Bibliometric performance and uncertainty inheterogeneous research groups: trends inauthorship and fractional citation indicators

Bibliometric indicators are widely used to evaluate scientific performance, despitewell-known limitations related to disciplinary differences, collaboration practices,and strategic responses to evaluation systems. Traditional metrics such as theH-index are particularly sensitive to the number of co-authors and to the lengthof reference lists, both of which have exhibited strong historical growth.This study analyzes the temporal evolution of authorship, referencing, and pro-ductivity patterns in six research populations (four Italian Scientific DisciplinarySectors in engineering and two international conference communities), cover-ing 1,286 researchers and 86,351 publications. The results reveal systematicincreases in authors per article, references per article, and documents per author,with structural changes that coincide with technological developments and theintroduction of bibliometric criteria in national evaluation policies.Building on fractional counting, we propose a new citation-based indicator inwhich publication credit is shared among co-authors and each incoming citationis weighted by the inverse of the number of references in the citing article. Com-parisons with the H-index show strong overall correlations, but indicate that theproposed indicator attenuates the advantage associated with hyper-authorshipand inflated reference lists and reduces variability across heterogeneous researchgroups.Adopting a measurement-theoretic perspective, we further assess the uncertaintyof bibliometric indicators by analyzing linear trends with researcher seniority andthe dispersion of individual data around these trends. The proposed indicator exhibits lower root mean square errors and more homogeneous slopes than the H-index, suggesting that it provides a more robust and comparable representationof scientific performance across diverse research communities.