MECE - Mutually Exclusive, Collectively Exhaustive

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This is my third post in a row on frameworks (two weeks ago I wrote about the lean framework and last week I posted on six sigma frameworks).

Why am I stuck on frameworks? It's about thinking. Having a framework to use in problem solve structures your thinking on how to solve that problem. It's as if you have a roadmap towards solving your issue - you just need to know about the different kinds of roadmaps to choose from.

And knowing these different frameworks helps with communication. Whether you are communicating up to your company's leadership or communicating with your team, being able to describe how the team should go about solving the problem increases your credibility as an "expert". Having this credibility from the onset makes your job in leading the team through whatever problem solving process you choose much easier.

This post is about a framework that isn't part of the six sigma or lean "body of knowledge." But I've categorized this post under lean six sigma because what we do in LSS is problem solve. Knowing about the MECE concept and putting it to practice will make you a more capable problem solver for your company or business.

What is MECE?

MECE (pronounced "me-see") stands for "mutually exclusive, collectively exhaustive." Let's break this down into it's two parts:

Mutually exclusive. T means all the things in the group/list either don't include each other or there's no overlap in any of the items in the group/list. Each idea or issue is distinct and different from each other.

The illustration to the left shows that both ideas are separate and distinct from each other. The two items don't share anything in common with each other. Contrast that to the illustration on the right where the two items overlap. This overlap in the ideas makes the set not not mutually exclusive.

Collectively exhaustive. Broken apart, this phrase means the whole group (collectively) includes every relevant aspect (exhaustive). In short, collectively exhaustive means that every aspect of the problem has been accounted for. In other words, have you and the team thought of everything?

This one is more challenging to illustrate. Missing ideas, gaps, and omissions lead to a problem description that is not collectively exhaustive.

Mutually exclusive, collectively exhaustive. Putting the two parts together means there are no overlapping issues and every aspect has been thought of. Additionally, MECE thinking requires that every aspect considered falls under one, and only one of the issues identified. If an aspect falls under multiple issues, then there is overlap the problem description that you have isn't MECE.

A simple example

A pair of dice is a simple example of MECE. With a single six-sided die, you can roll a 1, 2, 3, 4, 5, 6. With a pair of dice, you can roll anything between 2 and 12 on any one of 36 different combinations. If you were categorizing every possible roll under MECE, that illustration might look something like below:

With every possible total (2 through 12), every one of 36 different combinations is accounted for, and each combination is assigned to one and only one dice total. This is a MECE categorized problem set.

Of course, a real-world issue won't be as neat and buttoned up as this dice roll problem. The key output of MECE is a complete set of issues that are spereate and distinct from each other, and together completely describe the problem that you are solving.

How is it applicable in lean six sigma?

This blog post gives three "simple" ways to think in MECE. The article talks about using a mathematics formula as one method and another is to use common lists as a starting point.

The tip that resonated with me is the idea of process mapping. Each process step, because they are separate and distinct from every other step, is mutually exclusive. Working through every step in the process is collectively exhaustive.

As process improvers, we know that any overlaps among steps and gaps or missing steps forces a discussion on defining exactly what the steps are resulting in a MECE-framed process description. If you have ever been satisfied with a process map thinking, "Yep, that describes the process completely," then you've successfully completed the MECE framework.

Why go through all the trouble?

Now, you're probably thinking, "Why go through all the trouble of first learning about MECE and then using it?"

Bottom line: It helps with thinking. Specifically, mastering the MECE framework will help you in accurately thinking about the problem, which leads to accurately describing the problem, which leads to effective problem solving.

The MECE framework is about grouping and categorizing the relevant issues of your problem. One of the necessary conditions for MECE is that there is no overlap in your issues. Overlap among the issues is a sign of muddled and confused thinking. The MECE structure helps to eliminate the overlap, which reduces muddling and confusion, which increases clarity of thought. With clarity of thought comes effective communication of the problem and, ultimately, effective problem solving.

There is one other benefit with MECE thinking. A general rule in MECE is to have no fewer than two and no more than five main issues for the problem. The ideal number is three because it's easy to remember. If you can keep between two and five, the information about the problem will be much more memorable. This is true for anyone you engage with, whether it's your project team or the CEO of your company.


As always, I like to close out my posts with resources to help you if you're interested in learning further. Below is a list of online sites and articles that I used in researching and learning about MECE.

  • If you like tacos, this post applies MECE to tacos.
  • A good article from ASQ. It takes the approach that DMAIC is the preferred problem solving approach and MECE is the preferred communication approach. (You'll need an ASQ login. It's free.)
  • Two blog posts related to McKinsey Consulting (post 1 and post 2). MECE was created by Barbara Minto, McKinsey's first female consultant.

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