Was reading Occam’s Razor today, specifically Measuring Online Engagement: What Role Does Web Analytics Play? and Avanish says pretty much, that Web Analytics can't really tell you, without other measures, how engaged your visitors are in the generally accepted way most marketers view engagement; he distinguishes between kind of engagement and degree of it:
"…This means that both the lowest (apathy) and the highest degree of engagement need to be defined. The easiest way to do this is to define the average degree of engagement (the average score for several metrics of your choice across your site or based on a competitor-specific or industry-wide benchmark), considering everything that falls short of it as (increasing degrees of) apathy and everything beyond it as (increasing degrees of) engagement. In this way a customer’s degree of engagement assumes a non-relative meaning (it remains of course relative to your website’s, competitor’s or industry’s historical performance)."
"…
- Kind: Customers can be positively or negatively engaged with a company/product.
A more in-depth examination of kind would reveal its content, usually a mixture of emotional states and rational beliefs, such as, in the case of positive engagement, sympathy, trust, pride, etc
- Degree: The degree of positive or negative engagement lies on a continuum that ranges from low involvement, namely, the psychological state of apathy, to high.
An engaged person is someone with an above average involvement with his or her object of relatedness."
The way I'm reading his post, you can come up with a synthesis of metrics that might equate to degree of engagement but not type (positive or negative).
