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Could you please share any framework to assess market sizing questions? Many thanks

Anonymous A asked on Aug 09, 2019 - 2 answers
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Vlad replied on Aug 09, 2019
McKinsey / Accenture / Got all BIG3 offers / More than 300 real MBB cases / Harvard Business School
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1) First of all, there are two ways to calculate market size:

  • From supply side (e.g. vending machines spots)
  • From demand side (e.g. vending products consumption)

2) There are 2 ways to structure market sizing:

  • Formula - basically a math formula to come up with a solution. The problem with the formula is that it is easy to forget something or get lost.
  • Tree - same as with regular cases you build a tree. A very simple example: you need to calculate the number of dogs on manhattan. A number of dogs = share of households having a dog * # of households. # of households = population / average household size. In the end, you'll have a pyramid where you have to fill the numbers on the base of the pyramid. This approach is much easier and help you track all the numbers

3) You should learn the key market sizing techniques:

  • Making assumptions based on personal experiences (Use the example of your house where out of 100 apt-s 10 have dogs)
  • Adjusting numbers (NY is a busy city thus fewer people have dogs)
  • Sanity check - try to apply your calculations to real environment
  • etc.

4) You should learn the key tools:

  • Using age even age split (suppose life expectancy is 80 years. Assuming even age split we have 4 mln people in US of each age group)
  • Using 80/20 split (suppose 20% people earn 80% wealth and the average salary is xx...)
  • Using approximations (Length of NY-SF flight and plane speed to calculate US length)
  • etc.

5) Learn key numbers: populations, gas price, gas consumption, Boeing speed and nmber of seats, average salary, # of gates in the airport, GDP growth rate, inflation, etc.

6) Practice 10-15 cases and you'll be fine

Good Luck!

replied on Aug 09, 2019
McKinsey & Co. | Vice President of IESE MBA Consulting Club | Experienced coach
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There is no a “one-fit-all” market sizing framework, because they mostly depend on the type of question and the inputs coming from the interviewer.

However here a useful structure to be applied for this type of questions:

1. Ask clarifying questions

The first thing you should do is ask a few clarification questions to make sure that you know exactly what number your interviewer wants you to calculate.

In addition, they are also a great way to buy yourself some time. While your conscious brain asks these questions, your sub-conscious brain can start working on the related calculations and reasoning.

2. Map out your calculations

Once you know exactly what number you want to calculate you need to map the calculation steps to get to that number.

A good approach is to start from the number you want to calculate and draw an issue tree from top to bottom as we have below. The advantage of that approach is that the issue tree will force you to be MECE (i.e. not forgetting anything and not overlapping things) and it will also give you a starting point.

You should validate your approach with your interviewer before starting to calculate numbers. This is important because it gives your interviewer a chance to rectify your course of action if they had another plan in mind.

Skipping this validation step is extremely risky because your interviewer might only realise half way through the case that you are approaching the problem in a different way to what they wanted you to.

3. Round numbers and calculate

Once you've agreed an approach it's time to start calculating. You will need various data points to get to your final estimate. In most cases your interviewer will ask you to make your own assumptions to get to the final number. But in some other cases they might share data with you. The best way to find out which situation you are in is to ask the interviewer which approach he/she prefers.

When making assumptions it is vital that you pick simple numbers. In addition, you should talk out loud when doing calculations so that your interviewer can follow your thought process. Your interviewer is interested in what's going on in your head - not the final result.

4. Check your results

Finally, most candidates stop talking at the end of step 3. They look up and expect their interviewer to tell them if they got to the right result or not. This is a mistake. The best candidates sense-check their results and try to spot their own mistake before telling their interviewer they are done.

Mental calculation errors happen frequently. If your interviewer spots a mistake in your calculations, you most likely won't get an offer. But if you spot your own mistake you still have a chance.

So check your own calculations and give a “so what” to the results.

Finally, before the interview it’s always useful to prepare a “cheat sheet” to memorize some common assumptions such as population and life expectancy as they will often come up in market sizing questions.

Here an example for US:

  • Population: ~325m
  • Households: ~100m
  • Person per household: ~3
  • Median household income: ~$60k
  • Life expectancy: ~80 years old

Hope this helps!

All the best!


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