Knowledge appropriability, firm size, and growth

Empirical evidence shows that the number of patents per R&D dollar declines with firm size. In this paper, we propose a Schumpeterian growth model that accounts for this evidence. We analyze an economy with firms that engage in cost-reducing innovation resulting from the accumulation of both codified and tacit knowledge: the former occurs through the purchase of patents, while the latter is the result of R&D conducted in-house by firms. We study the relation between knowledge appropriability and market structure, and we show that a shift from patents to in-house research occurs as firm size gets larger. Since innovation statistics concentrate mainly on patents, this process of research reallocation results into an under-estimation of innovative activity and is responsible for the declining ratio of patents to R&D expenditure. Survey data on UK-based firms provide support to our results.