The 5 Cs of Engagement
The strongest form of engagement is demonstrated by using an item as inspiration to create your own, for example, writing your own blog post that responds to or refutes someone else's blog post. Creation requires the most thought and investment of time, actively generates conversation, and therefore indicates the highest level of engagement.
Reading a blog post and then leaving a comment requires an investment of time, thought and effort (or sometimes just typing and name-calling...), and is a form of conversation. However, it requires less effort than writing a whole blog post. So while it is an important action, it does not indicate as much engagement as Creating.
Sharing and discussing information can often be started with one click, so it doesn't require a major investment of effort. However, a desire to share is a strong indication of relevance, and the act of sharing and its ensuing discussion are acts of conversation. Use of social media applications like Twitter encourage both the sharing of information and the resulting conversations. As a result, social media "chatting" indicates a good level of engagement.
Bookmarking or submitting items to social sites also tend to be "one-click" actions. They are intentional acts of archiving and sharing, but don't require much time or effort. However, the sharing that occurs often sparks conversations, so Collecting does demonstrate some engagement.
Activities like clicks and page views indicate lower engagement because they're passive interactions. Clicking a link to read a blog post doesn't require much work, and you're not giving anything back except your reading time. It is an intentional act, however, and thus indicates a mild level of interest and engagement. Which may grow after the item is read.