Discordancy tests for outlier detection in multi-item questionnaires

W.P. Zijlstra, L.A. van der Ark, K. Sijtsma

Research output: Contribution to journalArticleScientificpeer-review

10 Citations (Scopus)


The sensitivity and the specificity of four outlier scores were studied for four different discordancy tests. The outlier scores were the Mahalanobis distance, a robust version of the Mahalanobis distance, and two measures tailored to discrete data, known as O+ and G+. The discordancy tests were Tukey’s fences (a.k.a. boxplot). Tukey’s fences with adjustment for skewness (adjusted boxplot), the generalized extreme studentized deviate (ESD), and the transformed ESD (ESD-T). Outlier scores O+ and G+ performed better than the Mahalanobis distance and its robust version. Discordancy tests ESD-T and adjusted boxplot were advocated for high specificity and ESD for high sensitivity.
Keywords: discordancy test, Mahalanobis distance, outlier detection in questionnaire data, outlier score O+, outlier score G+, robust Mahalanobis distance
Original languageEnglish
Pages (from-to)69-77
JournalMethodology: European Journal of Research Methods for the Behavioral and Social Sciences
Issue number2
Publication statusPublished - 2013


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