Mixtures of Hierarchical Topics with Pachinko Allo cation
Jun 23, 2007 9870 views 
The four-level pachinko al location model (PAM) (Li & McCallum, 2006) represents correlations among topics using a DAG structure. It does not, however, represent a nested hierarchy of topics, with some topical word distributions representing the vocabulary that is shared among several more specific topics. This paper presents hierarchical PAM -- an enhancement that explicitly represents a topic hierarchy. This model can be seen as combining the advantages of hLD's topical hierarchy representation with PAM's ability to mix multiple leaves of the topic hierarchy. Experimental results show improvements in likelihood of held-out documents, as well as mutual information between automatically-discovered topics and humangenerated categories such as journals.