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Published online by Cambridge University Press: 24 August 2016
We extend some results of the extreme-value theory of stationary random sequences to non-stationary random sequences. The extremal index, defined in the stationary case, plays a similar role in the extended case. The details show that this index describes not only the behaviour of exceedances above a high level but also above a non-constant high boundary.
Part of this research was done while the author was at the Center for Stochastic Processes at Chapel Hill. The author wishes to express his gratitude for the financial support and the hospitality.