Case Interview: A comprehensive guide

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Now, back to the article!

2.1.1.One: Probing mind

Showing intellectual curiosity by asking relevant and insightful questions that demonstrate critical thinking and a proactive nature. For instance, if we are told that revenues for a leading supermarket chain have been declining over the last ten years, a successful candidate would ask:

“We know revenues have declined. This could be due to price or volume. Do we know how they changed over the same period? ”

This is as opposed to a laundry list of questions like:

• Did customers change their preferences?
• Which segment has shown the decline in volume?
• Is there a price war in the industry?

2.1.2. Two: Structure

Structure in this context means structuring a problem. This, in turn, means creating a framework - that is, a series of clear, sequential steps in order to get to a solution.

As with the case interview in general, the focus with case study structures isn’t on reaching a solution, but on how you get there.

This is the trickiest part of the case interview and the single most common reason candidates fail.

We discuss how to properly structure a case in more detail in section three. In terms of what your interviewer is looking for at high level, though, key pieces of your structure should be:

• Proper understanding of the objective of the case - Ask yourself: "What is the single crucial piece of advice that the client absolutely needs?"
• Identification of the drivers - Ask yourself: "What are the key forces that play a role in defining the outcome?"

Our Problem Driven Structure method, discussed in section three, bakes this approach in at a fundamental level. This is as opposed to the framework-based approach you will find in older case-solving

Focus on going through memorised sequences of steps too-often means failing to develop a full understanding of the case and the real key drivers.

At this link, we run through a case to illustrate the difference between a standard framework-based approach and our Problem Driven Structure method.

2.1.3. Three: Problem Solving

You’ll be tested on your ability to identify problems and drivers, isolate causes and effects, demonstrate creativity and prioritise issues. In particular, the interviewer will look for the following skills:

• Prioritisation - Can you distinguish relevant and irrelevant facts?
• Connecting the dots - Can you connect new facts and evidence to the big picture?
• Establishing conclusions - Can you establish correct conclusions without rushing to inferences not supported by evidence?

2.1.4. Four: Numerical Agility

In case interviews, you are expected to be quick and confident with both precise and approximated numbers. This translates to:

• Performing simple calculations quickly - Essential to solve cases quickly and impress clients with quick estimates and preliminary conclusions.
• Analysing data - Extract data from graphs and charts, elaborate and draw insightful conclusions.
• Solving business problems - Translate a real world case to a mathematical problem and solve it.

Our article on consulting math is a great resource here, though the extensive math content in our MCC Academy is the best and most comprehensive material available.

2.1.5. Five: Communication

Real consulting work isn’t just about the raw analysis to come up with a recommendation - this then needs to be sold to the client as the right course of action.

Similarly, in a case interview, you must be able to turn your answer into a compelling recommendation. This is just as essential to impressing your interviewer as your structure and analysis.

Consultants already comment on how difficult it is to find candidates with the right communication skills. Add to this the current direction of travel, where AI will be able to automate more and more of the routine analytic side of consulting, and communication becomes a bigger and bigger part of what consultants are being paid for.

So, how do you make sure that your recommendations are relevant, smart, and engaging? The answer is to master what is known as CEO-level communication.

This art of speaking like a CEO can be quite challenging, as it often involves presenting information in effectively the opposite way to how you might normally.

To get it right, there are three key areas to focus on in your communications:

1. Top down: A CEO wants to hear the key message first. They will only ask for more details if they think that will actually be useful. Always consider what is absolutely critical for the CEO to know, and start with that. You can read more in our article on the Pyramid Principle.
2. Concise: This is not the time for "boiling the ocean" or listing an endless number possible solutions. CEOs, and thus consultants, want a structured, quick and concise recommendation for their business problem, that they can implement immediately.
3. Fact-based: Consultants share CEOs' hatred of opinions based on gut feel rather than facts. They want recommendations based on facts to make sure they are actually in control. Always go on to back up your conclusions with the relevant facts.

For more detail on all this, check out our full article on delivering recommendations.

2.2.1. Application screen

It’s sometimes easy to forget that such a large cut is made at the application stage. At larger firms, this will mean your resume and cover letter is looked at by some combination of AI tools, recruitment staff and junior consulting staff (often someone from your own university).

Only the best applications will be passed to later stages, so make sure to check out our free resume and cover letter guides, and potentially get help with editing, to give yourself the best chance possible.

2.2.2. Aptitude tests and online cases

This part of the selection process has been changing quickly in recent years and is increasingly beginning to blur into the traditionally separate case interview rounds.

In the past, GMAT or PST style tests were the norm. Firms then used increasingly sophisticated and often gamified aptitude tests, like the Pymetrics test currently used by several firms, including BCG and Bain, and the original version of McKinsey’s Solve assessment (then branded as the Problem Solving Game).

