Around the globe, ex ante evaluation of legislation has become an established rationalisation of legislative processes. Legislators, politicians, and the public at large increasingly demand new laws to have a particular effect and no unwanted side effects. Various instruments are being applied that all have in common that they must predict the effect of new legislation. Until now, most publications on regulatory impact assessment praise such instruments as being extremely useful. Scepticism, however, is in order as well. Is it not as difficult to predict the future effect of a new set of...