As reported in the journal Science, China has slightly edged out the United States in the number of most cited scientific papers, a key measure of research impact, according to Japan’s National Institute of Science and Technology Policy (NISTEP).

The milestone provides fresh evidence that China’s scholarship, known for its burgeoning quantity, is catching up in quality as well. Scholars disagree about the best methodology for measuring publications’ impact, however, and other metrics suggest the United States is still ahead—but barely.

NISTEP tallied the top 1% papers in terms of citations. Many such elite articles have authors from multiple countries, however, which complicates the analysis. In one study, NISTEP used a method called “fractional counting” to divide the credit. If, for example, one French and three Swedish institutions contributed to a paper, France received 25% of the credit and Sweden 75%.

Using that measure, China accounted for 27.2% of the most cited papers published in 2018, 2019, and 2020, and the United States for 24.9%. Next was the United Kingdom, with 5.5%; Japan was in 10^th place.

China’s rising production of top-cited papers is “remarkable,” NISTEP says; two decades ago it only ranked 13^th in the fractional counting metric.

In 2016, China passed the United States to become the world leader in the number of published papers, according to the report in Science. Critics have faulted the quality of Chinese research, but the new study shows China is getting better at doing the kind of top-notch science that gets cited by many researchers.

Other measures of impact still put the United States ahead.