What about the sub-types?
This might be a bigger question than this discussion but are participants chosen based on their subtypes? For example there are a lot of cancers. You can't include liver cancer and lung cancer patients in the same study (*without knowing who has what*) and give general results for cancer.
It's often baffling to see, for example, a study purportedly on "patients" with "bipolar disorder" with no mention made of which *type* of bipolar-disorder they have and, furthermore, of that specific *type* which of the symptoms from the laundry-list they had.