Cognitive Biases — Unit Bias

The desire to complete a unit of a given task or item.

Michael Gearon
4 min readMay 26, 2019
Photo by Dan Gold on Unsplash

Unit bias is how people want to complete a task or fulfil an objective. An example could be if you were given a plate of food you feel obligated to finish it. That perception of completion is satisfying to people as you are finishing a task. It’s also worthwhile noting that sometimes the unit bias can be referred to as the completion bias, either way, they are both similar.

Why does this matter?

This bias is often looked at when it comes to diets and healthy eating as smaller the plate size the smaller the portion size which means we have less to consume and therefore less to complete the task.

However this bias can apply to all different scenarios from diets, to assembling furniture to form filling. Lets first look at an example of a study conducted by American researchers.

Portion sizes study

A study by Geier, Rozin, and Doros showed that participants would eat more candy when served with a large spoon than when they were served with a small spoon even though in both instances they had no limits to how many spoonfuls they could have.

Humans tend to see things as a single unit and don’t take into consideration to size of the unit. A 12 ounce soda is seen as one unit while a 24 ounce soda is seen as one unit even though it is twice as large as the 12 ounce soda.

This research shows that portion sizes should be kept small in order to encourage healthful eating.

When completion bias fails us

Eating too much because of our portion sizes can lead to obesity which is bad but there is further proof that the completion bias can lead to failure and making poor decisions.

Crisis planning

Gino and Staats's unpublished research looked at the completion bias of physicians in the emergency department (ED) of a busy hospital, where patients arrive without appointments.

“Using data from about 43,000 distinct patient encounters, we found that physicians exhibit a bias toward completing easy tasks when confronted with an increased workload due to an increase in the number of arriving patients,” wrote Gino.

In an ED setting, “easy tasks” refer to treating patients who are less sick.

From first appearances, this looks like a good plan, by treating the less sick there is fewer people and in-turn more completed. By focusing on these less-sick patients, a doctor is “more productive” because these patients don’t stay in the ED as long.

But, according to Gino and Staats, there are at least two problems with this approach:

  1. Patients with more severe conditions wait longer.
  2. With each “less sick” patient a doctor treats, that doctor slows down a little more — so there’s a chance she’ll get tired and less effective on the job before she begins seeing those patients with more severe conditions.

Why we put off big tasks

A study by Dr. John Bargh, an award-winning psychology researcher, showed that this is more likely to happen before we start working on a big project. In an attempt to simulate real, productive work, our brains tend to focus on small, mindless tasks.

So if you’ve ever thought the night before a big presentation was the best time to clean your place, respond to a friend’s text or binge on a TV series — or in general just procrastinate this is why.

In theory, it should be easy to fight the urge to tackle those smaller tasks. Just recognize which tasks are the most important, and prioritize them, already! But we all know that’s easier said than done. As the researchers, Francesa Gino and Bradley Staats, explain:

Your brain releases dopamine when you achieve goals. And since dopamine improves attention, memory, and motivation, even achieving a small goal can result in a positive feedback loop that makes you more motivated to work harder going forward.

The power of storytelling

When we start watching a film or read a book how many times have you got half way and thought this is terrible kept reading or watching anyway?

We are compelled to finish what we start otherwise we feel bad and curious to see how it ends. This is why when we build or market products that we must form them on a story. By providing a clear start, middle and end people will feel compelled to finish what’ve they started.

This could also work for your presentations, pitching to clients or whatever you're trying to accomplish, by providing this story format it will engage more people.


This is definitely one of less documented biases out there. However, the unit bias has its role a play into how people make decisions. The main takeaway from this is that if the research has shown people want to finish what they’ve started, make it as easy for them as possible to do this. If you’re interested in other cognitive biases then take a look at other ones I’ve written about.

Further reading



Michael Gearon

Senior Interaction Designer and Co-Author to Tiny CSS Projects