Market sizing questions

case question Interviewer Market sizing
Neue Antwort am 22. Dez. 2022
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Emma fragte am 17. Nov. 2022

Sometimes, after finishing a market sizing question, the interviewer asks us what assumptions we think could change in our approach or what assumptions could vary.

I am not sure what to answer to these questions. Should we just pick one assumption from our answer and say that it could be different?

I don't know if my answer if clear, but if you could also give me an example that would be great!

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antwortete am 19. Nov. 2022
Bain | EY-Parthenon | Roland Berger | FIT | Market Sizing | Former Head Recruiter

When you finish your market sizing you should:

1. Check if the result makes sense. More important than not making calculation mistakes is the ability to sense if a number “feels” right or wrong. It can “feel” wrong either because you did mistakes in your calculations or because or had wrong assumptions (or an overall bad approach, but let's hope that is not the case).

2. If the result doesn't make sense (or the interviewer asks to review assumptions), you should know what are the “weakest links" in your assumptions. Those with the highest impact or least certainty/confidence. 

For example, if I was estimating the number of baby diapers, I would probably feel confident on the population size, % of babies, but probably not as much on the number of diapers used per day. That would be the one assumption I would review more carefully.

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antwortete am 17. Nov. 2022
BCG I Strategy& I 12+ years of professional experience


There are two parts to this. 1) assumptions that could vary - As you put together an algorithm/equation for your market sizing calculations and start making assumptions for each dimension, the ones where you have absolutely no basis or reasons to back your reasoning behind the assumptions are the ones where you would go back and potentially question them. for e.g - coffee drinkers in a country - you split the population into different age groups and take an average percentage of coffee drinkers across each - this percentage is the one which could potentially vary 

2) different assumptions for your approach - this is where interviewer probably expects to lay down a different algorithm for your market sizing calculation using different set of assumptions . For the same example above - you could split the population by income or even take a supply side approach to answer the question

i hope it helps. Happy to have an offline discussion to clarify further if needed. Good luck ! 

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antwortete am 18. Nov. 2022
Ex-McKinsey, former recruiting team member

I second everything everyone said! The other piece I would point out is what biases/your POV could be present that could change the answer. For example, one market sizing question I was given was “how many college students are in the USA”. Now, there were a LOT of things I don't know: what % of 18 year olds enroll in college? What % of USA college students are international students? When the interviewer asked me what assumptions could be wrong, I said “I assumed x% of 18-22 year olds are in college, but this of course varies by state, city, socioeconomic status, etc. So while I guessed x% based on my experience/research, this could be a lot lower/higher for the country as a whole.”

I think as consulting firms are looking for people who are well rounded and diverse, take a look at your assumptions and say “did I estimate this because this is MY experience and could be different for others?" 

This strategy of course isn't used for every market sizing question (no need to call out biases for number of golf balls that fit on an airplane) but as consulting firms look to be more inclusive, being introspective about assumptions can be good strategy

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antwortete am 18. Nov. 2022
Ex-BCG Principal | 8+ years consulting experience in SEA | BCG top interviewer with ~5 years of interviewing experience

In addition to what's been mentioned by other coaches, it could also be that your approach is not wrong per se but perhaps not complete.

This means that you might have missed out 1 or 2 more additional drivers and/or further segmentations of a variable that has a material impact on the answer.

i.e. It could be that the sizing only applies to one gender of the population (50% of total population), but you had assumed total population. 

From a practical POV, when asked this question by the interviewer:

  1. Identify what are the top drivers that have the greatest impact/sensitivity on the answer (like what Emily mentioned)
  2. Ask yourself a few potential questions
    • What are the drivers behind this assumption?
    • Is the basis and logic of my current assumption really justifiable/reasonable?
    • Is there another further breakdown or segmentation of this variable/assumption that would make a meaningful difference if changed
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Content Creator
antwortete am 18. Nov. 2022
MBB | 100% personal interview success rate (8/8) and 95% candidate success rate | Personalized interview prep

Hi Emma,

This might be happening if you're not sense-checking your end number (always make sure to verbalize the sense-check of your final number!).

When they ask about your past assumptions, it might be that nothing is wrong and they're just testing your thinking OR you've made a poor assumption.

Remember that we are estimating NOT guessing/assuming. 

When they ask you to check assumptions, take a look at which ones are more guesses and/or which ones might be unrealistic.

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Content Creator
antwortete am 17. Nov. 2022
Top rated McKinsey Case & PEI coach/Multiple real offers/McKinsey EM in New York /6 years McKinsey recruiting experience

The entire market estimation problem is built on assumptions. When asked what assumption would you change its good to see what assumptions have the biggest impact on your answer and communicate that to the interviewer, offering to alter it as needed.

You could also highlight that there are multiple approaches to market sizing and you can suggest alternative approaches (top down vs bottom up for example)

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antwortete am 22. Dez. 2022
50% off multi-session booking | FREE intro call | Moved from econ consulting to BCG | 2022 MBB interview experience

My strategy would be to flex the assumption which is the most “behavioural” one, such as the take-up rate. This allows for a much better discussion with your interviewer and is a much more commercially-savvy way of doing so (e.g. that is what normally happens on cases).

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Content Creator
antwortete am 17. Nov. 2022
Ex McKinsey EM & interviewer (5 yrs) USA & UK| Coached / interviewed 200 +|Free 15 min intro| Stanford MBA|Non-trad

As all of a market sizing is based on assumptions they’re probably testing your ability to know which assumptions have the greatest impact on the overall answer. I’d choose the three biggest ones and tell the interviewer what the impact on the answer would be by making them bigger or smaller

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Bain | EY-Parthenon | Roland Berger | FIT | Market Sizing | Former Head Recruiter
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