Db. Percival, 3 CURIOUS PROPERTIES OF THE SAMPLE VARIANCE AND AUTOCOVARIANCE FOR STATIONARY-PROCESSES WITH UNKNOWN MEAN, The American statistician, 47(4), 1993, pp. 274-276
In most books on time series analysis, estimators of the variance and
autocovariance for a stationary process are discussed under the assump
tion that the process mean is known. Here we illustrate that, if the p
rocess mean is unknown and hence is estimated by the sample mean, thes
e estimators have some surprising properties.