The graphical model and generative story for ATAM.

<p>The graphical model representation of ATAM using plate notation, followed by the “generative story” description of the model. In the graphical model, the variable <i>z</i> denotes the topic index, and the Bernoulli variables <i>x</i> and <i>ℓ</i> are switch variables indicating whether a word is an ailment or topic word and whether a word is background noise. These three variables do not appear in the conditional likelihood because they have been summed out. <i>A</i> is the number of ailments, <i>Y</i> is the number of aspects, <i>Z</i> is the number of topics, <i>D</i> is the number of documents, and <i>N_m</i> is the number of tokens in document <i>m</i>. In the generative description, “Dir” refers to the Dirichlet distribution.