MECE Principle in Case Interviews

M.E.C.E (pronounced "me see") is principle often used in management consulting circles to describe a way of organizing information that is "Mutually Exclusive, Collectively Exhaustive".

When creating categories of information such as "What are this company's options for growth?", "How can we cut costs?" or "How can we increase units sold?", the MECE ways means all the categories are defined in such a way that there is no overlap (mutually exclusive) and that all the categories added together covers all possible options (collectively exhaustive).

Here's an example of a grouping structure that is NOT MECE.

Grouping customers by their hobbies. (It's not MECE because a single individual customer may appear under more than one hobby category).

An alternative that is MECE is to group customers by age group. This is MECE because no one individual can appear in more than one category (hence it is mutually exclusive) and the age groupings taken as a whole cover the entire population (so they are collective exhaustive).

The reason MECE is popular in consulting is because it's less confusing to communicate to clients.

The MECE principle can be applied to groups of related items (like customers of different age brackets). MECE can also be applied to explain a particular mechanism.

For example, [ Profits = Revenues - Costs ] is a MECE framework. It very simply communicates that to increase profits one of two things must happen. Revenues must increase or costs must decrease.

You can break down Revenues into its own MECE components with the formula [ Revenues = Price x Units Sold ]. This too is simple enough for most people to understand. By using this approach to break down a financial metric into intuitively easy to grasp components that are also MECE makes it easy to see what operating "levers" you can use to influence the financial metrics you're trying to improve.

The definitive book on this subject is the Pyramid Principle by Barbara Minto. It's a book that describes an approach to communicating complex ideas in easy to understand ways. It is based on the MECE Principles and was a book often referred to and used while I was at McKinsey. (Note it's a pricey book at $150/copy)

While I never actually read the book, it was used by everyone every single day that I ended up picking up the principle through my colleagues and later read summary materials used during internal firm trainings.