As Table 1 demonstrates, the percentage of USA authors in each
5-year time block ranges from 52.4 to 87.5 from 1965 through
1994. Beginning in 1995 and continuing through 2014, however,
the percentage of USA authors drops systematically, from 46.4 to
12.7, while the number of non-USA authors rises from 46.4 to more
than 60 percent through 2014. Note also the rise of combinations of
USA and non-USA authors through 2014, indicating more
international collaboration. With respect to the continent of
authorship, detailed counts are available from the authors, but it is
fair to say that prior to 2000, almost all authors were from North
America or Europe, with only 12 articles published by Asian
authors, and only two by Australian authors. Since 2000, however,
the percentage of non-North American authorship has increased
sharply, with almost one-third of all published articles now
reflecting combinations of authors from continents other than
North America.