Stephen J. Dubner, Steven D. Levitt (2010). “Superfreakonomics: Global Cooling, Patriotic Prostitutes and Why Suicide Bombers Should Buy Life Insurance”, p.77, Penguin UK
Winston Churchill's addree as Home Secretary to Prime Minister Asquith on compulsory sterilization of 'the feeble-minded and insane', as quoted in "'Race', Sport and British Society" edited by Ben Carrington and Ian Mcdonald, 2001.