Brainstorming in a case interview

Brainstorming is a crucial part of any consulting case interview. It is a way for the interviewer to assess your ability to think creatively and structure your thoughts in a logical, MECE (Mutually Exclusive, Collectively Exhaustive) manner.

While it may seem daunting, with practice and the right approach, you can excel at brainstorming questions and impress your interviewer with broad, deep, and creative answers.

Brainstorming vs. frameworks

Brainstorming questions are similar to framework questions at the beginning of a case interview in that both aim to structure your thoughts on a topic. However, while framework questions are often broad and open-ended, brainstorming questions are more specific and require you to generate ideas to address a particular problem or opportunity.

Both frameworks and brainstorming questions can be investigative or prescriptive. Investigative questions require you to explore a problem and come up with potential causes and solutions, while prescriptive questions require you to recommend a course of action based on a set of facts and assumptions.

Elements of a great brainstorming answer

A great answer to a brainstorming question should be broad, deep, MECE, and insightful. It should cover the problem fully and have enough ideas that support each top-level bucket in two or even three levels of granularity. It should also be based on hypotheses that are tailored to the current situation in the case and include creative ideas on top of more commonsense and standard ones.

The interviewer might ask you:

What reasons can you think of that would lead to machines breaking down in different intervals at different locations?

Investigative brainstorming question

If we look at the sample answer above it is:

• Broad: Covers the problem from multiple angles
• Deep: Breaks each top-level down into several sub-buckets and even more concrete ideas below
• Insightful: While some ideas are commonsense, others are more creative
• MECE: The problem is covered and there are no overlaps

A bad answer on the other hand is one where the candidate immediately yells out ideas in no particular order or structure, neglecting interdependencies and forgetting to bucket their ideas. This is bad both in terms of problem-solving and communication.

Idea generation techniques for brainstorming

There are several techniques you can use to generate ideas for a brainstorming question to come up with an exhaustive and creative answer:

1. Mind mapping: Start with a central idea and branch out to related ideas.
2. Linking of ideas: Look for connections between different ideas and build on them.
3. Expansion of ideas: Take an idea and explore it in more depth to generate additional ideas.

Using a combination of these techniques can help you come up with a more diverse range of ideas and improve the quality of your answer. Sometimes, you might want to think about a brainstorming answer in a more top-down manner, starting with the top buckets, then expanding into lower-level ideas. This is useful when you want to use more concrete examples that could support a top-level bucket. Other times, it might be easier for you to go and create your answer bottom-up starting with more concrete ideas and then aggregating it into a more general top-level bucket. Most often, you will likely combine both approaches for the same answer.

Approach to brainstorming in a case interview

To excel at brainstorming questions in a consulting case interview, it is essential to have a structured approach. I would always follow the same approach as for any other structuring or framework question, consisting of four steps:

1. To start with, it’s important to understand the question properly, so if you’re unsure, paraphrase the question back to the interviewer and ask for confirmation.
2. Once you have a clear understanding of the question, politely ask for some time to think about it. In McKinsey interviews, you have around 2 minutes of time to think, and in candidate-led interviews around 1 minute, sometimes even 1.5 minutes. If you take less time, you will not have enough ideas (being broad and deep), not enough creative ideas (being insightful), and no structure (no top-down and structured communication). During this time, you need to come up with your structured list of ideas, combining the thinking and idea-generation techniques I described above.
3. After creating your MECE structure, present it top-down, starting with the main areas and then going deeper into each bucket, discussing the ideas on the lower levels that support the main buckets (numbered, signposted, and top-down).
4. Discuss what you would want to prioritize or what idea you think is the most likely/best (based on the case) and automatically highlight how this integrates into the case as a whole and where to go next.

During the conversation, if the interviewer provides any feedback, try to integrate their ideas into your structure and build on them. Remember, the interview is a conversation, and it’s essential to engage with the interviewer and be open to feedback. Interviewers might ask “What else?” or steer you in a particular direction “Have you considered X?”

Interviewers might also probe if you are demonstrating knowledge of the relevant industry and the client’s situation, whether you are making connections between different pieces of information provided in the case, whether you are presenting their ideas confidently and convincingly, and whether they are proposing feasible solutions that align with their hypothesis or hypotheses in the context of the case.

Tips for practicing brainstorming for a case interview

1. Get feedback from others: It can be incredibly helpful to practice brainstorming with a partner or group and get feedback on your structure and ideas. This can be a fellow candidate, a coach, or even a friend or family member who is willing to ask and listen. Make sure to ask for specific feedback on what worked well and what could be improved.
2. Use real-life examples: One way to improve your brainstorming skills is to practice with real-life examples. Take a news article, case study, or business problem and try to come up with a structure and ideas for how to solve it. This will help you build your industry knowledge organically and develop a more nuanced understanding of how to approach different types of problems.
3. Embrace creativity: While it’s important to have a structured approach to brainstorming, don’t be afraid to think outside the box and come up with creative ideas. Sometimes the best solutions come from unexpected places. Challenge yourself to think beyond the obvious and consider alternative perspectives. In doubt, the number of creative ideas that you can come up with is always more important than the way you bucket them.
4. Work on isolated drills: Instead of always looking at full cases, rather focus on isolated drills for each element of the case. This is also true for brainstorming questions. Take a set of 5-10 brainstorming questions and go through them one after the other, also practicing the communication aspect, not just the thinking part. This approach is much more effective than full case drills if you only want to work on one aspect, as it allows you to jump quickly from problem to problem and see a lot of problems in a short amount of time. This not only improves your idea-generation muscle to go broad, deep, and insightful but also your structured communication skills.
5. Practice under pressure: In a consulting case interview, you’ll likely be under time pressure to come up with a structured and insightful answer. To simulate this environment, try practicing brainstorming questions with a timer and see how quickly you can come up with a quality answer. This will help you build your speed and efficiency while still maintaining a high level of quality.
6. Optimize your note-taking: If you only have 1 minute to write down your answer, use shortcuts in writing (e.g., Profit = P) to maximize the time you spend thinking rather than writing. On top of that, become comfortable with creating ideas on the go. My experience shows that on average a candidate has 70-80% of their answer ready when they start talking. They figure out the remaining 20-30% once they start presenting their answer.
7. Reflect on your performance: After each practice session, take some time to reflect on your performance and what you can do better next time. Did you struggle with generating ideas? Did you have trouble structuring your answer in a clear and concise way? Use this feedback to improve your approach and build your skills over time. You could create an error or issue log with problems you struggled with or just general answers to typical brainstorming questions. For instance, there are three core ways to increase customer satisfaction (1. decrease waiting times 2. increase service level or product quality 3. decrease price). If you have used this once, you can use it again and tailor it to the specific question (e.g., airline passengers would have different lower-level buckets than guests in a restaurant). Memorized brainstorming answers do not work, the same as memorized case frameworks.

How we can help you ace your case interview

We have specialized in placing people from all walks of life with different backgrounds into top consulting firms both as generalist hires as well as specialized hires and experts. As former McKinsey consultants and interview experts, we focus on teaching the best habits and strategies to ace every case interview, including idea generation, problem-solving, and brainstorming, all from a first-principles perspective.

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