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Design 3. At entry, patients are randomized to initial treatments A1, A2 and A3. If a patient responds to the initial treatment she stays on the same initial treatment, otherwise the patient is re-randomized to subsequent treatments: A2 or A3 if she does not respond to A1; A1 or A3 if she does not respond to A2; A1 or A2 if she does not respond to A3.
