Despite Slide in World Share, U.S.
Impact Still Looks Strong
by Christopher King
The United States continues to see its share of world science erode,
particularly in the face of a steady rise by the collective nations of the
Asia Pacific region, but the citation impact of U.S. scientific papers
still surpasses the world average by a healthy margin in the major fields
of science, according to a new Science Watch survey.
Science Watch has been monitoring this trend for a dozen years
now, most recently in
July/August of 2005. On that occasion, as in the
graph to the right, the U.S. percent share of world science was
tracked against that of the Asia Pacific bloc and the nations making
up the European Union. The current graph adds another three years of
data to the last survey, reflecting figures through 2007.
For this study, as with the previous installments, Science
Watch turned to the
Thomson Reuter'sNational Science Indicators, a database
containing publication and citation statistics for more than 100
subfields of science and the social sciences. In addition to
covering upwards of 170 individual countries, the database contains
aggregate figures for the Asia Pacific region, the European Union,
and the collective nations of Latin America (a region not included
in the present graph).
In the 2005 report, which covered year-by-year world share through
2004, the graph showed the U.S. percentage sliding gradually while the
Asia Pacific share rose steadily. The current graph finds these trends
continuing, with the two geographic entities now close to convergence
on their present paths. The Asia Pacific percentage has increased
apace: 25.9% in 2005, 27.2% in 2006, and 28.2% in 2007. The U.S. share,
meanwhile, has ticked downward, from 32.8% in 2005 to 32.4% in 2006 to
31.5% in 2007. And the European Union is also trending downward: after
a considerable stretch in the 39%-share range in the late 1990s, the EU
was at 38.0% in 2005, 37.6% in 2006, and 37.3% in 2007.
Undoubtedly, an increasing scientific output by the nations of Asia,
along with an ever-growing degree of international collaboration and
coauthorhip on scholarly papers, account significantly for the Asia
Pacific group exhibiting a greater presence in world science and
appropriating a greater percentage of world share. (See, for example,
the recent survey of China's science surge, Science Watch,
2008.) So it's not necessarily a story of U.S. decline. But one
trend bears watching: in the last two years, the absolute number of
Clarivate-indexed scientific papers from the U.S. has edged
downward: from a high of roughly 291,500 in 2005 to approximately
286,000 in both 2006 and 2007.
Meanwhile, by the measure of citation impact, U.S. science still
appears quite healthy. Table 1 below shows U.S.
world share and citation impact in 21 main fields of science, ranked
according to those fields in which U.S. "relative impact" is strongest
compared to the world average over a recent five-year period.
Topping the list is Physics, in which the U.S. impact mark of 6.15
cites per paper surpassed the world mark of 3.96 cites by 55%. In all
the fields shown, and particularly in the physical-sciences fields atop
the list, U.S. impact registers well above the world mark.
For another snapshot of current U.S. science, Science Watch
turned to Clarivate' unique store of
Research Fronts. These emerging areas of
research are identified by a foundational "core" of previous papers
that are frequently cited together by a group of more-recent
Table 2 below offers a sampling of eight
Research Fronts that each feature comparatively recent core literature
and, more important, a predominance of U.S.-based institutions listed
among the collective author addresses for each grouping of core papers.
Thus, the list constitutes a small selection of U.S. concentration in
Atop the list, with its core papers showing more than an 87%
preponderance of U.S. addresses, is a Research Front involving a
related array of topics centering on genome-wide mapping of chromatin
state in the cell, on factors initiating and controlling transcription,
and on the regulation of embryonic
stem cells, along with other aspects of cellular
differentiation. One of the core papers for this front (T.
Mikkelsen, et al., "Genome-wide maps of chromatin state in
pluripotent and lineage-committed cells," Nature,
448: 553-60, 2007) has been sufficiently cited to figure in a
recent Biology Top Ten and was discussed by Biology correspondent
Jeremy Cherfas in the
Another recent U.S.-centric Research Front deals with processes for
creating zirconium diboride and silicon carbide
ceramics—materials suited for hypersonic flight and other
applications involving exposure to extremely high temperatures.
Third on the list, also with more than 80% representation of U.S.
institutions, is a Research Front examining phase 0 trials in cancer
therapy. The phase 0 trial, a relatively recent designation, typically
involves a small number of patients given microdoses of a compound in
order to evaluate its basic biochemical efficacy before proceeding to
phase I and subsequent trials. The papers in this core discuss the
practicalities—not to mention the ethics—of phase 0 trials
in the development of anti-cancer agents.
Elsewhere on the list, separate Fronts involving
quantum dots, and
ultraviolet surveys of the heavens exemplify what appears to be
currently healthy U.S. research in the physical
Christopher King is the Editor of the Science
Watch® Newsletter, Clarivate.
Research fronts are clusters of highly cited papers, and research front
maps are diagrammatic representations of the co-citation links among
the highly cited papers that comprise the cluster. In addition, some
Special Topics have associated maps that are selected from the current
Research Front set that are relevant to the featured special topic.
View a list of all
Front Maps within ScienceWatch.com.
Keywords: U.S. research, scientific output, world share of science,
Asia Pacific, U.S. impact, U.S. world share.