Essential Science Indicators - Highly Cited Papers
Generally, citations to papers peak in the second, third, or fourth year after publication, but some papers continue to be cited for many years. A few papers can exhibit delayed recognition. The patterns can vary greatly depending on the type of paper, the field, and the nature of the finding reported. Papers reporting discoveries, for example, can rise quickly and then fall as the discovery is further elaborated in other articles. Papers reporting methods or techniques can gradually increase in citation frequency over several years as the methods diffuse throughout the community and prove their utility.
Selecting Highly Cited Papers
Since citation rates vary by field and older papers are cited more than recent papers, the selection procedure for highly cited papers takes these factors into account. The first step is to count the number of papers cited at different levels of citation and construct distributions for each field and year. These distributions for each field/year are then used to set selection thresholds by taking the same fraction of papers.
Time Period for Counts
The time period for counts is 10 years, plus partial year counts for the current year (data is updated every two to four months). This means that any papers in the 10+ year period can be cited by any items in that same period. Citations from all sources are counted, and are cumulated from the year of publication through the current year. Database years (the actual years when items are entered into the database, which is not necessarily the publication year) are used to define the time periods.
Citation cutoffs specific to field and year are applied to all papers in the journal set to select highly cited papers. Citation thresholds are based on the distribution of citations, picking the specified top fraction of papers for each year and field. The thresholds are based on the cutoffs given in the All Years column of the Baseline Percentiles table.
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 papers from journals covered by Web of Science Core Collection are counted.
Counts are based on a journal set 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/territory.