Outlier detection in contingency tables using decomposable graphical models

For high‐dimensional data, it is a tedious task to determine anomalies such as outliers. We present a novel outlier detection method for high‐dimensional contingency tables. We use the class of decomposable graphical models to model the relationship among the variables of interest, which can be depicted by an undirected graph called theinteraction graph. Given an interaction graph, we derive a closed‐form expression of the likelihood ratio test (LRT) statistic and an exact distribution for efficient simulation of the test statistic. An observation is declared an outlier if it deviates significantly from the approximated distribution of the test statistic under the null hypothesis. We demonstrate the use of the LRT outlier detection framework on genetic data modeled by Chow–Liu trees.