Can Quantcast measure Ajax activity?

Yes. Our tag ultimately measures the number of times a browser loads Ajax, whether the load was triggered by a user or by an Ajax call. This is represented as “impressions” or “events” in our reports.

For sites that make heavy use of Ajax, there are considerations to be made in interpreting this number: It can understate user engagement if the site updates much of its content through Ajax without reloading our tag, or it can overstate engagement if the site reloads our tag when the user session is inactive.