RESEARCH FRONT METHODOLOGY
Research areas in science, particularly those at the cutting edge of
their fields, are characterized by patterns of intense communication
between scientists. This communication manifests itself in various
ways, both formally and informally, but prominent among these are
citations from one scientist’s work to another. Patterns of
citation reflect a fine-grained selection process of how scientists
build on each others’ work, and the relationship of these works
to one another. Such patterns can be used to create a picture of the
state of a specific research area in terms of the papers that
constitute its core of seminal work.
The procedure to accomplish this in
Essential Science IndicatorsSM from
Thomson Reuters is called Research Front
analysis. It is based on identifying the most-cited papers across
multiple disciplines over a five-year period, and then determining
how often these papers have been jointly cited—that is, how
often, in the footnotes or references of given papers, a citation to
one item is accompanied by a citation to another highly cited item.
This defines the frequency of co-citation of the two highly cited
Identifying research fronts involves manipulating the co-cited papers
in order to group together those that are strongly related. Before
embarking on this process, a threshold is set on the integer
co-citation frequencies to eliminate very low values, and the remaining
frequencies are converted to a normalized form using the following
Normalized co-citation = Integer co-citation frequency of A and
B/(citation frequency A*citation frequency B)^.5
In other words, we divide the co-citation frequency by the square root
of the product of the citation frequencies of the two papers. A second
threshold is set on these normalized values. In the most recent data
run for Essential Science Indicators, the integer threshold
was set to accept co-citation frequencies of 2 or greater, and the
normalized threshold was set at 0.1.
Starting with a co-cited pair that meets the thresholds, this grouping
procedure then finds other pairs that share common papers. The
gathering process continues until no other pairs of papers can be added
to the set. This process is commonly known as single-link clustering.
The resulting clusters vary in size from a minimum of two papers to
some maximum size.
The numeric attributes of fronts can help determine the significance of
the areas and their stage of development. The number of core papers in
the front and the total citations received give indications of the size
of the area. The numbers of citations per core paper give an indication
of the focus or concentration of effort. The average publication year
and distribution of core papers by year give an indication of currency
or "hotness"—that is, how quickly research is changing and
whether there are new developments. An analysis of frequently occurring
keywords or phrases in the titles of the paper, as given by the front
name, can give an indication of the subject content and thematic focus
of the area.
Research front analysis will not identify all research areas or all the
papers in an area. However, it can assist in identifying areas where
important work is being done and where the scientific community is
focusing its attention.
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