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Tuberculosis (Edinb). 2017 May;104:20-23. doi: 10.1016/ Epub 2017 Feb 16.

Revisiting the Hunter Gaston discriminatory index: Note of caution and courses of change.

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Laboratory of Molecular Epidemiology and Evolutionary Genetics (former Laboratory of Molecular Microbiology), St. Petersburg Pasteur Institute, 14 Mira Street, St. Petersburg 197101, Russia. Electronic address:


Hunter Gaston Discriminatory Index (HGDI) is a widely used estimator of discriminatory power of genotyping methods and diversity of molecular markers in bacterial pathogens, including Mycobacterium tuberculosis. In my opinion, the index is somewhat misleading: a closer look at common practice and particular studies reveals that values in the range of 0.6-0.9 are modest but uncritically perceived as high. I propose and discuss three courses of change: (i) to continue using HGDI but be aware of the true meaning behind its value and increase a threshold of acceptable resolution to the more adequate values of 0.90-0.99, depending on study design; (ii) to turn to other known indices of diversity (e.g., Shannon index), in order to complement HGDI; (iii) to develop new, intuitively more realistic estimator.


Discriminatory power; Hunter Gaston index; Molecular typing; Shannon-Wiener index; Spoligotyping; VNTR

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