Henry Small

Co‐citation in the scientific literature: A new measure of the relationship between two documents

A new form of document coupling called co-citation is defined as the frequency with which two documents are cited together. The co-citation frequency of two scientific papers can be determined by comparing lists of citing documents in the Science Citation Index and counting identical entries. Networks of co-cited papers can be generated for specific scientific specialties, and an example is drawn from the literature of particle physics. Co-citation patterns are found to differ significantly from bibliographic coupling patterns, but to agree generally with patterns of direct citation. Clusters of co-cited papers provide a new way to study the specialty structure of science. They may provide a new approach to indexing and to the creation of SDI profiles.

Visualizing science by citation mapping

Science mapping is discussed in the general context of information visualization. Attempts to construct maps of science using citation data are reviewed, focusing on the use of co-citation clusters. New work is reported on a dataset of about 36,000 documents using simplified methods for ordination, and nesting maps hierarchically. An overall map of the dataset shows the multidisciplinary breadth of the document sample, and submaps allow drilling down to the document level. An effort to visualize these data using advanced virtual reality software is described, and the creation of document pathways through the map is seen as a realization of Bushs (1945) associative trails.

Clustering thescience citation index® using co-citations

Earlier experiments in the use of co-citations to cluster theScience citation Indey (SCI) database are reviewed. Two proposed improvements in the methodology are introduced: fractional citation counting and variable level clustering with a maximum cluster size limit. Results of an experiment using the 1979SCI are described comparing the new methods with those previously employed. It is found that fractional citation counting helps reduce the bias toward high referencing fields such as biomedicine and biochemistry inherent in the use of an integer citation count threshold, and increases the range of subject matters covered by clusters. Variable level clustering, on the other hand, increases recall as measured by the percentage of highly cited items included in clusters. It is concluded that the two new methods used in combination will improve our ability to generate comprehensive maps of science as envisioned byDerek Price. This topic will be discussed in a forthcoming paper.

Tracking and predicting growth areas in science

SummaryWe explore the possibility of using co-citation clusters over three time periods to track the emergence and growth of research areas, and predict their near term change. Data sets are from three overlapping six-year periods: 1996-2001, 1997-2002 and 1998-2003. The methodologies of co-citation clustering, mapping, and string formation are reviewed, and a measure of cluster currency is defined as the average age of highly cited papers relative to the year span of the data set. An association is found between the currency variable in a prior period and the percentage change in cluster size and citation frequency in the following period. The conflating factor of “single-issue clusters” is discussed and dealt with using a new metric called in-group citation.

CLUSTERING THE SCIENCE CITATION INDEX USING CO-CITATIONS. II. MAPPING SCIENCE

Previous attempts to map science using the co-citation clustering methodology are reviewed, and their shortcomings analyzed. Two enhancements of the methodology presented in Part I of the paper-fractional citation counting and variable level clustering—are briefly described and a third enhancement, the iterative clustering of clusters, is introduced. When combined, these three techniques improve our ability to generate comprehensive and representative mappings of science across the multidisciplinaryScience Citation Index (SCI) data base. Results of a four step analysis of the 1979SCI are presented, and the resulting map at the fourth iteration is described in detail. The map shows a tightly integrated network of approximate disciplinary regions, unique in that for the first time links between mathematics and biomedical science have brought about a closure of the previously linear arrangement of disciplines. Disciplinary balance between biomedical and physical science has improved, and the appearance of less cited subject areas, such as mathematics and applied science, makes this map the most comprehensive one yet produced by the co-citation methodology. Remaining problems and goals for future work are discussed.

Paradigms, citations, and maps of science: a personal history

Can maps of science tell us anything about paradigms? The author reviews his earlier work on this question, including Kuhns reaction to it. Kuhns view of the role of bibliometrics differs substantially from the kinds of reinterpretations of paradigms that information scientists are currently advocating. But these reinterpretations are necessary if his theory will ever be empirically tested, and further progress is to be made in understanding the growth of scientific knowledge. A new Web tool is discussed that highlights rapidly changing specialties that may lead to new ways of monitoring revolutionary change in real time. It is suggested that revolutionary and normal science be seen as extremes on a continuum of rates of change rather than, as Kuhn originally asserted, as an all or none proposition.

Specialties and disciplines in science and social science: An examination of their structure using citation indexes

The technique of co-citation cluster analysis is applied to a special three-year (1972–1974) file of theSocial Sciences Citation Index. An algorithm is devised for identifying clusters which belong to a discipline based on the percentage of source documents which appear in a disciplinary journal set. Clusters in three disciplines (economics, sociology and psychology) are identified using this algorthm. Clusters in a specialty of natural science (particle physics) obtained from the 1973Science Citation Index are compared and contrasted with the three groups of social sciences clusters. Certain common structural characteristics of the social science and natural science groups suggest that knowledge is developing in parts of the social science disciplines in a manner similar to the natural sciences.

MACRO-LEVEL CHANGES IN THE STRUCTURE OF CO-CITATION CLUSTERS: 1983-1989

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.

On the shoulders of Robert Merton: Towards a normative theory of citation

In a series of seminal studies Robert K. Merton created a coherent theoretical view of the social system of science that includes the salient features of the formal publication system, thereby providing a theoretical basis for scientometrics and citationology. A fundamental precept of this system is the view of citations as symbolic payment of intellectual debts. When this concept is merged with a complementary theory of the conceptual symbolism of citations, the possibility for a rapprochement of the normative and constructivist theories is achieved, where the dual function of citations as vehicles of peer recognition and constructed symbols for specific original achievements in science is realized. This new synthesis is embodied in a citation classification system, the citation cube, with dimensions of normative compliance, symbolic consensus, and disinterestedness (self-citation).

Update on science mapping : Creating large document spaces

Science mapping projects have been revived by the advent of virtual reality software capable of navigating large synthetic three dimensional spaces. Unlike the earlier mapping efforts aimed at creating simple maps at either a global or local level, the focus is now on creating large scale maps displaying many thousands of documents which can be input into the new VR systems. This paper presents a general framework for creating large scale document spaces as well as some new methods which perform some of the individual processing steps. The methods are designed primarily for citation data but could be applied to other types of data, including hypertext links.