if fact this result holds for any case in with the mean of t of the observation is x and the mean of the remaining observation is x+x since the order of the observation is not relevant in computing x therefore x is biased upward and consequently x=x/x will tend to overestimate x note that the extent of the bias in x depends on the magnitude of the shift in the mean x the time period following which the shift occurs (t) and the number of available observation (m) now the moving range is only impacted by the shift in the mean during open period (t+1) so the bias in x depends only on the shift magnitude and m if 1