguish between heuristics and biases, I tend to gravitate toward the concept of logical reasoning.

Not everyone wants to figure out how the world works, some people just live in it- and that’s fine- but personally, I find it really important to understand the properties of reasoning because it allows me to gain insight into the workings of human behavior and potentially to make sense of the world.


Written by


Unapologetically, endlessly, curious. @RoamyWrites on Twitter

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