The definition and calibration of biomedical subfields

This paper first explains the need to define subfields of science by means of "filters" that selectively retrieve papers from a database, and then describes how such filters are constructed and calibrated. Good filters should have precision and recall of the order of 90% so as to be representative of a subfield; they are created by an interactive partnership between an expert in the subject and a bibliometrician. They are based primarily on the use of title keywords, often in combination rather than singly, and specialist journals. Their calibration depends on experts marking lists of papers extracted by the filter as relevant, don't know or not relevant. This allows the actual size of a subfield to be estimated and hence the relative importance accorded to it within a major field of science. It permits organisations and countries to see their contributions to individual scientific subfields in detail.