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Scientific research is performed within the context of an institution, and thus the recognition afforded the individual researchers affiliated with that institution is reflected in the prestige and reputation of the institution as a whole. By aggregating publications and citations at the institutional level we can measure the institutional output and prestige attributable to the affiliated researchers.

Counting method for papers and citations:

Institution counts are based on the author affiliations given on the published papers. A paper is attributed to an institution if the paper carries at least one author address of that institution. All addresses are considered, not only the first-listed author address. If an institution appears more than once on a paper, it is considered only once for paper and citation counts. All unique institutions on a paper are credited equally for the paper, and all citations received by a paper are credited equally to all the institutions on the cited paper. No restrictions are made on the citing items in compiling the citation counts, other than that they are recorded from Thomson Scientific-indexed journals only.

Time period for counts (cites, papers, cites per paper):

The time period for Essential Science Indicators counts is 10 years, plus partial year counts for the current year (data is updated six times a year). This means that any papers in the 10+ year period can be cited by any items in that same period. Thomson Scientific database years (the actual years when items are entered into the Thomson Scientific database, which is not necessarily the publication year) are used to define the time periods.

Types of items counted:

Papers are defined as regular scientific articles, review articles, proceedings papers, and research notes. Letters to the editor, correction notices, and abstracts are not counted. Only Thomson Scientific-indexed journal articles or papers are counted.

Journals included:

Essential Science Indicators counts are based on an Thomson Scientific journal set (see complete journal list for Essential Science Indicators) categorized into 22 broad fields. Fields are defined by a unique grouping of journals, with no journal being assigned to more than one field. The Multidisciplinary field contains journals such as Science and Nature which in an article level classification would be assigned to specific fields. This should be taken into account when analyzing the field ranking of an individual scientist, institution, or country.

Citation thresholds:

Institutions selected for listing in Essential Science Indicators must meet a cumulative citation count threshold for the 10+ year period. The thresholds are set separately for each field. More information about the actual thresholds used in Essential Science Indicators.

The absence of an institution's name in Essential Science Indicators means that the institution did not meet the citation threshold in any field.

Name conflation:

Institutions having the same name may represent more than one institution. This might be a similarly named institution in some other geographic location. Examining highly cited papers for such an institution will reveal whether institutions at different locations are involved.

Name variations:

Institutions may appear with different name abbreviations, in which case more than one entry may need to be consulted. In general, the name listed is as published with the exception of overt variants that have been identified, changed to a preferred form, and added to a unification dictionary. Unification (unifying the varying ways institutional names are given) is based only on the first segment of the author address. For example, the address HARVARD UNIV, BRIGHAM & WOMEN'S HOSP, would be given the unified name of the first segment only, ie, HARVARD UNIV.

Rank orderings:

Institutions in the rankings are numbered from 1 to N, depending on the ranking option selected, with no repeated ranks for ties (ties are then ranked alphabetically). Ranking options include citations, papers, citations per paper, and alphabetic. The citations per paper measure normalizes to some degree for the institution's output.