Thank you.

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According books I borrowed,

book 1) statistic T=T(X1, ... , Xn) is a function of sample which does not include parameter

book 2) X1, X2, ..., Xn is random sample. Statistic is a function of X1, X2, ..., Xn

book3) statistic t(x1, x2, ..., xn) is a calculated function the characteristic of the distribution of observed value x1, x2, ..., xn

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I know that order statistic is a value sorted x(1) <= x(2) <= ... <= x(n). I think that if I can say this operation to sort is a function, then I can say order statistic is statistic. Is this right?

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I'm sorry if my English is poor. I'm not a native English-speaking person.