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Market sizing: do I explain my approach first before talking about the number?

Hi there! I just started learning about case interview and I hope that somebody could help me out here! I am confused about how we do market sizing in the actual interview. I read that we should plan our approach first before jumping into the math, but when I go through the question with the interviewer, do I talk about my approach and the numbers separately? As in:

1) go through my approach from the beginning till the end first, and then repeat again with the numbers?

2) go through my approach and at the same time, mention the numbers as well?

Thankyou!

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Top answer
Deleted user
on Sep 27, 2021

Hello,

It would depend on the level of detail you are going for in the market sizing, and honestly either of the approaches you outlined could be effective in different situations. Generally I recommend going for #1 for the same reasons most of the other experts have mentioned here. It might feel a bit awkward at first, but generally makes for a smoother and more structured approach to the problem.

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Ian
Coach
on Sep 26, 2021
Top US BCG / MBB Coach - 5,000 sessions |Tech, Platinion, Big 4 | 9/9 personal interviews passed | 95% candidate success

Hi there,

While it does depend a bit on the exact structure of the market sizng (i.e. level of complexity), generally approach #1 is best.

Now, when going through the approach + numbers the key is that you are efficient in the way you articulate your structure/numbers. Try to list sections out together instead of saying each and every branch/number on its own.

Make sense?

Agrim
Coach
on Sep 26, 2021
Top Awarded Coach | BCG Dubai Project Leader | Master Casing in only 3 Hours | 10y in Consulting | Free Intro Call

Ideally the approach should be the following:

  • Explain the high-level conceptual approach without specific steps - in 1-2 statements
  • Then explain the approach in more detail with focus on the key drivers, levers, and some of the math concepts that would go into it
  • Then run through it again with the numbers in place - the numbers you can also calculate as you go rather than baking everything in the first 2 minutes of thinking time.
Udayan
Coach
on Sep 26, 2021
Top rated Case & PEI coach/Multiple real offers/McKinsey EM in New York /12 years recruiting experience

The simplest way I have found is to outline your approach first with the interviewer. Ask them if this approach works, once they are on board then go ahead and make the necessary calculations required. 

You do not have to keep walking them through the approach, once is more than sufficient.

Best,

Udayan

on Sep 27, 2021
#1 Coach for Sessions (4.500+) | 1.500+ 5-Star Reviews | Proven Success: ➡ interviewoffers.com | Ex BCG | 10Y+ Coaching

Hi there,

I agree with the other comments, option #1 is better.

In market sizing you do the same thing that you do in math in a case: you first present the theory, then add the numbers.

I think Agrim explained very well the approach to follow and that’s the approach I would suggest: 

  1. First level of the structure
  2. Details on subcomponents
  3. Add the numbers

Best,

Francesco

on Sep 26, 2021
Former McK interviewer, PhD who successfully transitioned from Academia, received offers from McK/BCG/Bain/LEK

Hello,

I can see your doubts as option 1 (in my opinion recommended) sounds a bit repetitive and thus artificial. However, it has benefits for the candidate as well as for the interviewer.

It separates conceptual thinking from estimating the numbers and performing math (and we always try to break down complex problems into series of simpler ones).

From the interviewer's point of view: when I see a problem with the approach, I can steer the candidate in the right direction before he/she becomes too entangled in the solving process.

Once we have an agreement as to the process, it's easier to troubleshoot in case the solution seems odd. Simply check the math and if that's correct then rethink assumptions.

I encourage you to practice in these 3 steps - should become more natural in a while.

Best,

Slawomir

Pedro
Coach
on Sep 26, 2021
Bain | EY-Parthenon | Senior Coach | Principal | Recruiting Team Leader

Yes, you should definitely follow aproach #1. 

This is always the rule in case interview: first explain how you think, then execute. 

Therefore, you first explain your approach to the interviewer and ensure that he understands it and agrees with it. Then you present your assumptions in a pragmatic way. Then you execute. 

If you start presenting the structure and the numbers together, I will be under the impression that you are jumping into execution without having actually thought through your whole struture, and that is a clear negative. It's not just worse communication, it also suggests a suboptimal way of thinking.

In my experience candidates do less mistakes, communication is more clear, and you actually get to the end result faster. And there are absolutely no doubts that you are strucutured in how you think and in how you solve problems.

on Sep 27, 2021
McKinsey | NASA | top 10 FT MBA professor for consulting interviews | 6+ years of coaching

Hi!

Definitely go for approach #1.

Good luck with your preparation.

Best,

Anto

on Sep 27, 2021
#1 Rated & Awarded McKinsey Coach | Top MBB Coach | Verifiable success rates

Definitely 1. Always always go through the approach. It’s helpful for multiple reasons.

First, you validate your thinking with the interviewer. It all resembles a real conversation you might have with the client. As long as they go with the reasoning, they will go with the answer.

Secondly, it helps you because you basically separate two cognitive tasks : structuring and calculating. If the structuring is fine, then you know you only have to worry about the numbers now