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Studies of firm-level data have shown that a firm's RD (2) productivity appears to depend on the intensity of parent firm RD and (3) spillovers of research effects from technologically related firms are significant but also depend on R&D intensity rather than total industry R&D. These results suggest that, despite the externalities created by spillovers of R&D, the `dilution' of R&D across multiple target plants reduces its potency sufficiently that spillovers may not be a source of industry-wide or economy-wide increasing returns.
Adams et al. (Mon,) studied this question.