Patent Citations and the Size of Patented Inventions - Evidence from Hybrid Corn

Abstract:     
Although most empirical analyses use patents as a measure of innovation, patents may be noisy and biased due to unobservable variation in the size of patented inventions. Patent citations – counts of later patents that cite a patent as relevant prior art – have become the standard measure to control for such variation, but citations themselves may be noisy and biased. To address this issue, we match patents for hybrid corn with data on yields, as an objective measure for the size of patented improvements. These data reveal a robust positive correlation between citations and improvements in yields, suggesting that citations are a good measure for size. The data also show that inventors and examiners frequently cite a small group of early patents, as ‘prior art’ to establish patentability. Excluding these patents strengthens the correlation between citations and the size of patented inventions.

Number of Pages in PDF File: 38

Keywords: innovation, patents, intellectual property, hybrid corn

JEL Classification: O30, O31, O33, O34, L70, Q10

working papers series