This thesis focuses on how it is possible to measure people’s knowledge on a topic where certain statements can effectively discriminate between knowledgeable and non knowledgeable people. It presents an application in measuring healthcare professionals’ knowledge about Sudden Infant Death Syndrome (SIDS) and its risk factors. Identifying the best and worst prepared healthcare professionals allows policymakers to reconsider the structure of their healthcare system and to implement targeted training initiatives about this topic. To do so, this research uses data belonging to the SIDS Project, a project meant to provide the first data about this topic in the United Kingdom and Spain. The mail survey referring to the United Kingdom was carried out in the South Central Strategic Health Authority in 2012, while the Spanish one was carried out in the provinces of Barcelona, Lérida and Tarragona in 2012 and 2013. The target population for the British survey consisted of general practitioners (GPs), while the target population for the Spanish survey consisted of paediatricians. Moreover, data about Italy were also available, which allowed cross country comparisons involving three different realities. This research shows that the Back-To-Sleep (BTS) message seems to have been effectively adopted by the British GPs, but, surprisingly, not as well received by the Spanish and Italian paediatricians. In the first case, in fact, more than 90% of the respondents recommended parents the supine position exclusively. In Spain and Italy, instead, this percentage was of 58% and 69% respectively. By contract, instead, the whole SIDS prevention message seems to have been better received in Spain and Italy than in the United Kingdom. British policymakers should reconsider the role of GPs in terms of delivering parents the BTS message, as they were found to be quite prepared. Spanish and Italian policymakers, instead, should try to increase the degree of adoption of the BTS message among their healthcare professionals. In particular, Spanish policymakers should urgently intervene in order to clarify that the supine position is the only one that can be deemed to be a protective factor against SIDS.