One way to make this monitoring more accurate is to install a program on client devices which monitors what a user is doing. Comcast were doing this some years ago (and perhaps still are?), but got into big trouble when they got found out for performing man in the middle on HTTPS sessions so to analyse that data too – which of course would give them access to financial data, password etc. It looks like Compete use a similar client-based tracker, but I can't speak for the HTTPS stuff. So, you walk a fine line between accuracy and privacy of statistical data like this.

Not to mention the fact that since your data comes from people who willing (or unwittingly) installed spyware on their own system, you've got a demographic bias from the get-go.