Functional data analysis (FDA) is a part of modern multivariate statistics that analyses data providing information about curves, surfaces or anything else varying over a certain continuum. In economics and other practical applications we often have to deal with time series of functional data, where we cannot easily decide, whether they are to be considered as stationary or nonstationary. However the definition of nonstationary functional time series is a bit vogue. Quite a fundamental issue is that before we try to statistically model such data, we need to check whether these curves (suitably transformed, if needed) form a stationary functional time series. At present there are no adequate tests of stationarity for such functional data. We propose a novel statistic for detetecting nonstationarity in functional time series based on local Wilcoxon test.
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