In Reply to Parent Post by Statistical Steven
I wish Microsoft would do away with the STDEVP function. It has no use. The difference is that STDEV divides by n-1 and STDEVP divides by n. Can anyone tell me when you would use STDEVP?
I think I've also answered this on the ASQ board from a question there. But here goes:
The formula for sigma (STDEVP) is the maximum likelihood estimator for the population standard deviation. However, it is a biased estimator. If you only have a sample of the population (and consider - if the "future" is part of your population, you still only have a sample), STDEVP will have a bias in it. If you repeatedly sample from a population, you will notice that the average STDEVP values will not tend to match the actual population standard deviation. However, if you use STDEV (dividing by n-1), the average of the STDEV's will converge on the population standard deviation.