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What are research fronts? A research front is a group of highly cited papers, referred to as "core papers," in a specialized topic defined by a cluster analysis. Research fronts offer an alternative classification scheme for highly cited papers since the assignment of papers to a research front is not based on the journal categories used in Essential Science Indicators.

A measure of association between highly cited papers is used to form the clusters. (See the Highly Cited Papers section for an explanation of the selection criteria.) That measure is the number of times pairs of papers have been co-cited, that is, the number of later papers that have cited both of them. Clusters are formed by selecting all papers that can be linked together by a specified co-citation threshold.

The clusters are named using a semi-automatic process based on frequently occurring words and phrases. Statistical characteristics of each cluster are also determined, including the number of highly cited papers, the sum of their citation frequencies, the citations per paper, and the mean year of papers in the front. The number of highly cited papers gives an indication of the size of the foundation literature; the sum of citation frequencies reflects the size of the research front; the citations per paper the degree of concentration, and the mean year of papers the currency, or "hotness," of the cluster.

Field Classification:

Research fronts are assigned to the 22 broad fields based on the field of the most frequently occurring journal in the front.

Inclusion Criteria:

Only those fronts meeting a minimum size threshold and high average currency are included in Essential Science Indicators. Currency is determined by calculating the mean of the years of publications of the highly cited papers.

See complete journal list for Essential Science Indicators.