Nanyang Technological University, which has traditionally lagged behind the National University of Singapore in international rankings, has upset the apple cart and overtaken Singapore's oldest university this year.

In the Quacquarelli Symonds (QS) World University Rankings released this morning, NTU moved up two places to be ranked 11th, while NUS fell from the 12th to 15th position. Singapore Management University was placed in the 441-450 category.

NTU has made improvements across four of the six metrics that QS uses to rank universities and has made the biggest gains in employer reputation and citations per faculty.

QS said analysis of Scopus/Elsevier academic citations data shows that NUS has higher overall research output and citations impact.

But NTU scored higher because of how QS assesses research impact. Since 2015, QS has adjusted the research data numbers to offset the advantage that institutions with large volumes of medical research have.

Also, NTU has fewer faculty members - 4,300 as opposed to 5,100 at NUS - resulting in a higher citations-per-faculty score.

"This disparity is the primary driver of NTU's success this year," said QS, adding that NTU's ascendancy is also best understood as part of a recurrent global trend - "universities with a heavy technological focus have made consistent improvements and, in many cases, are gaining ground".

Mr Ben Sowter, research director at QS, said NUS and NTU appear to share a common comparative narrative with Harvard and the Massachusetts Institute of Technology. MIT overtook Harvard in the 2012 rankings.

"So perhaps it has only been a matter of time before NTU's parallel journey would carry them ahead of NUS, as it has this year," he said.

MIT held its No. 1 position for the sixth year running in the table which ranks the world's top 959 higher-education institutions this year. Stanford is second and Harvard, third.

Professor Bertil Andersson, president of NTU, noted that the university had risen from the 74th place in the 2010 QS ranking, and said: "As a university, we have been in hyper drive - ramping up research, designing innovative academic and research programmes, building new facilities and more." He said NTU's young and upcoming scientists make up 8 per cent of the faculty, but they account for almost 40 per cent of NTU's citations in top research journals.

"They represent the NTU of tomorrow," he said.

Mr Sowter said NTU's rise showed that young, well-run institutions could quickly achieve success.

He said NUS, which was ranked No. 1 in Asia for academic and employer reputation, "remains consistently excellent", but dropped a couple of places owing to the "ever-escalating standards" set by the world's leading universities.

NUS president Tan Chorh Chuan said: "NUS will continue to stay focused on bringing positive impact to the communities we serve through education and research."

He also commented on NUS' placing in another ranking released today - Asia's 75 most innovative universities - where NUS was placed 11th, the same as last year.

Prof Tan said it was recognition of the "deep impact" of NUS' research towards the advancement of science and technology.

NTU has climbed from its 35th position last year to be placed 25th this year in the list by Reuters.