Absence time and user engagement: evaluating ranking functions

In the online industry, user engagement is measured with various engagement metrics used to assess users' depth of engagement with a website. Widely-used metrics include clickthrough rates, page views and dwell time. Relying solely on these metrics can lead to contradictory if not erroneous conclusions regarding user engagement. In this paper, we propose the time between two user visits, or the absence time, to measure user engagement. Our assumption is that if users find a website interesting, engaging or useful, they will return to it sooner -a reflection of their engagement with the site -than if this is not the case. This assumption has the advantage of being simple and intuitive and applicable to a large number of settings. As a case study, we use a community Q&A website, and compare the behaviour of users exposed to six functions used to rank past answers, both in terms of traditional metrics and absence time. We use Survival Analysis to show the relation between absence time and other engagement metrics. We demonstrate that the absence time leads to coherent, interpretable results and helps to better understand other metrics commonly used to evaluate user engagement in search.