Now, though, there is a move towards delivering relatively sophisticated case studies online. For example, McKinsey has replaced half the old Solve assessment with an online case. BCG’s Casey chatbot case now directly replaces a live first round case interview, and in the new era of AI chatbots, we expect these online cases to quickly become more realistic and increasingly start to relieve firms of some of the costs of live interviews.

Our consultants collectively reckon that, over time, 50% of case interviews are likely to be replaced with these kinds of cases. We give some specific advice for online cases in section four. However, the important thing to note is that these are still just simulations of traditional case interviews - you still need to learn how to solve cases in precisely the same way, and your prep will largely remain the same.

2.2.3. Rounds of Interviews

Now, let’s not go overboard with talk of AI. Even in the long term, the client facing nature of consulting means that firms will have live case interviews for as long as they are hiring anyone. And in the immediate term, case interviews are still absolutely the core of consulting selection.

Before landing an offer at McKinsey, Bain, BCG or any similar firm, you won’t just have one case interview, but will have to complete four to six case interviews, usually divided into two rounds, with each interview lasting approximately 50-60 minutes.

Being invited to first round usually means two or three case interviews. As noted above, you might also be asked to complete an online case or similar alongside your first round interviews.

If you ace first round, you will be invited to second round to face the same again, but more gruelling. Only then - after up to six case interviews in total, can you hope to receive an offer.

NB: No case without fit

Note that, even if you have only been told you are having a case interview or otherwise are just doing a case study, always be prepared to answer fit questions. At most firms, it is standard practice to include some fit questions in all case interviews, even if there are also separate explicit fit interviews, and interviewers will almost invariably include some of these questions around your case. This is perfectly natural - imagine how odd and artificial it would be to show up to an interview, simply do a case and leave again, without talking about anything else with the interviewer before or after.

2.5.1. Candidate led vs interviewer led case formats

Most consulting case interview questions test your ability to crack a broad problem, with a case prompt often going something like:

"How much would you pay to secure the rights to run a restaurant in the British Museum?"

You, as a candidate, are then expected to identify your path to solve the case (that is, provide a structure), leveraging your interviewer to collect the data and test your assumptions.

This is known as a “candidate-led” case interview and is used by Bain, BCG and other firms.

However, a McKinsey case interview - especially in the first round - is slightly different, with the interviewer controlling the pace and direction of the conversation much more than with other case interviews.

At McKinsey, your interviewer will ask you a set of pre-determined questions, regardless of your initial structure. For each question, you will have to understand the problem, come up with a mini structure, ask for additional data (if necessary) and come to the conclusion that answers the question.

McKinsey’s cases are thus referred to as “interviewer-led”. This more structured format of case also shows up in online cases by other firms - notably including BCG’s Casey chatbot (with the amusing result that practising McKinsey-style cases can be a great addition when prepping for BCG).

Essentially, these interviewer-led case studies are large cases made up of lots of mini-cases. You still use basically the same method as you would for standard (or candidate-led) cases - the main difference is simply that, instead of using that method to solve one big case, you are solving several mini-cases sequentially.

2.5.2. The McKinsey PEI

McKinsey brands its fit aspect of interviews as the Personal Experience Interview or PEI. Despite the different name, this is really much the same interview you will be going up against in Bain, BCG and any similar firms.

McKinsey does have a reputation for pushing candidates a little harder with fit or PEI questions, focusing on one story per interview and drilling down further into the specific details each time. We discuss this tendency more in our fit interview article. However, no top end firm is going to go easy on you and you should absolutely be ready for the same level of grilling at Bain, BCG and others. Thus any difference isn’t hugely salient in terms of prep.

2.6.1. Automated fit interviews

Analogous to online cases, in recent years there has been a trend towards automated, “one way” fit interviews, with these typically being administered for consultancies by specialist contractors like HireVue or SparkHire.

These are kind of like Zoom interviews, but if the interviewer didn’t show up. Instead you will be given fit questions to answer and must record your answer in your computer webcam. Your response will then go on to be assessed by an algorithm, scoring both what you say and how you say it.

Again, with advances in AI, it is easy to imagine these automated interviews going from fully scripted interactions, where all candidates are asked the same list of questions, to a more interactive experience. Thus, we might soon arrive at a point where you are being grilled on the details of your stories - McKinsey PEI style - but by a bot rather than a human.

We include some tips on this kind of “one way” fit interview in section six here.

3.2.1. Identify the problem

Identifying the problem means properly understanding the prompt/question you are given, so you get to the actual point of the case.

