Outlier detection in contingency tables based on minimal patterns
Anew technique for the detection of outliers in contingency tables is introduced, where outliers are unusual cell counts with respect to classical loglinear Poisson models. Subsets of cell counts called minimal patterns are defined, corresponding to non-singular design matrices and leading to potentially uncontaminated maximum-likelihood estimates of the model parameters and thereby the expected cell counts. Acriterion to easily produce minimal patterns in the two-way case under independence is derived, based on the analysis of the positions of the chosen cells. Asimulation study and a couple of real-data examples are presented to illustrate the performance of the newly developed outlier identification algorithm, and to compare it with other existing methods.
outliers contingency tables minimal patterns robustness loglinear models