Bibliometric statistical properties of the 100 largest European universities: prevalent scaling rules in the science system

For the 100 largest European universities we studied the statistical properties of bibliometric indicators related to research performance, field citation density and journal impact. We find a size-dependent cumulative advantage for the impact of universities in terms of total number of citations. In previous work a similar scaling rule was found at the level of research groups. Therefore we conjecture that this scaling rule is a prevalent property of the science system. We observe that lower performance universities have a larger size-dependent cumulative advantage for receiving citations than top-performance universities. We also find that for the lower-performance universities the fraction of not-cited publications decreases considerably with size. Generally, the higher the average journal impact of the publications of a university, the lower the number of not-cited publications. We find that the average research performance does not dilute with size. Large top-performance universities succeed in keeping a high performance over a broad range of activities. This most probably is an indication of their scientific attractive power. Next we find that particularly for the lower-performance universities the field citation density provides a strong cumulative advantage in citations per publication. The relation between number of citations and field citation density found in this study can be considered as a second basic scaling rule of the science system. Top-performance universities publish in journals with significantly higher journal impact as compared to the lower performance universities. We find a significant decrease of the fraction of self-citations with increasing research performance, average field citation density, and average journal impact.