Classification tends to parallel Bayesian hypothesis assessment, again treating type I and II errors symmetrically. For example, I might do a logit regression and classify cases with fitted P(I=1)<1/2 as group 0 and cases with fitted P(I=1)>1/2 as group 1. The classification threshold of 1/2 produces a ``Bayes classifier".

Bayes classifiers seem natural, and in many applications they are. But an interesting insight is that some classification problems may have hugely different costs of type I and II errors, in which case an NP classification approach may be entirely natural, not clumsy. (Consider, for example, deciding whether to convict someone of a crime that carries the death penalty. Many people would view the cost of a false declaration of "guilty" as much greater than the cost of a false "innocent".)

This leads to the idea and desirability of NP classifiers. The issue is how to bound the type I classification error probability at some small chosen value. Obviously it involves moving the classification threshold away from 1/2, but figuring out exactly what to do turns out to be a challenging problem. Xin Tong and co-authors have made good progress. Here are some of his papers (from his USC site):

- Chen, Y., Li, J.J., and
__Tong, X.__(2019) Neyman-Pearson criterion (NPC): a model selection criterion for asymmetric binary classification. arXiv:1903.05262.***** __Tong, X.__, Xia, L., Wang, J., and Feng, Y. (2018) Neyman-Pearson classification: parametrics and power enhancement.*arXiv*:1802.02557v3.- Xia, L., Zhao, R., Wu, Y., and
__Tong, X.__(2018) Intentional control of type I error over unconscious data distortion: a Neyman-Pearson approach to text classification.******arXiv*:1802.02558. __Tong, X.__, Feng, Y. and Li, J.J. (2018) Neyman-Pearson (NP) classification algorithms and NP receiver operating characteristics (NP-ROC).******Science Advances,*4(2):eaao1659.- Zhao, A., Feng, Y., Wang, L., and
__Tong, X.__(2016) Neyman-Pearson classification under high-dimensional settings.******Journal of Machine Learning Research,*17:1−39. - Li, J.J. and
__Tong, X.__(2016) Genomic applications of the Neyman-Pearson classification paradigm.*Chapter in Big Data Analytics in Genomics.*Springer (New York). DOI: 10.1007/978-3-319-41279-5; eBook ISBN: 978-3-319-41279-5. __Tong, X.__, Feng, Y. and Zhao, A. (2016) A survey on Neyman-Pearson classification and suggestions for future research.******Wiley Interdisciplinary Reviews: Computational Statistics*, 8:64-81.__Tong, X.__(2013). A plug-in approach to Neyman-Pearson classification.******Journal of Machine Learning Research*, 14:3011-3040.- Rigollet, P. and
__Tong, X.__(2011) Neyman-Pearson classification, convexity and stochastic constraints.*Journal of Machine Learning Research,*12:2825-2849.

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