Essential Science Indicators rankings are based on a selection of the most cited scientists, institutions, countries, and journals in a ten-year period. To compensate for varying citation rates across scientific fields, different thresholds are applied to each field. The thresholds are set to select roughly the same proportion of entities from each field. For scientists the top 1% of names is selected for each of the fields. This percentage of inclusion translates into a specific citation frequency cutoff for each field. For institutions this percentage is also 1%, but for countries and journals 50%.
View: Citation Thresholds for Scientists, Countries, Institutions, and Journals.
Updated: January 1, 2008

Thresholds are also set to select highly cited papers to be listed in Essential Science Indicators. In this case different thresholds are set for both field and year of data. Setting different thresholds for each year period allows comparable representation for older and younger papers for each field. For each field and time period the top 1% of papers is selected. This table shows the citation count thresholds for each field and year corresponding to this top cut. In the selection process the appropriate threshold is compared against the cumulative citation count for each paper.
View: Highly Cited Papers Thresholds.
Updated: January 1, 2008

The selection of Hot Papers in Essential Science Indicators is similarly based on selecting the top cited papers in different fields, but the time frame for citing and cited papers is much shorter, namely, papers must be no more than two years old and cited within a current two-month time period. This means that papers must have received attention within a recent time frame. Papers are assigned to two-month periods and thresholds are set for each period and field to select 0.1% of papers, as shown in this table. The selection process compares the appropriate threshold against the citation count of the paper in the most recent two-month period.
View: Hot Papers Thresholds.
Updated: January 1, 2008

Also see "Essential Facts," for other information on how Essential Science Indicators works.