  We address the problem of detecting duplicate questions in forums, which is
an important step towards automating the process of answering new questions. As
finding and annotating such potential duplicates manually is very tedious and
costly, automatic methods based on machine learning are a viable alternative.
However, many forums do not have annotated data, i.e., questions labeled by
experts as duplicates, and thus a promising solution is to use domain
adaptation from another forum that has such annotations. Here we focus on
adversarial domain adaptation, deriving important findings about when it
performs well and what properties of the domains are important in this regard.
Our experiments with StackExchange data show an average improvement of 5.6%
over the best baseline across multiple pairs of domains.
