Probabilistic Models for Text in Social Networks
Text in social networks is a common form of data. Common examples include emails between coworkers, text messages in a group chat, or comments on Facebook. There is value in developing models for such data. Examples of related services include archiving emails by topic and recommending job prospects for those seeking employment. However, due to privacy concerns, these data are relatively hard to obtain. We therefore work with similar data of the same structure which are publicly available to design and experiment. Motivated primarily by topic discovery, this thesis begins with a thorough survey of models which extend the foundational probabilistic topic model, latent Dirichlet allocation. My focus is on those which endow documents with meta data, like a time stamp, the author, or a set of links to other authors. Each approach is given common notation, described in terms of a structural innovation to LDA and presented in a graphical model. The review reveals, to our knowledge, there was previously no model which combines dynamic topic modeling and community detection. The first data set studied in this thesis is a corpus of political blog posts. Our motivation is to learn communities, guided by the presence of links and dynamic topic interests. This formulation enables new link recommendation. We therefore develop an appropriate Bayesian probabilistic model to learn these parameters jointly. Experiments reveal the model successfully identifies a group of blogs which discuss sensational crime, despite having very few links between these blogs. It also enables presentation of top blogs, according to various criteria, for a specified topic interest community. In a second analysis of the blog post data I develop a similar model. The motivation is to partition documents into groups. The groups are defined by shared topic interest proportions and shared linking patterns. Documents in the same group are reasonable recommendations to a reader. The model is designed to extend the foundational LDA. This enables easy comparison to a strong baseline. Also, it offers an alternative to LDA for situations where a hard clustering of documents is desired, and documents with similar enough topic proportions are clustered together. It simultaneously learns the linking tendency for each of these groups. We show a different application of a probabilistic model for text data in social networks to related text event sequence data. Here we analyze a transcription of group conversation data from the movie 12 Angry Men. A main contribution is an algorithm based on marked multivariate Hawkes processes to recover latent structure, learning the root source of an event. The algorithm is tested on synthetic data and a Reddit data set where structure is observed. The algorithm enables partial credit attribution, distributing the credit over likely people who start each new conversation thread. The above models and applications demonstrate the value of text network data. Generalized software for such data enables visualization and summarization of model outputs for text data in social networks.