I am trying to figure out a way of calculating the Z Scores on Minitab. I tried by entering all data (which includes the historical data and the data under observation) in one single column, clicked on 'Standardize' in Minitab and collected the results in the adjacent column. The problem I face is due to the value under observation. This value contributes to the Standard Deviation and Mean of the complete set of data and therefore it becomes difficult to correctly calculate the Z Score of that value. I wish to calculate the Z score of the value under observation using the mean and standard deviation of the available historical data.
Request advise from the members on performing this calculation.