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On Wikipedia, a statistic is defined to be an observable random variable ( ). However, neither of the terms statistic and observable is formally defined in the article. So what exactly is a statistic?

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What is wrong with a function of a sample where the function itself is independent of the sample's distribution; that is, the function can be stated before realization of the data. The term statistic is used both for the function and for the value of the function on a given sample? – Did Jan 4 '13 at 23:31
From the information provided in your question, "statistic" is formally defined: in terms of "observable". It is just the latter term that is not defined. – John Bentin Jan 5 '13 at 15:05
@did: There's nothing wrong with it, but I was looking for a rigorous definition in terms of probability spaces and functions on them. – Benno Jan 6 '13 at 12:58

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