E-Index - A Bibliometric Index of Research Efficiency.

A principal investigator is obligated not only to make academic impacts but also to do so in a cost-effective fashion. While popular bibliometric measures such as the journal impact factor (IF) and the H-index measure citation-oriented bibliometric impacts, here we propose the E-index to reflect a principal investigator's research efficiency also in terms of bibliometric data. Our E-index incorporates both IF-citation-based output and "total equivalent time" that the principal investigator's team takes to deliver the output so that the bibliometric output can be normalized by the involved research time. The E-index is then evaluated using a large set of peer-reviewed journal papers by extramurally funded Chinese principal investigators in the field of life sciences. The E-index values are compared relative to university rank and other factors. As expected, the highest average E-index scores were achieved by principal investigators at top national universities. Being quantitative, the E-index adds insight into common debates such as what the optimal team size should be, which career stage is the most prolific, and so on. The E-index should be useful in assessing principal investigators in comparable fields and longitudinally.