Final answer:
The HMO model where physicians keep their own practices while being part of a group is the Independent Practice Association (IPA) model.
Step-by-step explanation:
The type of HMO model that consists of physicians with separately owned practices who formally organize into a group but continue to practice in their own offices is the Independent Practice Association (IPA) model. In this model, the HMO contracts with a network of individual practices who agree to see HMO members under the terms of the contract. Physicians in an IPA can still maintain their own offices and treat non-HMO patients.