Professor Sir Muir Gray, in his book Evidence-based Healthcare1 tells the old joke about the epidemiologist up in court on a serious charge. “How do you plead? Guilty or not guilty?” asks the judge. “I don’t know: I haven’t heard the evidence yet.”

Recent events bring comedy, evidence, and law together as Ricky Gervais, Richard Dawkins, and Sir Iain Chalmers join together in a campaign that weds scientific rigour to free expression. On Wednesday of this week, leading academics, publishers, journalists, performers, clinicians, and scientists issued a public statement2 backing science writer Simon Singh in his application to appeal against a libel judgment in the High Court. They fear that this judgment—if upheld—would have major implications for the ability of scientists, researchers, and other commentators freely to engage in robust criticism of scientific, and indeed purportedly scientific, work.

Singh, well-known for his books on Fermat’s last theorem and the big bang, wrote an article on 19 April 2008 in the Guardian newspaper criticising claims made by chiropractors about the efficacy of spinal manipulation in dealing with childhood conditions such as asthma, colic, and ear infections, among others. He suggested there was “not …