I see credible communication as a social benefit. Sandra Stewart, a colleague over at Thinkshift Communications, shared a beta "Credibility Quotient" to help quantify the credibility of initiatives. I found it useful as I thought about building nonprofit websites, and the kinds of messaging and communications strategies that become implicit in the architecture of the sites I build.
Thinkshift identifies several factors in determining credibility, including provable claims, accurate data, attention to challenges, relevance to the audience, consistency with actions and more. These factors and definitions show the different perspectives we can take when considering whether web content is credible, and helps to determine where to focus to fix any problems. For me, the details of the scoring and weighting are less important than the exercise in understanding what credibility factors are most important, and how to read content for these factors.