Two university rankings were released yesterday.

One was the more closely watched list - the annual World University Rankings compiled by London-based education consultancy Quacquarelli Symonds. The other was Asia's 75 most innovative universities list, launched by Reuters last year.

Singapore's two leading universities - the National University of Singapore (NUS) and Nanyang Technological University (NTU) - fared well, but the big news with the QS ranking was NTU getting ahead of NUS for the first time. NTU was placed 11th this year, up two places, while NUS fell three places to be ranked 15th.

In the Reuters list, though, NUS was ahead - it was placed 11th, the same as last year. NTU had moved up 10 places to the 25th position. Soon, more rankings will follow, including the lists drawn up by Times Higher Education Magazine, the competitor to QS.

Increasingly, students and parents are using the tables to select universities, as are academics when deciding on positions. But students and parents should be reminded of the limitations of rankings.

As academics themselves have pointed out, the rankings are based on "bad social science", in using a mix of subjective and objective data. By choosing a particular set of indicators, such as how other academics rate a university, rankers decide what matters in higher education.

Some aspects, such as teaching quality, are assessed using proxy measures such as the ratio of academic staff to students and the number of staff with PhDs. Other qualitative aspects - such as innovative learning approaches and programmes that give students global exposure or nurture the entrepreneurial spirit - are hard to measure and hence not taken into account. But it is these intangibles that will make a difference to a student's learning and, further on, his or her job prospects.

With rising tuition fees and graduates in many economies facing job woes, it is important to rank the rankings and question if they are a true measure of the worth of universities.