Towards a valid bibliometric measure of epistemic breadth of researchers

The concept of epistemic breadth of the work of a researcher refers to the scope of their knowledge claims, as reflected in published research reports. Studies of epistemic breadth have been hampered by the lack of a validated measure of the concept. Here we introduce a knowledge space approach to the measurement of epistemic breadth and propose to use the semantic similarity network of an author's publication record to operationalize a measure. In this approach, each paper has its own location in a common abstract vector space based on its content. Proximity in knowledge space corresponds to thematic similarity of publications. Candidate measures of epistemic breadth derived from aggregate similarity values of researchers' bodies of work are tested against external validation data of researchers known to have made a major change in research topic and against self-citation data. We find that some candidate measures co-vary well with known epistemic breadth of researchers in the empirical data and can serve as valid indicators of the concept.