This might sound simple, but cases are often very tricky, and many candidates irretrievably mess things up within the first few minutes of starting. Often, they won’t notice this has happened until they are getting to the end of their analysis. Then, they suddenly realise that they have misunderstood the case prompt - and have effectively been answering the wrong question all along!

With no time to go back and start again, there is nothing to do. Even if there were time, making such a silly mistake early on will make a terrible impression on their interviewer, who might well have written them off already. The interview is scuppered and all the candidate’s preparation has been for nothing.

This error is so galling as it is so readily avoidable.

Our method prevents this problem by placing huge emphasis on a full understanding of the case prompt. This lays the foundations for success as, once we have identified the fundamental, underlying problem our client is facing, we focus our whole analysis around finding solutions to this specific issue.

Now, some case interview prompts are easy to digest. For example, “Our client, a supermarket, has seen a decline in profits. How can we bring them up?”. However, many of the prompts given in interviews for top firms are much more difficult and might refer to unfamiliar business areas or industries. For example, “How much would you pay for a banking license in Ghana?” or “What would be your key areas of concern be when setting up an NGO?”

Don’t worry if you have no idea how you might go about tackling some of these prompts!

In our article on identifying the problem and in our full lesson on the subject in our MCC Academy course, we teach a systematic, four step approach to identifying the problem, as well as running through common errors to ensure you start off on the right foot every time!

This is summarised here:

Following this method lets you excel where your competitors mess up and get off to a great start in impressing your interviewer!

3.2.2. Build your problem driven structure

After you have properly understood the problem, the next step is to successfully crack a case is to draw up a bespoke structure that captures all the unique features of the case.

This is what will guide your analysis through the rest of the case study and is precisely the same method used by real consultants working on real engagements.

Of course, it might be easier here to simply roll out one an old-fashioned framework, and a lot of candidates will do so. This is likely to be faster at this stage and requires a lot less thought than our problem-driven structure approach.

However, whilst our problem driven structure approach requires more work from you, our method has the advantage of actually working in the kind of complex case studies where generic frameworks fail - that is exactly the kind of cases you can expect at an MBB interview.

Since we effectively start from first principles every time, we can tackle any case with the same overarching method. Simple or complex, every case is the same to you and you don’t have to gamble a job on whether a framework will actually work

In practice, structuring a problem with our method means drawing up either an issue tree or an hypothesis tree, depending on how you are trying to address the problem.

These trees break down the overall problem into a set of smaller problems that you can then solve individually. Representing this on a diagram also makes it easy for both you and your interviewer to keep track of your analysis.

To see how this is done, let’s look at the issue tree below breaking down the revenues of an airline:

These revenues can be segmented as the number of customers multiplied by the average ticket price. The number of customers can be further broken down into a number of flights multiplied by the number of seats, times average occupancy rate. The node corresponding to the average ticket price can then be segmented further.

It is worth noting that the same problem can be structured in multiple valid ways by choosing different means to segment the key issues.

That said, not all valid structures are equally useful in solving the underlying problem. A good structure fulfils several requirements - including MECE-ness, level consistency, materiality, simplicity, and actionability. It’s important to put in the time to master segmentation, so you can choose a scheme isn’t only valid, but actually useful in addressing the problem.

After taking the effort to identify the problem properly, an advantage of our method is that it will help ensure you stay focused on that same fundamental problem throughout. This might not sound like much, but many candidates end up getting lost in their own analysis, veering off on huge tangents and returning with an answer to a question they weren’t asked.

Another frequent issue - particularly with certain frameworks - is that candidates finish their analysis and, even if they have successfully stuck to the initial question, they have not actually reached a definite solution. Instead, they might simply have generated a laundry list of pros and cons, with no clear single recommendation for action.

Clients employ consultants for actionable answers, and this is what is expected in the case interview. The problem driven structure excels in ensuring that everything you do is clearly related back to the key question in a way that will generate a definitive answer. Thus, the problem driven structure builds in the hypothesis driven approach so characteristic of real consulting practice.

You can learn how to set out your own problem driven structures in our article here and in our full lesson in the MCC Academy course.

3.2.3. Lead the analysis

A problem driven structure might ensure we reach a proper solution eventually, but how do we actually get there?

We call this step "leading the analysis", and it is the process whereby you systematically navigate through your structure, identifying the key factors driving the issue you are addressing.

Generally, this will mean continuing to grow your tree diagram, further segmenting what you identify as the most salient end nodes and thus drilling down into the most crucial factors causing the client’s central problem.

Once you have gotten right down into the detail of what is actually causing the company’s issues, solutions can then be generated quite straightforwardly.

