Any real-valued function T= r (XXn) of the observations in the random sample is called a statistic. Three examples of statistics are the sample mean X'n the maximum Yn of the values of XXn; and the function r(X Xn), which has the constant value 3 for all values of XXn In an estimation problem. we can say that an estimator of 0 is a statistic whose value can be regarded as an estimate of the value of 0