One of the issues with any forum, be that a blog or some other means of collaborative writing is how to interpret apparent disengagement.
As an example, Ecademy is a social networking site, which maintains a number of clubs (groups) each with their own forum and also has some general areas for blogging type activity.
I lead a number of groups on Ecademy, including BlackStar, the life members club and a group called The Debating Society. In all of these clubs only 1 in 10 members participate, but the research shows that this is typical. One issue that arises is when there are polarised discussions. Often a lone voice arguing against a few vocal people appears to be in a significant minority when the reality is far harder to judge.
Silent people are not truly silent, because they leave trails of data behind them when they view a page. If you capture this data then you know the page has been viewed and if you capture arrival time and leaving time you could even surmise if it has been read.
Is silence agreement? - does the failure to post mean that you agree with the previous post? - of course not.
From a societal web point of view there's a danger of others misinterpreting a lack of comment as a lack of engagement. Societies work as well for those that speak up as those that don't, but we haven't yet got that clarity on-line.


