Answer Similarity Analysis at the Group Level

Answer similarity indices were developed to detect pairs of test takers who may have worked together on an exam or instances in which one test taker copied from another. For any pair of test takers, an answer similarity index can be used to estimate the probability that the pair would exhibit the observed response similarity or a greater degree of similarity under the assumption that the test takers worked independently. To identify groups of test takers with unusually similar response patterns, Wollack and Maynes suggested conducting cluster analysis using probabilities obtained from an answer similarity index as measures of distance. However, interpretation of results at the cluster level can be challenging because the method is sensitive to the choice of clustering procedure and only enables probabilistic statements about pairwise relationships. This article addresses these challenges by presenting a statistical test that can be applied to clusters of examinees rather than pairs. The method is illustrated with both simulated and real data.