A methodology for cluster analysis of citation histories

Citations to all the papers (558) published from 1955 to 1964 by a multidisciplinary (natural sciences) research institute within a ‘scientific periphery’ were collected for the 11-year period after a 10-year lapse since the publication years. All the papers were grouped into 31 research topics, three of which had no such late citations at all. For the remaining 28 groups of papers three indicators were defined: ALPHA, the ratio of the number of papers with citations, to the number of all papers of the particular research topic, indicating thus an overall CITATION EFFICACY; BETA, the ratio of the sum of all citations, to the number of the cited papers, indicating CITATION INTENSITY, and GAMMA, expressing the CITATION LONGEVITY for a given research topic as the incidence (number) of cited papers (irrespective of the number of citations) within the 11-year citing period. In addition, three normalized transformations of the indicator BETA were checked. Two-dimensional (without ALPHA) and three dimensional (with ALPHA, GAMMA, and one of the BETA variants) graphical representations together with a pairwise correlation analysis served as preliminary guidance in the latter statistical analyses by (a) Ward's Hierarchical Cluster Analysis and (b) Polar Taxons Analysis. Both of them resulted in good agreement. Thus, the 28 research topics were found to belong to three clusters. Their composition varied slightly for the original BETA and its three normalized values. It was concluded that ALPHA is not a redundant but quite useful indicator, and that one of the normalized BETA-variants appears most suitable for this kind of studies. In the three-dimensional graphs the clusters may be related to scientific merit as judged in a composite way by all the three indicators. This is done with regard to the diagonal joining the indicators' maximal with their minimal values. The citation LONGEVITY (GAMMA) appears to be most important. Cluster stability tests showed fluctuations of few research topics, which was related to their specific features within the given research setting. It emerges on the whole that the research merit of this (peripheral) scientific production is determined neither by the journals status the papers were published in, nor by the authors' institutional status. Rather, it is the very scientific quality of individual papers within a given research topic that is decisive for the citation ‘survival’.