Coping with the problem of subject classification diversity

The delimitation of a research field in bibliometric studies presents the problem of the diversity of subject classifications used in the sources of input and output data. Classification of documents according to thematic codes or keywords is the most accurate method, mainly used in specialised bibliographic or patent databases. Classification of journals in disciplines presents lower specificity, and some shortcomings as the change over time of both journals and disciplines and the increasing interdisciplinarity of research. Differences in the criteria in which input and output data classifications are based obliges to aggregate data in order to match them. Standardization of subject classifications emerges as an important point in bibliometric studies in order to allow international comparisons, although flexibility is needed to meet the needs of local studies.