Magazines that compile league tables have an interest in instability - playing around with their methodologies to ensure rankings remain newsworthy.

This was the argument made by Alice Gast, president of Lehigh University, Pennsylvania, at the Lord Dearing memorial conference at the University of Nottingham this month.

She has a point. Dramatic movements in the league tables make the news and generate interest - helpful for the circulation figures.

But too much movement raises questions about credibility: everyone knows that it takes more than 12 months for an 800-year-old university to lose its status, or for a young pretender to ascend the heights.

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³ÉÈËVRÊÓƵ serves a highly intelligent, engaged and critical expert community, so the credibility of our World University Rankings is far more important than any short-term noise they may generate. So why have we changed our rankings data provider and methodology, making further instability inevitable, at least between 2009 and 2010?

One of our key concerns with the old system was that even with a largely stable methodology, there was far too much variation from one year to the next.

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In 2009, the average shift in position among the top 200 was 14 places, and three institutions moved more than 70 places each.

So by ceasing to use our old methodology and data-collection system, we will create short-term instability, but this is less important to us than the long-term credibility of our rankings.

One of the key measures of success for the new rankings will be the international academy's faith in them, even if that means they become a little more boring for university marketing chiefs and the wider media.