How to be MECE?

MECE is a buzz word in consulting and is often used in preparation for case interviews.But what is behind the acronym? This article takes a closer look at the MECE principle, its meaning and examples of its use. MECE is a Best Practice Method for Structuring Case InterviewsMECE is a way of segmenting information into sub-elements that are Mutually Exclusive and Collectively Exhaustive. In other words, elements should “exclude” each other, i.e. be distinct, and should “exhaust” the relevant field, i.e. contain everything that belongs to it.The MECE framework as a method should be used when you craft an issue tree for your case structure. Doing so will help you avoid dependencies between different branches of the tree, and thus sub-problems can be properly isolated.Mutually Exclusive (ME): aims at reducing complexity by avoiding overlaps. You need to make sure that the possible solutions or groups are not accidentally considered twice. Proving exclusiveness forces you to carefully look at each option, consequently leading you to a much deeper understanding of the issue.Collectively Exhaustive (CE): aims at ensuring a comprehensive collection without leaving alternatives. Exhaustive means that all possible options have been considered. The trick is to divide a problem into categories with a finite number of general groups. For example, if you need to make “means of transportation” MECE, don't start just collecting “per foot, train, plane, bicycle, etc.” Try to find categories, because this practice will prevent you from forgetting important options: wheels vs. no wheels OR air vs. water vs. land. Difference between MECE and non-MECE – A Simple ExampleA simple example for a MECE breakdown is dividing the population into subsets of age:A group of people below 50 years and another group of 50 years and above is MECE. No person can be in both groups - mutually exclusive - but every person is in either one of them – collectively exhaustiveA group of people below 50 years and another group with people from 40 to 70 years is not MECE, as people from 40 to 50 years belong to both groups - they are not mutually exclusive – and people above 70 are in neither one of the groups – they are not collectively exhaustive. A very common mistake made in this context is to differentiate between people below the age of 50 and people above the age of 50, but this does not include people who are exactly 50 years old.The MECE methodology is very famously used at McKinsey and other top consulting firms all over. Interviewers will especially evaluate whether you are able to structure information in a MECE format – a skill you will not only need in your case interview, but also in everyday life as a consultant. Many well-known frameworks, such as the Cost-Benefit-Analysis, 4Cs, or Porter’s Five Forces are designed with the MECE principle in mind. Use the MECE Principle in Profitability Cases to Split Costs in an Issue TreeThe MECE principle is not only applied for structuring information, but also helpful for simplifying calculations. Questions that require calculations are common in interviews as they are a good way to test your logical thinking and basic math skills. For example, it may be necessary to analyze the cost structure of a company in order to identify the root cause of a profitability problem. A good approach to tackle this task would be to break down the total costs into its single (MECE) components as you can see below:If as a next step you want to calculate the total costs, it is easiest to start at the bottom of your issue tree and carry out the first calculation. Take the result of that calculation and work your way up the tree until you have got the final costs. It is much easier to break down your problem like that than trying to do everything at once. Each calculation can be done in your head (if you need some practice, check out our Mental Math Tool) and is not overly complicated. When you have followed the MECE principle and made some valid assumptions for the actual numbers, your result will most likely be quite accurate (if you have made a sanity check and feel like it is not, it is also easy to look for the mistake by going through the structure of your tree again).👉 Take a look at our case “Startup vs. Consulting” and practice how to break down costs in a MECE way.

The Issue Tree is a valuable tool for analyzing the causes of issues during a case interview. When faced with a complex issue, the Issue Tree helps you break it down into its components. By focusing on the most urgent aspects and employing a hypothesis-driven approach, you can progress more quickly—a skill highly valued in consulting. 🚀🔎 In this article, you'll learn how to effectively use the Issue Tree, understand the differences between problem-based and solution-based trees, and how to leverage this technique to excel in your case interviews. Problem-Based Tree vs. Solution-Based TreeIn case interviews, two main types of Issue Trees are utilized:Problem-Based Tree: This helps you identify and understand the root causes of the issue and why it occurred in the first place.Solution-Based Tree: This is used to develop recommendations and clarify how the issue can be resolved.Ensure that the issues are MECE (mutually exclusive, collectively exhaustive). Otherwise, it will be challenging to address each area effectively. Use a hypothesis-driven approach to tackle the most significant issues first (see Pareto Principle).In consulting, the preferred approach is "answer-first" or "results-first." This involves starting with the main solution or conclusion and then working out the rationale. This is closely related to the Pyramid Principle.💡 Prep Tip: Practice these and other essential frameworks with our drills! Issue Tree as a Foundation for Consulting ProjectsAt the start of a new project, your team typically creates an Issue Tree. Once you agree on all relevant sub-issues, you gain an overview and focus on the key questions based on your hypotheses (answer-first style). Since all branches of the Issue Tree are MECE, the project manager can efficiently distribute the workload across the team. Each branch leads to a separate workflow that can be worked on independently, avoiding unnecessary interfaces that could cause inefficiencies. This explains why a small consulting team can achieve a lot in a short time.Once the causes of an issue are identified, the team uses a solution-based tree to determine how the issue can be resolved. Example of an Issue Tree in a Case InterviewImagine you need to calculate how many people can stand simultaneously on an airport runway during a case interview.Step 1: Problem Analysis with the Top-Down ApproachIn the top-down approach, you start by structuring the main problem or the case question and systematically break it down into its individual components. The goal is to identify all relevant areas or factors that influence the problem.First, you consider the overarching components (e.g., the total area of the runway) and then break these down into more specific details (e.g., the width and length of the runway).Step 2: Solution Development with the Bottom-Up ApproachIn the bottom-up approach, you focus on concrete numbers and data at the most detailed level of the problem and work your way up. You estimate necessary values, such as the width and length of the runway, and use these in your calculations to solve the main problem.As you can see, the top-down approach allows you to systematically break down the main problem into its components and identify all relevant influencing factors. The bottom-up approach then helps to develop a well-founded solution to the main problem by analyzing specific numbers and data.💡 In our case library, you'll find over 200 cases on various topics that will help you practice creating an Issue Tree! Check them out. Key Takeaways on Issue Trees in Case InterviewsThe Issue Tree is a central tool for structuring your case and developing hypotheses.Differentiate between problem-based and solution-based Issue Trees.Use hypotheses to quickly identify the root causes of the issue.Ensure Issue Trees are MECE to avoid inefficient dependencies between branches.👉 Prep Tip: Practice your cases with peers and arrange meet-ups on our meeting board.