Hi there,

I think you're getting terminology mixed up :)

Issue trees have nothing to do with market sizing. Issue trees are primarily used for solving cases (and real life projects).

I think you're asking if you can break down the problem with sections/branches/trees. If that is the question, then yes you always should! You always need to setup the overarching math/calcs.

Depending on the market sizing, either top down or bottom up will be better…it depends!

How to Market Size

Remember that there's rarely a "best" answer with market sizing. What's important is that you break down the problem the way it makes sense to you. Importantly, break it down so that the assumptions you make are the ones you're most comfortable in.

For example, do you know all the major brands? Great go with that. Do you understand all the segments of that country's population (either age or wealth or job breakdown)? Go with that. Do you know the total market size of the tourism (or hotel) industry? Then break it down that way.

Some tips:

1. Just like in a case, make sure you understand the question - what are you really being asked to calculate
2. Decide whether a top-down or bottom-up approach is best
3. Figure out what you know you know, and what you know you don't know, but could estimate
   1. This helps you determine how to split out buckets
4. Stay flexible - you can start with a "high-level" market sizing, but gauge your interviewers reaction....if it looks like they want you to do more...then go along level deeper in terms of your splits

Here's some practice: https://www.preplounge.com/en/management-consulting-cases/interviewer-led-mckinsey-style/intermediate/taxis-in-manhattan-market-sizing-229