Macro-level changes in the structure of co-citation clusters: 1983–1989

This work uses a consistent method for clustering highly cited documents by single-link clustering and then clustering the resultant clusters, a total of four times, to give a hierarchical or nested structure of clusters four levels deep.

Abstract

At ISI we have used a consistent method for clustering the combinedScience Citation Index andSocial Sciences Citation Index for the last seven years (1983 to 1989). This method involves clustering highly cited documents by single-link clustering and then clustering the resultant clusters, a total of four times. This gives a hierarchical or nested structure of clusters four levels deep. Relationships among clusters at a given level can be depicted by multidimensional scaling, and by comparing successive year maps we can see how the relationships of major disciplines have changed from year to year. We focus mainly on the two highest levels of aggregation, C4 and C5, to make observations about structural changes in science involving the major disciplines. Distinction is made between changes which appear to be cyclic or oscillatory in nature, and those which appear to be more permanent or unidirectional.