TOKYO -- Japan ranks ninth worldwide as a producer of highly regarded scientific research, down from seventh in last year's edition of a survey.
The National Institute of Science and Technology Policy, affiliated with Japan's science and education ministry, released its updated ranking Tuesday based on global publication data spanning 2013 through 2015.
Japan ranks fourth in terms of total output, behind the U.S., China and Germany. But it slips to ninth when it comes to the share of the world's most-cited research papers -- the papers in the top 10% by citations. Last year's survey covered the 2012-14 period.
The U.S. was the top contributor, producing 28.5% of that elite work on average. China stood second with 15.4%, followed by the U.K. with 6.2%. Japan produced just 3.1% of highly cited research.
Japan spent the third most on research and development in 2015 -- 18.9 trillion yen ($171 billion) -- trailing only the U.S. at 51.2 trillion yen and China's 41.9 trillion yen.
Japan's decline in this survey's ranking appears linked to the nation's shrinking number of university researchers younger than 40, a group particularly likely to produce top-quality studies of the sort that take Nobel Prizes.
Nor does Japan contribute heavily to papers produced jointly with researchers elsewhere -- a sign that this country is quickly being left behind by the global scientific community.