An enquiry into scientific and media discourse in the MMR controversy: authority and factuality.

In this paper, we investigate two scientific articles at opposite ends of the MMR debate-Wakefield et al. (1998) (which started the debate) and Taylor et al. (1999)-and four media articles published to inform the public of the results of these two scientific studies. Because people need to assess truth claims about health risks, communicators seek to establish their believability in two ways: authority (i.e., the attribution of scientific claims to sources that may be perceived as believable because of their status) and factuality (i.e., the moderating, limiting, or highlighting of truth claims). The importance of authority was confirmed by the media texts' preference for direct quotes and messages about what people ought to do, especially at the beginning of the debate. Our most significant find, however, relates to two important indicators of factuality: avoidance of vague references and high use of epistemic modals, where Wakefield et al. displays a pattern not at all different from the media texts and opposite to that expected from a scientific text. That Wakefield et al. stands out in the majority of indicators investigated is of interest in view of its controversial position in the MMR debate and worthy of further study.