Objective: A discourse analysis was conducted of peer-written blogs about the chronic illness endometriosis to understand how bloggers present information sources and make cases for and against the authority of those sources. Methods: Eleven blogs that were authored by endometriosis patients and focused exclusively or primarily on the authors' experiences with endometriosis were selected. After selecting segments in which the bloggers invoked forms of knowledge and sources of evidence, the text was discursively analyzed to reveal how bloggers establish and dispute the authority of the sources they invoke. Results: When discussing and refuting authority, the bloggers invoked many sources of evidence, including experiential, peer-provided, biomedical, and intuitive ones. Additionally, they made and disputed claims of cognitive authority via two interpretive repertoires: a concern about the role and interests of the pharmaceutical industry and an understanding of endometriosis as extremely idiosyncratic. Affective authority of information sources was also identified, which presented as social context, situational similarity, or aesthetic or spiritual factors. Conclusions: Endometriosis patients may find informational value in blogs, especially for affective support and epistemic experience. Traditional notions of authority might need to be revised for the online environment. Guidelines for evaluating the authority of consumer health information, informed by established readers' advisory practices, are suggested.
