Abstract
We present a discussion of Hubert et al. (2015)—hereafter, HRS15—that splits into two parts. In the first one, we argue that some structural properties of depth may, in some cases, limit its relevance for outlier detection. We also propose an alternative to bagdistances, which, while still based on depth, does not suffer from the same limitations. In the second part of the discussion, we investigate the possible uses of the weight functions that may enter the various integral functionals considered in HRS15.
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Notes
A few, isolated, small bagdistances arguably also may be a sign of “outlyingness”.
This is not only the case for shift outliers, but also for shape outliers, provided that the multivariate functional data considered contains derivatives of the original curves.
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Davy Paindaveine’s research is supported by an A.R.C. contract from the Communauté Française de Belgique and by the IAP research network Grant Nr. P7/06 of the Belgian government (Belgian Science Policy). Germain Van Bever’s research is supported by the British EPSRC grant EP/L010419/1.
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Paindaveine, D., Van Bever, G. Discussion of “Multivariate Functional Outlier Detection”, by Mia Hubert, Peter Rousseeuw and Pieter Segaert. Stat Methods Appl 24, 223–231 (2015). https://doi.org/10.1007/s10260-015-0307-x
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DOI: https://doi.org/10.1007/s10260-015-0307-x