Hello,

You shouldn't be asking for data in market sizing questions. However, don't worry too much about this as the interviewers will be looking to assess how you approach the problem, not the precise numbers that you come up with - i.e. they will be more interested in seeing that you are trying to use the number of patients per doctor as a data point, rather than what you estimate this number to be. 

I echo Ian's advice in how to approach a market sizing question you are stuck on - use your real-world experience and anything you may have seen in the news as a basis to come up with numbers that would seem plausible to you.