Within-firm productivity growth depends on changes in efficiency and the intensity with which inputs are used in production. Shifts in market shares among continuing firms reflect resource reallocation, and affect aggregate productivity trends if, for example, market shares of high or low productivity firms change. The process of entry and exit of firms is another form of reallocation, which contributes to aggregate productivity growth to the extent that more productive new firms displace the low productive exiting ones. The overall contribution of reallocation to productivity growth is generally viewed as reflecting a competitive process taking place in the market, although it may also reflect changes in demand conditions and may also be an aspect of technological progress