One of the most common interview formats, especially for consulting firms, is the case interview.  It is also probably one of the most feared and difficult formats around. It requires specific and exhaustive preparation, quick thinking, keen insight, and intelligence. Yes, intelligence. Many a person who has passed regular interviews with flying colours and gotten fantastic job offers from good companies, has crashed and burned in the case interview, simply because they weren't smart enough. That's not to say that if you fail one, it's because you're dumb, but if you are not the sharpest knife in the drawer, you probably won't do very well. That's why consulting firms (and others) use them.

Case interviews are broadly defined as an interview geared around solving problems on the spot. A lot of companies give you the interview based on your resume, and they are really not interested in going through a one-hour re-hash of your experience as a camp counselor, and how it helped you become a leader. The resume part of your interview will either be cut partially or fully, in favour of a more real-life, nitty- gritty, "let's see how well you think" discussion. It cuts away from the B.S. about how you are detail-oriented 'cause you built some spreadsheet in your dad's office last summer, and gauges exactly how detail oriented you are, by giving you a problem and seeing you work it out. The form in which that problem is presented can take many forms, but in every case interview, the interviewer is trying to judge all or some of the following:

Logical Thought Process. How do you go about arriving at a solution, identifying key concepts, an orderly thought process, clearly separating important facts from irrelevant facts, analytical ability, are all factors which can impact the interviewer's assessment of your thought process.

General Business Knowledge and Acumen. Though no one wants to see you use Porter's Model (in fact don't use it at all), interviewer's want to see to what degree you have insight and knowledge of relevant issues in a business problem scenario - competitive threats, barriers to entry, competitive advantages, target marketing, pricing strategies, etc. Each case will have different concepts highlighted - the interviewer wants to make sure you can recognize which types of business analysis is appropriate for his specific case, as opposed to your trying to squeeze everything into some Model you learned in class as the end-all-and-be-all of human existence.

General Knowledge. In cases, there are a lot of times when the information you need will just not be available. This is not a problem, as the interviewer does not expect you to know them. However, you will have to make assumptions, and the degree to which your assumptions are reasonable will impact your performance. If, for example, you are conducting a market sizing example, and you say "Let's assume there are around 30 million people in Canada" - that's fine, the exact population is not needed. If, however, you say "Let's assume there are 100 million people in Canada", the interviewer might wonder what you've been smoking for the past eight years.

Comfort with Quantitative Analysis. No one will test you on differential calculus or statistical regression abilities - but if you can't figure out 10% of $250,000 in your head ($25,000), you'll be in trouble. Here the interviewer just wants to make sure you don't break into a cold sweat at the mention of a number, and that you can do some rough, back-of-the-envelope calculations accurately and quickly. It's just arithmetic - but you better know it. Quick, if you have 15% margins on a $20 good (widget?) that you're selling, and you sell 3,000 units - what was your profit?

Creativity. A new approach to a problem, an insightful remark, finding a hurdle that nobody else had noticed, using a strategy that worked for another company in a similar situation - this is what consultants do. If you can demonstrate some creativity, you will surely impress. This becomes more important in 2nd and 3rd round interviews, than in the 1st. Just make sure that in your quest for creativity, you don't come up with some ludicrous situation that make you sound like you have no idea what you're talking about. It's a fine line? Yes. Will you have to walk it? Yes.

Communication skills. You could be the most intelligent person in the world, but if you can't communicate your ideas, sell your ideas, and answer to criticism about your ideas, you will not be successful. Not in interviews - not in the business world either. There's no way around this one - learn to communicate!

Case interview questions are directed at assessing your ability to communicate, structure your thoughts, solve problems, and be creative. The solution to a case question is not necessarily as important as the process you go through to answer it. Many, but not all, consulting firms use case interviewing. On rare occasion firms in industry will use case questions, as well.

Brief review of answering Case Interview questions.
1.Ask questions; try to find out any relevant information up front.
2.State your assumptions, no matter how basic.
3.Develop a number of solutions.
4.Assess each solution individually, speaking your thoughts out loud, until you have determined that the solution is feasible or not.
5.If a solution becomes unfeasible, discard it and go to the next solution.
6.When you reach a feasible solution - STOP, unless the interviewer wants you to continue with other solutions.

On-line practice for case interviewing is available through the following consulting firms' web sites.
Boston Consulting Group
Wetfeet: