Recent years have seen a reorganisation of innovation production to favour groups of collaborators, and increasingly specialised individual inventors. In this paper I construct a panel of highly prolific inventors, whom I observe frequently throughout their career. I develop a simple setting whereby inventors face a trade-off between acquiring knowledge depth and knowledge breadth. Empirically, I provide suggestive evidence that after conditioning upon the selection of inventors into specialised careers in certain technological fields, specialisation is associated with a lower probability of contributing to a top-cited invention over the remainder of their career. This suggestive evidence is consistent with a mechanism where specialised inventors are vulnerable to knowledge obsolescence in the late stages of their career. The negative relationship between specialisation and highly cited inventions is concerning given the disproportionate value of such inventions to society. • I create a novel dataset on the careers of prolific inventors. • I integrate career cycle effects into the study of specialisation and productivity. • I develop a measure of specialisation at the inventor-field-year level. • I find specialisation is negatively linked to contributing to top-cited inventions. • I present evidence that this is consistent with a knowledge obsolescence mechanism.
Jordan Bisset (2026) studied this question.