Studies have shown that the effects of scientific research on law and policy making are often fairly limited. Different reasons can be given for this: scientists are better at falsifying hypothesis than at predicting the future, the outcomes of academic research and empirical evidence can be inconclusive or even contradictory, the timing of the legislative cycle and the production of research show mismatches, there can be clashes between the political rationality and the economic or scientific rationality in the law making process et cetera. There is one ‘wicked’ methodological problem, though, that affects all regulatory policy making, namely: the ‘jump’ from empirical facts (e.g. there are too few organ donors in the Netherlands and the voluntary registration system is not working) to normative recommendations of what the law should regulate (e.g. we need to change the default rule so that everybody in principle becomes an organ donor unless one opts out). We are interested in how this translation process takes place and whether it could make a difference if the empirical research on which legislative drafts are build is more quantitative type of research or more qualitative. That is why we have selected two cases in which either type of research played a role during the drafting phase. We use the lens of the proportionality principle in order to see how empirical data and scientific evidence are used by legislative drafters to justify normative choices in the design of new laws.