We have had to make some extraordinarily difficult decisions this week - on which institutions to exclude from our 2010 World University Rankings.

In the autumn, we will publish our annual list of the top 200 universities in the world, but it will be under an entirely new ranking methodology.

We are committed to publishing robust results that stand up to close scrutiny. A key principle of the rankings this year is that they are compiled in a spirit of open cooperation with institutions.

So the first principle - in contrast to some other systems - is that we rank only the universities that have actively submitted and signed off their key data.

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Those universities that have not provided data are not included.

We have also decided, after consultation with our platform group of almost 50 institution heads and experts, to exclude graduate schools.

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The feeling was that they are too much of a breed apart. Often small and highly specialist, with great research strength in a single area, their profiles do not fit well with the broad range of indicators we are using to build the tables.

Separate tables for graduate schools are a future option.

The 2010 tables will give heavy weighting to research paper citations indexed by Thomson Reuters - a widely accepted and strong proxy for research excellence.

But to ensure rigorous results, we have decided to exclude institutions that published fewer than 50 papers in 2008 - the final year of the rolling five-year period for which we collected citations data (as we judged that 2009 papers have not had enough time to accumulate citations).

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Such decisions will always be controversial, but we must take a clear editorial line in the interests of rigour and true comparability.

Phil Baty is editor, Times ÖйúAƬ World University Rankings. phil.baty@tsleducation.com

For the latest World University Rankings news, debate and social networking, see www.timeshighereducation.co.uk/worlduniversityrankings2010.