Evolution of research portfolios of universities and heterogeneity in the returns to research specialization

Science is a dynamic process involving actors at different scales: from papers to countries going through authors and institutions. Nonetheless, the role of institutions - which is critical for assessing impact of some policies - has been largely understudied. To bridge this gap, we study the scientific portfolio of 26 institutions across the globe in the period 2000-2020. By analyzing 2.4 Mi papers, we find a correlation between portfolio dynamism and diversification, with more dynamic institutions tending to produce research across a broader range of non-related topics. Additionally, we find that not all research topics are equal in terms of impact: High-yielding topics show a significantly positive correlation between relative specialization and scientific impact per paper and are concentrated around a few research areas. Our results reveal robust patterns in university portfolio evolution that open the door to the development of mechanistic theories that explain the effect of university policies in the evolution of their portfolios.