AbstractPurposeTo give a theoretical framework to measure the relative impact of bibliometric methodology on the subfields of a scientific discipline, and how that impact depends on the method of evaluation used to credit individual scientists with citations and publications. The authors include a study of the discipline of physics to illustrate the method. Indicators are introduced to measure the proportion of a credit space awarded to a subfield or a set of authors.Design/methodology/approachThe theoretical methodology introduces the notion of credit spaces for a discipline. These quantify the total citation or publication credit accumulated by the scientists in the discipline. One can then examine how the credit is divided among the subfields. The design of the physics study uses the American Physical Society print journals to assign subdiscipline classifications to articles and gather citation, publication, and author information. Credit spaces for the collection of Physical Review Journal articles are computed as a proxy for physics.FindingsThere is a substantial difference in the value or impact of a specific subfield depending on the credit system employed to credit individual authors.Research limitationsSubfield classification information is difficult to obtain. In the illustrative physics study, subfields are treated in groups designated by the Physical Review journals. While this collection of articles represents a broad part of the physics literature, it is not all the literature nor a random sample.Practical implicationsThe method of crediting individual scientists has consequences beyond the individual and affects the perceived impact of whole subfields and institutions.Originality/valueThe article reveals the consequences of bibliometric methodology on subfields of a disciple by introducing a systematic theoretical framework for measuring the consequences.