There is another barrier to evidence-based policy - just because the evidence is there does not compel anyone to use it. School driving lessons, Scared Straight programmes and many other policies continue despite solid evidence that they do not work. "What's not there is the automatic transfer of knowledge to practice," says Sherman. He points out that we have known since the 1850s that doctors can save lives by washing their hands more, yet in intensive care units the failure of doctors to wash their hands is still a major cause of death.
"Why would we expect elected officials to immediately change policy based on randomised trial research if we can't get doctors to wash their hands?" Sherman believes that policy documents, and journalists, should be clearer about the quality of evidence for new policies to help the good ones make their mark.