The the latest issue of First Monday has an interesting study by Bernardo Huberman and other researchers at HP's Social Computing Lab on Social Networks that Matter: Twitter Under the Microscope. Among other things, it reveals a hidden network of relationships underpins those declared in our use of Twitter:
In conclusion, even when using a very weak definition of “friend” (i.e., anyone who a user has directed a post to at least twice) we find that Twitter users have a very small number of friends compared to the number of followers and followees they declare. This implies the existence of two different networks: a very dense one made up of followers and followees, and a sparser and simpler network of actual friends. The latter proves to be a more influential network in driving Twitter usage since users with many actual friends tend to post more updates than users with few actual friends. On the other hand, users with many followers or followees post updates more infrequently than those with few followers or followees.
In JP Rangaswami's read of the study, he is holding on to a hunch.
I’ve tended to believe that if anything, social software would help raise the Dunbar number. The studies above suggest this is not the case. But I’m still holding on to my hunch.
Why? Because I think we live in an age where there something wonderful happening, something that just has to affect the Dunbar number, something that is accentuated by social software.
Something wonderful is happening, but it is augmentation, not accentuation. The Dunbar limit of 150 is the number of people and how they are related to each other at a moment in time. It is a cognitive constraint, a ceiling that can't be broken (perhaps until neurotechnology messes with our wetware).
What Social Software can do for your Dunbar number is help what goes in and out of the 150. Help you discover people you should add to your network. Stay in touch with old friends so they can be active friends for at least a moment in time. Help others sift out of view. Your Dunbar number is made up of both strong and weak ties that happen to all be related somehow to you for a moment in time. Social Software has even more potential to help refresh your cache of 150 for a moment in time to serve your changing needs.