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Brain Storming and Market Sizing

brainstorming questions Market sizing mckinsey style
New answer on Dec 31, 2021
5 Answers
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Anonymous A asked on Feb 03, 2020

Hi everyone, recently I have done a case called "organ donation" (McKinsey Style).

I have several questions to seek your advice:

1. For McKinsey style cases, would the interviewer usually ask you to do a case structuring, just like candidate led case? If the interviewer directly starts from the first question, is it okay to ask for time to think about case structure and share with the interviewer?

2. For McKisney style cases, is a hypothesis required in the beginning?

3. One question of the case is to ask the key factors that impact organ donation rate. Should I treat it as a brainstorming question (where I could provide more quantitative ideas), or a market sizing question (where I need to list down a math function)?

4.Following the 3rd question, suppose it is a brain storming session, is it okay to mention qualitative factors that are hard to quantify (such as religious belief)? Or I should only mention factors that could be quantified and listed as a math function?

Thanks a lot!

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replied on Feb 04, 2020
McKinsey / Accenture Alum / Got all BIG3 offers / Harvard Business School


First of all - McKinsey has both Interviewer and Candidate led cases. Please be prepared for both. Candidate led cases are even harder.

1) Yes. Absolutely, you should take time to make a structure

2) I will add a post re the hypothesis below. Short answer - there is no Hypothesis requirement at McKinsey

3) It's a brainstorming question and you should provide as many ideas as possible. I also recommend structuring your ideas into buckets.

4) Both quantitative and qualitative. Think as broad as possible

Now, on the hypothesis:

First of all - it's not mandatory. I would say - use the hypothesis if you are really good at solving the cases. If not - use the basic approach

There are two ways to use the hypothesis:

First - presenting a structure using the hypothesis. For example, if you are having a PE (private equity) case, you should do the following:

1) Make classic structure (market, company, competitors, feasibility of exit)

2) Make subpoints (e.g. in market: size, growth rates, profitability, segmentation, etc)

3) Present your 1st level Hypothesis:

  • - "In order to understand whether we should invest in Company A, I would like to check that the Market is Attractive, the Company is Attractive, the competition is favorable and we have good opportunities for of exit"

4) Present the main 2nd level Hypothesis:

  • "In the market, I would like to make sure that the market is big enough and growing;
  • In the company I would like to find additional opportunities for growth;
  • In competition I would like to check that the market is fragmented enough;
  • Finally, I would like to check if we have potential buyers and can achieve desired exit multiples"

Another way to use hypothesis is using the hypothesis to prioritize your analysis:

1) Make a structure: "Problem in sales may be related to Sales Motivation, Sales Strategy, Sales Coverage, and Sales Process:

2) Prioritize a part of the structure based on your knowledge / common sense / available data: "Taking into account that motivation is the core problem of the sales organization, I would like to prioritize this part of the analysis"

Good luck!

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Content Creator
replied on Dec 31, 2021
#1 BCG coach | MBB | Tier 2 | Digital, Tech, Platinion | 100% personal success rate (8/8) | 95% candidate success rate

Hi there,

Providing some market sizing thinking for anyone revisiting this Q&A:

Remember that there's rarely a "best" answer with market sizing. What's important is that you break down the problem the way it makes sense to you. Importantly, break it down so that the assumptions you make are the ones you're most comfortable in.

For example, do you know all the major brands? Great go with that. Do you understand all the segments of that country's population (either age or wealth or job breakdown)? Go with that. Do you know the total market size of the tourism (or hotel) industry? Then break it down that way.

Some tips:

  1. Just like in a case, make sure you understand the question - what are you really being asked to calculate
  2. Decide whether a top-down or bottom-up approach is best
  3. Figure out what you know you know, and what you know you don't know, but could estimate
    1. This helps you determine how to split out buckets
  4. Stay flexible - you can start with a "high-level" market sizing, but gauge your interviewers reaction....if it looks like they want you to do more...then go along level deeper in terms of your splits
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Content Creator
replied on Feb 08, 2020
McKinsey | NASA | top 10 FT MBA professor for consulting interviews | 6+ years of coaching

1. Yes, you should ask for it.
2. I recommend to do it after some clarifying questions in order to better understand the context.
3&4. Market sizing approach with a qualitative discussion about each factor of the formula.

Hope it helps,

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Content Creator
replied on Feb 05, 2020
BCG |NASA | SDA Bocconi & Cattolica partner | GMAT expert 780/800 score | 200+ students coached


Here there are my answers to your questions:

  1. Usually the interviewer will let you to structure your solution and then he will start asking questions. If this does not happen, don't lose time doing a structure that is not correlated to your answer because your interviewer will get only annoyed. The first golden rule is to be effective and goal driven.
  2. No, there isn't any special instruction about that. You can use your standard approach that can can either have an initial hypothesis statement or not.
  3. When the interviewer asks for "key factors", he usually wants you to do a brainstorming. Try to be always structured and start from the most relevant but then you can and you have to be creative. Then, if he asks you to calculate the numbers, pick the most relevant and "quantitative" factors.
  4. Absolutely yes, and you can even include it in the math function as an additional factor


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Content Creator
replied on Feb 05, 2020
McKinsey | Awarded professor at Master in Management @ IE | MBA at MIT |+180 students coached | Integrated FIT Guide aut


1. Don´t get crazy about what´s called "McK Style". MBB interviews are indeed very very similar to each other. Normally, they will do the classical lay out of:

  1. Presenting the case and leaving you some time for questions
  2. Issue tree
  3. Follow up questions on it, including brain stormings or numerical questions

2. Not really, you will arrive to the conclusion precisely by solving the case.

3. Since they are asking about "factors", I would go with the brainstorming. In a later stage you can also crunch some numbers to back up your initial ideas, if asked.

4. Absolutely!

Hope it helps!



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