Phases of clinical trials

The categorization of clinical trials into phases I-IV (see Box 3.1) has its origins in drug development, but serves as a useful framework to describe the typical stages of development of any form of treatment. It is, however, increasingly rare that a new therapy would be evaluated in just one trial of each phase, and the distinctions between the phases have perhaps become less clear in practice than the conventional description would suggest. The main focus of this book is the randomized phase III trial. However, in this chapter we discuss some of the issues in the design of phase II studies and non-randomized phase III trials which do not appear elsewhere and which set the discussions

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