A Tale of Two Trees

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Those of you who follow this blog – despite the anaemic posting frequency – you would have notice that I still haven’t finished explaining the totality of the Case Interview Process Model©. There is actually a good reason for this.

Believe it or not, I was actually working on the last part of the explanation those last few days when I had the chance to actually coach one of my friend about consulting case interviews, using the very model I proudly introduced a year ago.
Well, to my great dismay, two problems appeared during the session:

1. The model flow was not optimal; and
2. The model was incomplete!

While issue #1 is really all about the gymnastics of going up and down the issue tree (if you don’t know what this barbaric term means, please have a look here), issue #2 is far more serious but also provides far more insight.
What the model was lacking all along is the effective separation of the analysis of a case interview into 2 parts, one after the other:

1. A diagnostic analysis
2. A solution analysis

All credit here must be given to Arnaud from Powerful Problem Solving who literally enlightened me with his method. Arnaud rightfully points out that in problem solving, the analytical process must first diagnose the problem using what he calls a Why tree, then solve the problem using a How tree.
This is vey powerful and elegant at the same time. And this is an advice that I haven’t heard from any consulting guru so far (not even my estimated Victor Cheng).
Arnaud is so right in his approach. The most complete case interview will always ask you to find the root cause of the problem at hand (hint: you must first be able to define the problem) and propose a solution to the problem.
Because we are highly structured folks, we then use issue trees to tackle both issues: the diagnostic and solution.
Let’s consider a very standard problem thrown by case interviewers:

Company X has seen profitability declined over the last 2 years. They called you for help.

This is indeed very case-like (and very dull too). The point is, even with this simple problem, you will greatly gain by separating your analysis into two, and conveying to the interviewer that you do so.
You would then start the analysis by finding the key driver of the problem, probably using the uber-used profitability tree. Let’s imagine that the cause of Company X’s falling profits is that there volume of sales has been declining.

Now that we have the diagnostic, we must solve the problem to complete the case. So this is where imagination and structure are really needed. In our example, we could think of the following solutions.

By the time we have identified the possible solutions to the problem at hand, we are ready to close the case.
Important: remember that both trees must follow an hypothesis-driven style of analysis. Each branch of the tree must be proved of disproved by the acquisition of information, either from the interviewer directly, your best estimate or the charts provided.
This last paragraph is supremely important and is the substance of the case resolution (we will talk in length about this in future posts).
So you now have an even clearer picture about the dynamic of the case interview analysis, with the breakdown between WHY and HOW trees. Naturally, I will reflect this in a new version of the Case Interview Process Model (along with flow improvements) so stay tuned!