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When innovations are heterogeneous, it may be advantageous to provide a variety of patents. By trading off patent breadth for length, it is possible that fees are not needed in the optimal policy. We present two examples. The first is a quality-ladder model, in which innovations benefit society directly as well as through their use as building blocks to future inventions, and the rate of arrival for the future innovation is unobserved. More fertile innovations get more breadth for a shorter time. Menus may also be useful in the case of horizontal product differentiation. Copyright 2001 by the RAND Corporation.
Jaffe et al. (Mon,) studied this question.