MECE in Case Interview

MECE is one of the most important principles in management consulting about organizing and breaking down anything from problems, information, approach, to workstreams.

Consultants work, speak, write, eat, and sleep with this concept. If you want to be a consultant someday, this concept becomes a must-know and must-show in Case Interviews.

What is MECE?

MECE stands for “Mutually Exclusive and Collectively Exhaustive”.

That sounds like a buzz word, but if you watched our Case Interview 101 video, you would know that it really means just two things. Small parts cannot overlap and the sum of those small parts needs to be equal to the big item. If you haven’t watched that video, I strongly encourage you to do so. Though just to briefly explain the concept of MECE, it is important to see where MECE stands in the big picture of a case interview.

In this video I will explain these two insights in greater detail and I will also introduce more insights which every consulting candidate should know. After that we will look at some examples of non-MECE in various settings and also a practice problem in order to be more MECE in case interviews.

So, what makes an approach or a break down MECE?

There are 4 characteristics of it. Let’s talk about each one.

No.1: The “ME” part – Small pieces cannot overlap with each other

For example, a non-MECE way to break down the customer groups of In&Out restaurant is:

  1. Walk-in customers
  2. Male customers

This is non-MECE because there is an overlap. Some walk-in customers are male and some male customers can be walking in.

No.2: The “CE” part – The sum of small parts needs to be equal to the big group.

Let’s say we fix the above example a little bit. Now the breakdown of In&Out restaurant is:

  1. Walk-in customers
  2. Online customers

Even though the overlapping is removed, this is not yet MECE as the sum of the 2 groups does not represent the whole customer group. In&Out also offers drive-through service and these customers don’t fall into either of the two groups listed above.

Technically, the term MECE only means those two things. However, the implication goes beyond that. Let’s talk about it.

No.3: Small elements need to parallel each other, or in other words, be in the same class

For example, a non-MECE way to break down the customer groups of In&Out restaurant is:

  1. Las Vegas area
  2. Salt Lake City area
  3. California

While there’s no overlap and the sum of these three groups is approximately equal to the big group but this is not MECE in the sense that these small groups are not on the same level. Doesn’t matter if we go for states or for metropolitan areas but we need to be consistent.

No.4: Stick to the magical “three”

What if a candidate at this point proposes a method that meets all of the above as follows:

In&Out customers can be broken down in the following groups:

  • 0 -10 years old
  • 11 – 20 years old
  • 21 – 30 years old
  • 31 – 40 years old
  • 41 – 50 years old
  • 51 – 60 years old
  • 61 – above

There’s no overlapping, the sum really is equal to the total group, and all parts are parallel. However, this is not considered MECE in the sense that there are too many parts. Normally the human mind cannot comprehend more than 4 items.

The management consulting industry has been using this principle for years. We call it the magical “three”. In which the optimal number of bullets, ideas, and elements is always 3. Sometimes, we may use 2 or 4, but over 5 is too many.

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