To see this process in action, we can return to our airline revenue example:

Let’s say we discover the average ticket price to be a key issue in the airline’s problems. Looking closer at the drivers of average ticket price, we find that the problem lies with economy class ticket prices. We can then further segment that price into the base fare and additional items such as food.

Having broken down the issue to such a fine-grained level, solutions occur quite naturally. In this case, we can suggest incentivising the crew to increase onboard sales, improving assortment in the plane, or offering discounts for online purchases.

Our article on leading the analysis is a great primer on the subject, with our video lesson in the MCC Academy providing the most comprehensive guide available.

3.2.4. Provide recommendations

So you have a solution - but you aren’t finished yet!

Now, you need to deliver your solution as a final recommendation.

This should be done as if you are briefing a busy CEO and thus should be a one minute, top-down, concise, structured, clear, and fact-based account of your findings.

The brevity of the final recommendation belies its importance. In real life consulting, the recommendation is what the client has potentially paid millions for - from their point of view, it is the only thing that matters.

In an interview, your performance in this final summing up of your case is going to significantly colour your interviewer’s parting impression of you - and thus your chances of getting hired!

So, how do we do it right?

Barbara Minto's Pyramid Principle elegantly sums up almost everything required for a perfect recommendation. The answer comes first, as this is what is most important. This is then supported by a few key arguments, which are in turn buttressed by supporting facts.

Across the whole recommendation, the goal isn’t to just summarise what you have done. Instead, you are aiming to synthesize your findings to extract the key "so what?" insight that is useful to the client going forward.

All this might seem like common sense, but it is actually the opposite of how we relay results in academia and other fields. There, we typically move from data, through arguments and eventually to conclusions. As such, making good recommendations is a skill that takes practice to master.

We can see the Pyramid Principle illustrated in the diagram below:

To supplement the basic Pyramid Principle scheme, we suggest candidates add a few brief remarks on potential risks and suggested next steps. This helps demonstrate the ability for critical self-reflection and lets your interviewer see you going the extra mile.

The combination of logical rigour and communication skills that is so definitive of consulting is particularly on display in the final recommendation.

Despite it only lasting 60 seconds, you will need to leverage a full set of key consulting skills to deliver a really excellent recommendation and leave your interviewer with a good final impression of your case solving abilities.

Our specific article on final recommendations and the specific video lesson on the same topic within our MCC Academy are great, comprehensive resources. Beyond those, our lesson on consulting thinking and our articles on MECE and the Pyramid Principle are also very useful.

3.3.1. Estimation

Consultants need to push forward to provide definitive recommendations to clients in a timely manner despite typically not having access to full information on a problem. Estimation of important quantities is therefore at the heart of real life consulting work.

Estimation is thus just as fundamental to case cracking.

A case interview might centre on an estimation question, and this might be quite common for a first round interview. However, estimation is also very likely to be a crucial part of pretty well any other kind of case question you receive is likely to include estimation as a crucial component of your analysis.

The kinds of estimation you might be asked to make in a case interview can be very daunting:

Examples

• How many bank branches are there in Italy?
• How many cars are sold in Berlin in one year?
• How many people will buy the latest high-tech smartphone on the market?

You might have no idea where to begin with these examples. However, tempting as it might be, your answer cannot ever be a simple guess.

A decent estimation does have a guessed element - though this should really be an educated guess based on some pre-existing knowledge. However, this guessed element is always then combined with a rigorous quantitative method to arrive at a reasonable estimation.

In context of a case interview, it’s important to realise that your interviewer doesn’t really care about the right answer (they don’t need to ask you to find out, after all). What’s important is showing the rational process by which you get to your answer.

A guess that was somehow exactly correct is no good compared to a “wrong” answer that was reached by a very sensible, intelligent process of estimation. In cases, this method will often be a matter of segmentation.

So, where would we start in working out how many cars are sold in Berlin, for example?

The key to estimation case questions is the ability to logically break down the problem into more manageable pieces. In consulting case studies, this will generally mean segmenting a wider population to find a particular target group. For example, starting from the total population of Berlin and narrowing down to the cohort of individuals who will buy a car that year.

There are usually many ways to segment the same starting population, and several different segmentation schemes might be equally valid. However, it is crucial to choose the specific method best suited to the goal in answering the question and allowing you to best leverage the data you have available.

Segmentation must be allied with assumptions in order to arrive at an estimation. These assumptions are the “guessed” element of estimations we mentioned above. Assumptions cannot just be plucked from thin air, but must always be reasonable.

The example below showcases both the segmentation and assumptions made in an estimation of the size of the wedding planning market in London:

Our articles on estimation and the MECE concept are great starting points in getting to grips with consulting estimation. However, the best place to learn how to make estimations is with the dedicated building block video lesson in our MCC Academy course.