Hi Charlie,
Here is the difference:
Advanced:
means that you get a PGY year 2-4. Your internship is not
included at all. You may do your internship pretty much wherever
you choose that you can get. IF you get an advanced
you must be able to get either a prelim or a transitional for your
internship to compliment it
Categorical:
there are much fewer of these programs out there. This means
that your internship is included at the same institution as you will
be doing your derm residency. It's more of a "one stop shopping"
type of deal. If you get it you're there for the duration.
Hope this helps. You have to have an internship either way. The only difference is where you do it/if it is included in your derm appointment. You have to have one PGY1 year under your belt before derm, but it doesn't matter if it is at the same place or not.
All the best
,
Stax