A feature of Essential Science Indicators is the reclassification of papers from multidisciplinary journals into the 22 Essential Science Indicators standard fields. Of the roughly 9,000 journals scanned for Essential Science Indicators, most are highly specialized and thus can be uniquely assigned to one of the fields (see Essential Facts). Approximately 60 journals, including journals such as Science, Nature, and the Proceedings of the National Academy of Sciences of the USA (PNAS), are classified as multidisciplinary since they publish research reports in many different fields. Until now, papers in these journals have been counted as Multidisciplinary despite the fact that many of them are highly specialized and represent research in specific fields, such as immunology, physics, neuroscience, etc.

Thus, an automated procedure was put into place, similar to one used for many years by the Research Services Group at Thomson Scientific: papers are assigned to a field based on the field representation of the citing journals and cited journals. For example, if the majority of the citations to a paper published in a multidisciplinary journal come from neuroscience journals and the majority of the cited references in the paper are to neuroscience journals, the paper will be assigned to neuroscience. In short, a paper is assigned to the field in which the largest number of its references and citations are classified.

This procedure is applied to the roughly 170,000 papers in the 60 multidisciplinary journals with the result that roughly one-half of the articles are reclassified in one of the Essential Science Indicators fields. The rate of reclassification varies widely with journal. For example, for Science, Nature, and PNAS, the average rate of reassignment is much higher—about 95 percent. The benefit of reclassification for Essential Science Indicators users is that statistics for fields, including author, institution, country, journal and paper rankings, more accurately reflect all papers in these fields, including those found in multidisciplinary journals, some of which publish influential, highly cited research reports.

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