Abstract
The classical extremal index is an important characteristic of the asymptotic behavior of maxima in stationary random sequences. However, in practice it is also necessary to study maxima on more complex structures than the set of natural numbers. This paper continues the cycle of work devoted to the author’s generalization of the extremal index to a scheme of random-length series. This generalization allows working with a wider class of stochastic structures. For cases where there is no exact extremal index, partial indices were introduced earlier. Unlike the classical extremal index, they can take values greater than one (which corresponds to a negative dependence of random variables). The question whether the exact extremal index greater than one can exist remains open. In the paper, this question is partially closed (the impossibility is proved under certain conditions).
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Notes
In what follows, we denote by \(\vee\) the maximum and by \(\wedge\) the minimum, and a bar over a distribution function denotes its tail: \({\bar{F}}(x)=1-F(x)\).
As compared to Definition A, the change of variables \(s=e^{-\tau}\) is made and accordingly the functions \(u_{n}\) (\(n\geqslant 1\)) are redefined.
REFERENCES
M. R. Leadbetter, G. Lindgren, and H. Rootzén, Extremes and Related Properties of Random Sequences and Processes Springer Series in Statistics (Springer, New York, 1983). https://doi.org/10.1007/978-1-4612-5449-2
P. Embrechts, C. Klüppelberg, and T. Mikosh, Modelling Extremal Events for Insurance and Finance (Springer, Berln, 2003).
L. de Haan and A. Ferreira, Extreme Value Theory: An Introduction, Springer Series in Operations Research and Financial Engineering (Springer, New York, 2006). https://doi.org/10.1007/0-387-34471-3
S. Yu. Novak, Extreme Value Methods with Applications to Finance, Monographs on Statistics and Applied Probability, vol. 122 (CRC Press, Boca Raton, Fla., 2012).
A. V. Lebedev, ‘‘Extremal indices in a series scheme and their applications,’’ Inf. Primen. 9 (3), 39–54 (2015). https://doi.org/10.14357/19922264150305. English translation in arXiv:2009.09469 [math.PR]
A. V. Lebedev, ‘‘Nonclassical problems of stochastic theory of extremes,’’ Doctoral Dissertation in Physics and Mathematics (Lomonosov Moscow State Univ., Moscow, 2016).
A. A. Goldaeva and A. V. Lebedev, ‘‘On extremal indices greater than one for a scheme of series,’’ Lith. Math. J. 58, 384–398 (2018). https://doi.org/10.1007/s10986-018-9407-2
N. M. Markovich and I. V. Rodionov, ‘‘Maxima and sums of non-stationary random length sequences,’’ Extremes 23, 451–464 (2020). https://doi.org/10.1007/s10687-020-00372-5
N. M. Markovich, ‘‘Extremes of sums and maxima with application to random networks,’’ (2020). arXiv:2110.04120 [math.PR]
R. B. Nelsen, An Introduction to Copulas, Springer Series in Statistics (Springer, New York, 2006). https://doi.org/10.1007/0-387-28678-0
A. J. McNeil, R. Frey, and P. Embrechts, Quantitative Risk Management (Princeton Univ. Press, Princeton, 2005).
Yu. N. Blagoveshchenskii, ‘‘Main elements of copula theory,’’ Prikl. Ekonometrika 26 (2), 113–130 (2012).
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Translated by I. Tselishcheva
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Lebedev, A.V. The Possibility of Existence of Extremal Indices Exceeding One. Moscow Univ. Math. Bull. 77, 1–6 (2022). https://doi.org/10.3103/S0027132222010041
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DOI: https://doi.org/10.3103/S0027132222010041