Over at MediaShift, Katie Donnelly and I explore this question in greater depth:
For public media makers, commercial measurements designed to track purchases or ad impressions aren't always enough to assess whether a media project contributes meaningfully to public life. Instead, assessing such projects' success depends first upon identifying the core stakeholders and intended outcomes, and using both qualitative and quantitative approaches to measure against related goals. Is it even possible to create a master metric? What are the differences and similarities in evaluating different kinds of projects? Let's take a look at four communities of practice within public media to see how they are tackling this thorny issue.