It has become one of the most talked-about books of the moment, but recent attacks from political groups have led its authors to say that they will no longer respond to any criticism that is not peer-reviewed.
The Spirit Level by Richard Wilkinson, emeritus professor of social epidemiology at the University of Nottingham, and Kate Pickett, professor in the department of health sciences at the University of York, was published in March 2009.
Despite its huge popularity, the book's argument - that inequality exacerbates a string of social problems - has been attacked recently in three non-peer-reviewed reports, including one for the right-wing think tank Policy Exchange.
The authors posted detailed responses on their Equality Trust website, but announced that in future, they would respond only to criticism in peer-reviewed journals "in order to distinguish between well-founded criticism and unsubstantiated claims made for political purposes".
Their stance was attacked by journalist Brendan O'Neill, editor of the Spiked blog, who called the move "snooty".
Professor Wilkinson agreed that the move grated with the book's egalitarian ethos, but said it reflected the authors' "near-total exhaustion" due to all the demands on their time, such as answering a "deluge" of emails, writing articles and giving lectures all over the world, as well as keeping up their ongoing research.
"We've done about 300 lectures since the book came out. Kate has a full-time job and I do interviews almost every day," Professor Wilkinson said.
"Instead of appealing to peer review, we would ideally have had research teams and an institute of staff to work with us. But we have absolutely no administrative support and have entirely lost our free time."
He insisted that recent attacks had been poorly researched and were intended merely to cast doubt on The Spirit Level's arguments in the public's mind.
"We saw it with smoking and climate change: it is always possible to sow doubt by ignoring the evidence and knowing that your readership will be none the wiser. Already political groups are citing these criticisms as if they were valid," he said.
"In other fields, people would know their thoughts were of limited value if they were not specialists: I would not dream of telling an engineer, surgeon or pilot how to do their job."
Professor Wilkinson expressed doubts about the suggestion that research funders should consider offering financial support to help academics rebut high-profile, politically motivated attacks, but agreed there was an issue about protecting the "benefits of expensive research".
"These politically motivated attacks undermine science and the process that the research councils encourage of disseminating the findings of research," he said.
But Mr O'Neill disputed the idea that peer-reviewed work was politically neutral.
"One might argue that their critics are at least being honest in presenting clearly polemical attacks, whereas Professor Wilkinson and Professor Pickett are rather disingenuously presenting their political agenda as purely evidence-based," he said.
Last month, Professor Wilkinson admitted at the Economic and Social Research Council's Research Methods Festival that pure objectivity was impossible.
"Scientists need a hard core to their theory that they won't allow to be refuted," he said.