We propose a framework for analyzing transformations of demand. Such transformations frequently stem from changes in the dispersion of consumers` valuations, which lead to rotations of the demand curve. In a wide variety of settings, profits are a U-shaped function of dispersion. A high level of...

Firms selling multiple quality-differentiated products frequently alter their product lines when a competitor enters the market. We present a model of multiproduct monopoly and duopoly using a general `upgrades` approach that yields a powerful analytical framework. We provide a simple...

We present a general Cournot model in which each firm may sell multiple quality-differentiated products. We use an upgrades approach, working not with the actual products, but instead with upgrades from one quality to the next. The properties of single-product Cournot models carry over to the...

We study the effect of the fragmentation of intellectual property rights on optimal patent design. The major finding is that when several complementary innovative components must be assembled to operate a new technology, the patentability requirements should be stronger than in the case of...

We study a quality-ladder model of endogenous growth that produces stochastic leadership cycles. Over a cycle, industry leaders can innovate several successive times in the same industry, gradually increasing the magnitude of their technological lead before being replaced by a new entrant....