Struggling with Data Sufficiency

Case Interview Digital McKinsey
New answer on Jul 17, 2022
6 Answers
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Anonymous A asked on Jul 05, 2022

Hi all! Do you have any advice on how to determine whether you have sufficient data for a quantitative question? I sometimes seem to struggle with knowing what information I need to solve a math question correctly. Any tips would be great!

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Francesco
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replied on Jul 06, 2022
#1 Coach for Sessions (4.000+) | 1.400+ 5-Star Reviews | Proven Success (➡ InterviewOffers.com) | Ex BCG | 9Y+ Coaching

Hi there,

Q: Do you have any advice on how to determine whether you have sufficient data for a quantitative question? 

Good question. You should be able to understand that after presenting the formula you want to use.

The process to follow for the math part of the case is the following:

  1. Repeat the question – sometimes candidates do mistakes answering the wrong question
  2. Ask for time and explain how you would like to proceed, presenting the formula you want to follow
  3. Perform the math and present the interim steps to keep the interviewer aligned – don’t just say the final number
  4. Continue with the calculations until you find the final answer
  5. Propose next steps based on the results you found

So in step 2, you are presenting the approach you want to follow and the related formula. At that stage, you should be able to understand if you have sufficient data based on the formula itself.

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Example: you are calculating the breakeven point for volume and presented the formula as 

V = FC / (p-c)

You have the fixed costs (FC), you have the price (p) but you don’t have the variable cost (c). You can then ask the interviewer for information on that.

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Hope this helps,

Francesco

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Moritz
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replied on Jul 06, 2022
Unearth your spike & get the offer |ex-McKinsey | 120+ coachings & interviews @ McKinsey | ESADE MBA | Transition Expert

Hi there,

I'm not sure I understand your exact pain point, which may relate to data sufficiency and/or building fit for purpose formulas.

Let's test by looking at some scenarios:

  • Scenario 1: You have a fit for purpose formula laid out, given to you or derived by yourself based on context and objective → In this case you must ‘simply’ slot in the values you have and make estimations for those you don't have, ideally in agreement through conversation with the interviewer. Data insufficiency and the need for estimations and purposefully placed in the case.
  • Scenario 2: You have a number of variables but no formula to solve for a given objective → In the absence of a formula that is fit for purpose, you won't be able to tell as to whether your data set is sufficient/insufficient. In this case, you must be clear on the objective you're solving for and develop a formula with unknown variables, including units (e.g. x US$ revenue/unit sold).
  • Scenario 3: You neither have formula nor variables, which is more common than you think e.g. market sizing → In this case you must be clear on the objective you're solving for and develop a formula with variables that you can entirely estimate.

Reflect on the above and let us know which scenario we're talking about - this will allow us to guide you better.

Hope this helps. Best of luck!

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Clara
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replied on Jul 07, 2022
McKinsey | Awarded professor at Master in Management @ IE | MBA at MIT |+180 students coached | Integrated FIT Guide aut

Hello!

First, you don´t need to know right from the start whether you have everthing or not, you can finds this out as you progress in the problem. 

What always helps is try to break down the calculations in all the little pieces at the beginning, and then see what you have and can get, and what is missing. 

Hope it helps!

Cheers, 

Clara

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Ian
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replied on Jul 06, 2022
MBB | 100% personal interview success rate (8/8) and 95% candidate success rate | Personalized interview prep

Hi there,

This is all founded on good case leadership!

You need to develop your ability to drive the case forward.

To do so, you need to be extremely clear on the objective. Then, at every stage of the case you need to use frameworking to figure out the pathways of where you might go.

If you can determine what you need to calculate and why, then you can setup the general formula to get there and see what variables/data are missing!

This is extremely hard to learn on your own…if you're struggling, consider getting a coach to help you with the case (math) leadership!

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Ashwin
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replied on Jul 07, 2022
Ex Manager Bain and company | INSEAD

Hi there, 
Math portion of a case is heavily dependent on whether your equation solves the problem statement. Once you have laid out the equation correctly you have won 70-80% of the battle, the rest is assessing if I already have the data or do I need additional data or taking logical assumptions (in case of market estimation) to do the computation. I would suggest you focus on estimation drills to improve your ability to convert a problem into a math equation 

 

Thanks

Ashwin 

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Udayan
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replied on Jul 17, 2022
Top rated McKinsey Case & PEI coach/Multiple real offers/McKinsey EM in New York /6 years McKinsey recruiting experience

You have many great answers here to draw from.

In general, I would say the easiest way to know this is by first aligning on the approach with the interviewer. Once you do that it should become clearer what data points are needed to solve the question. It is also okay to ask for the data points once you start solving it.

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Francesco gave the best answer

Francesco

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