The small reduction in the weighting that impact will carry in the first research excellence framework has been met by a mixed response from the academy.
The Higher Education Funding Council for England announced this week that a measure of the impact of research on the wider world will count for 20 per cent in the 2014 REF, not the 25 per cent initially envisaged. Output will count for 65 per cent and research environment for 15 per cent.
David Sweeney, director of research, innovation and skills at Hefce, said he still believed that 25 per cent was right "in principle" and envisaged it being adopted in subsequent REF exercises.
But he added that the reduced figure for the inaugural REF recognised the "developmental" nature of impact assessment while still being high enough to justify the effort that departments would need to put into their submissions. He said that it was "difficult to see" how the 15 per cent weighting previously called for by Million+ and the Russell Group would have done that.
Pam Tatlow, chief executive of Million+, which represents new universities, said she was happy with the 20 per cent weighting following last year's pilot impact assessment exercise, which had "demonstrated the formula that is being adopted is workable".
But Wendy Piatt, director general of the Russell Group of larger research-intensive universities, believes the figure should be "considerably lower". She said: "Giving such a high weighting to a new and untested assessment adds a further element of uncertainty and risk to a sector already subject to a period of considerable change and instability."
David Price, vice-provost for research at University College London, said he could "live with" 20 per cent, but regretted that environment was not equally weighted.
Meanwhile, the University and College Union accused David Willetts, the universities and science minister, of breaking a promise to listen to the concerns of the 18,000 academics who signed a petition in 2009 against the impact measure.
When he came into office, Mr Willetts delayed the REF by a year to consider these concerns.
"The funding councils will now roll out essentially the same untested proposals that were decisively rejected last year," said Sally Hunt, UCU general secretary.
Rachel Winzer, director of research at the 1994 Group of smaller research-intensive universities, said 20 per cent was a "sensible option" while also calling on Hefce to clarify the impact weighting in its funding formula.
But Philip Moriarty, professor of physics at the University of Nottingham, said he did not care whether the weighting was 15 or 20 per cent because the concept of attempting to assess research impact was "fundamentally flawed".
"Like many scientists, I don't do research to engage with users: I do research to address particular questions," he said.