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Generally, papers reach their citation peak two, three, or even four years after publication. However, a small group of papers is recognized very soon after publication, reflected by rapid and significant numbers of citations. These papers are often key papers in their fields. We use a special filter to detect such "hot" papers. This involves looking at recently published papers and unusual citation activity in a current time period. We also take into account the varying citation rates across fields.

What are Hot Papers?

Hot Papers are papers that receive citations soon after publication, relative to other papers of the same field and age.

Time period for counts:

We measure age for hot papers in two-month periods rather than years, and we scan only those papers published in the last two years to see if they are receiving more citations than the norm. To get a very current sampling of citations, we count citations from only the most recent two-month period. The time periods are defined by Thomson Scientific database processing dates (the actual date when items are entered into the Thomson Scientific database, which is not necessarily the publication date). Note that the data is updated bimonthly (six times a year).

Field and age variations:

To correct for field variations in citation rate, each field is treated separately. Furthermore, since older papers tend to be cited more than newer (just published) papers, a separate analysis is made for each two-month grouping of papers, giving a total of 12 groupings over the two-year period.

Selection criteria:

A paper is selected as a Hot Paper if it meets a citation-frequency threshold determined for its field and bimonthly group. Citation-frequency distributions are compiled for each field and cohort. Thresholds are set by finding the closest citation count that would select the top fraction of papers in each field and period. The fraction is set to retrieve about 0.01% of papers. More information about the actual thresholds used in Essential Science Indicators.

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.