Global university rankings are now the subject of incessant debate on the international conference circuit. They have also spawned a host of national and institutional discussions. Over one weekend in May, they were being debated in Estonia, Germany and Korea; and with more meetings planned in the next few months in Mexico, Scotland and Switzerland, there is no sign of interest waning. This year's World University Rankings, published today, will no doubt fuel the debate, particularly given the level of flux in the main table.
Critics of the rankings will argue that turbulence confirms the unreliability of such exercises - the world's great universities do not alter substantially year by year. And indeed, the highest places have remained relatively stable over the three editions of our rankings. Harvard University has been top throughout, and nine of the top ten have maintained positions in that leading group. It is farther down the table that bigger swings take place, partly because of a change this year to a shorter period for the measurement of citations, but also because academics' views of the top universities in their subject do alter.
Rankings that place more weight on the past achievements of universities will display the stability that the critics crave: there are only six Nobel prizes, after all. But our rankings aim to give the most up-to-date picture possible of universities, seen through the eyes of the experts as well as through the limited statistical evidence that is internationally comparable. Below the established leaders, that inevitably results in some movement: opinions will vary on the relative standing of universities that are generally considered similar in quality.
Even at the very top, reputation is not set in stone. Harvard remains supreme, but a year of highly publicised internal wrangling and criticism from some well-respected figures has coincided with a narrowing of its lead over its nearest rivals. It will be interesting to see whether that is a temporary phenomenon, eclipsed perhaps by a period of calm and the appointment of a new president, or whether the damage is more long-lasting. Whichever is the case, it would be idle to pretend that controversy on such a scale has no impact on the standing of even the greatest university.
Our rankings - and others that have begun to spring up - will take time to develop fully. Further changes in methodology will be adopted as more sources of data become available and as a result of discussion with the academic community. Higher education is now so international, particularly where the leading research universities are concerned, that comparisons are both inevitable and essential. The challenge is to keep improving them.