This document discusses methods for discovering emerging topics in social streams using two approaches: NADS (Notice-Abnormality based Discovery of Subjects) and VFDT (Very Fast Decision Trees). It proposes a probability model that captures both the normal posting behavior of users as well as the frequency of users being mentioned in posts. This model is used to quantitatively measure the novelty and potential impact of a post based on user commenting behavior. The approaches can identify new topics as early or earlier than text-frequency based approaches, especially when topics are poorly represented by post texts alone. The document provides details on implementing the probability model, calculating text frequency scores, deriving anomaly scores, using change point detection to recognize emerging topics, and