Measuring Quality of User Interaction with Third Party Content

An online services system provides monitoring of user interaction with third-party content. The monitoring is performed by a script in a web page provided by the online services system, which script provides a timer invoked when the browser leaves the online services system's page for a page comprising third party content. When the online services system serves the page, the browser reads the HTML to render the page, including the script with the timer. When the user leaves the online services system page, the timer begins, and when the browser returns to a page provided by the online services system, the timer ends and duration information from the timer is provided to the online services system. Applications include measurement of the quality of interaction between users and a third party advertisers, in which time spent viewing third party content is a proxy for the quality of the interaction.