The Disruption Index Suffers From Citation Inflation and Is Confounded by Shifts in Scholarly Citation Practice

We demonstrate that the disruption index (CD) recently applied to publication and patent citation networks (Funk et al., Management Science 2017 [1]; Park et al., Nature 2023 [2]) systematically decreases over time due to secular growth in research and patent production, following two distinct mechanisms unrelated to innovation – the first structural and the second behavioral. The structural explanation follows from ‘citation inflation’ (CI) [3], an inextricable feature of real citation networks. One driver of CI is the ever increasing length of reference lists, which causes the CD index to systematically decrease. The behavioral explanation reflects shifts associated with techno-social factors (e.g. self-citation practices and software in- novations facilitating literature search, retrieval and citation management) that increase the rate of triadic closure in citation networks and confounds efforts to measure disruptive innovation using CD. Combined, these two mechanisms render CD unsuitable for cross-temporal analysis, and call into question the interpretations provided by Park et al. [2]