Agree with the general remarks above comments by Guennael.

Specifically, my approach would be:

1. Start by clarifying what is meant by "physician". We will just assume Physician = general medical practitioner AKA family doctor working at general practice / clinic.
2. Make and clarify with interviewer the general assumption that at any one time supply of physicians in the US will be enough to meet demand, .i.e. there are no supply side constraints given the well-functioning educational system / level of prosperity in the US etc.
3. Identify key “direct” drivers of number of physicians in the US. Not indirect drivers.
4. Two key direct drivers that need to be broken down are the 1) the demand for physician services divided by 2) the capacity per physician
   1. Demand for physicians visits per year = Size of population * # average number of illness events” per person per year * % of such illness events, which are serious enough to require a physician * % of such illness events that actually result in a visit to physician (why would people not go to a physician if they require it? 1) Financial reasons 2) Some are too busy and just cope somehow.
      1. Increase final result a bit to adjust for the fact that 1) especially the very young and the elderly part of the population visit physicians for routine check-ups even though they are not ill and 2) people might visit physicians for guidance on a broader set of “personal health matters” than just specific illnesses.
   2. Capacity per physician per year = Average #of patients that can be attended to per physician per hour * working hours per physician per day *opening days per week * 4 weeks per month * 12 months per year
      1. Decrease final result a bit to adjust for “seasonality” / that the physicians also go on vacation / get ill etc.
5. Perform reasonableness check of final result.

Hope you find it useful and that I am not completely wrong :)

You could approach it a varieties of ways - we don't care which one you chose, as long as it is consistent / MECE and you quickly drive to a reasonable answer. For example (off the top of my head in the time it takes me to write this):

- How many people in the US, how many clients can a MD see?

- How many people in the US, average salary of physician is X, average profit per visity is Y

- How many physicians in my town, how many people in my town, how many people in the US

- How many medical schools in US, how big are classes, how many years a typical physician practices medicine before retiring

I'm sure you can think up a few more ways to address the question on your own. Just make sure you end result is neither "10 doctors in the US" nor "250 million physians" :)

Cheers,

Guennael

ex-BCG Dallas