How to properly use issue trees to analyze problems and derive solutions?

Case Interview drivertrees issue tree Logic MBB McKinsey
Recent activity on May 06, 2019
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Anonymous A asked on May 06, 2019

Hello! I realize that I don't get anywhere when I try to use issue trees while solving cases. I struggle to understand what they are and how to properly utilize them in the process. I feel the typical case books don't explain this in an understandable way. Any help?

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Sidi
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replied on May 06, 2019
McKinsey Senior EM & BCG Consultant | Interviewer at McK & BCG for 7 years | Coached 300+ candidates secure MBB offers

Hi!

Issue trees are at the heart of the problem-solving approach. For case interviews in strategy consulting, two distict types are primarily important: diagnostic trees and solution trees.

Generally speaking, an issue tree is a graphical breakdown of your key question. Trees have four basic rules:

  • They consistently answer why or how questions (depending on your key question)
  • They progress from the key question to the analysis
  • Their branches are mutually exclusive and collectively exhaustive (MECE)
  • They use an insightful breakdown

Diagnostic trees are for diagnosing your key question

Diagnostic trees help you search for all the possible causes of a problem. They give you the "WHAT & WHY?".You list these in logical groups on the first column to the right of your key question, ensuring that your groupings are MECE. As you progress to the right, you drill further down in the details of each grouping.

Solution trees are for actively looking for ways to correct your problem

With solution trees, you look for all the potential solutions to your problem. They give you the "HOW?". As a general rule, you want to know the WHAT & WHY before you get to the HOW, so if you don’t know the root cause(s) of your problem, find these first by means of a diagnostic tree.

For broader context, issue trees progress further into details until elements are sufficiently explicit. Then come the hypotheses, analyses and data sources. Once you have tested which solutions are viable, you are ready to select one, for instance by using a decision matrix (impact vs. doability).

Example Diagnostic Tree for a household recycling issue:

problem-based issue tree

Example Solution Tree for a household recycling issue:

solution-based issue tree

Hope this helps!

Sidi

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Anonymous B replied on May 06, 2019

I face the same situation, I find it hard to solve the cases with issue trees however i have a feeling that if i can crack it, you won't need to memorize all the pre-defined solution structures which will save you a lot of mental energy

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Sidi on May 08, 2019

Exactly! Becoming a great problem solver requires the mastering of a METHOD, not learning facts or frameworks!

Sidi gave the best answer

Sidi

McKinsey Senior EM & BCG Consultant | Interviewer at McK & BCG for 7 years | Coached 300+ candidates secure MBB offers
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