Sometimes I feel like a broken record because I keep pointing you back to some of the same sources time and again. Today, more of the same.
First Monday is a peer-reviewed online journal the covers some important topics for those of us who try to make a living from this internet media stuff and today's edition includes a very important article regarding how we might want to think about measuring social media. Observe:
Online social network (OSN) research to date has been dominated by a tendency to abstract a given OSN as a static graph. The appeal of modeling all OSNs uniformly with nodes to represent generic users and links to connect those that are “acquaintances” (covering a range of meanings from real–world friendship to mere interest in their comments and links) is understandable. However, not all OSNs are equal — indeed, not all networks studied under the guise of OSNs are truly “social networks” — and ignoring the full array of features of real–world OSNs is detrimental to understanding these systems.
The allure of a “one size fits all” model is that it brings the study of OSNs squarely into the realm of graph theory, with ready access to a rich set of available techniques and models. It also makes OSNs a prime application for the popular new field of network science, which encourages comparisons of networks from very different domains via well–known metrics such as node degree distribution, clustering coefficient, network diameter, etc. Observed similarities in these metrics across different networks are used to argue for the existence of universal features of networks. [more]
Please take a look. This is good stuff.

