I have recently done my first ever market sizing case study interview (not MBB, second tier). As I don't know how good is good enough, I'd appreciate your opinions on how you think I fared, based on the following:- I set out a clear, logical and typical approach: take population, segment by age, ascertain # of consumers and consumption per head => mkt volume, estimate unit value => get mkt value.- I performed some tricky mental calculations quickly and accurately (e.g. translate 2/80 to a percentage - not rocket science, but we all know the tricks nerves can play).However, I had a couple of hiccups. I made one silly calculation error (2.5% of 50 - I know, primary school stuff), but as soon as I heard the words, "are you sure?" I rectified and corrected.Also, I proposed an estimation of a manufacturer's revenue based on retail price. But again, once I saw the raised eyebrow of my interviewer, I realised I forgot to take out distrib/retail margin, rectified and corrected.So how did I do? How serious are this hiccups, considering the rest was ok?

If that is all you are worried about, you should be fine.It is perfectly acceptable to have hiccups in case-study under 30mins that will take you about 2 days to do in real life. Better still, ones that you self-corrected.

Thanks BC.As there are candidates who buy case-study books, go on courses, practise with friends, and have done many interviews, I imagined many of them would end up being able to go in and rock out an exercise like this flawlessly. Hence, I was quite disappointed, especially having gotten my head round the problem, only to let silly mistakes and oversights let me down.

I think such hiccups are absolutely acceptable. As Big Consultant said, in real life, people take about 2 days for such stuff. By the way, you should have got your results by now:) - what happened?

Having overseen one of these recently (proj mgt case studies, not market sizing), I can tell you that the process is just as important as getting to the right answer. Self-correcting and being able to take feedback (while not breaking down with nerves) are key strengths in an analyst. Being too smooth and "flawless" (which no case study is) invites the reviewer to pick on underlying details (how do you KNOW this assumption is true, what external information would you need to validate this?). Let us know how you did, but knowing what you did wrong and acknowledging it to the reviewer does not reflect badly on your performance at all.

I hold case studies for candidates, between 50 and 70 per year (to give you a sense of scale).Everyone makes mistakes, but actually that misses the point. Very roughly we score like this:1. Was the brief understood and does the individual 'get it'2. Was the presentation credible and relevant.3. Could the candidate defend his position or did he/she crack?Obviously its not as arbitrary as that, but thats a guide.As interviewers and assessors we're not stupid. We recognise talent and actually its in our interests to see if you CAN not if you CAN'T.You'll be fine.