I understand that the difference between the two is whether or not the full population is being used (P) or just a sample of the population (S).
However, if I'm looking at historical sales data, and I want to calculate the Standard Deviation of only the past 6 months, should I be using P or S?
None of the data for the last 6 months is missing, and I'll be using the full 6 months, which leads me to believe I should be using P. However, if I have say 20 years of sales data at my finger tips, but I'm only looking at the past 6 months, does that mean I should actually be using S?
I only actually care about the deviation in the previous 6 months. So I do believe P is correct, but wanted to confirm with the gurus.
Calculate standard deviation within a certain range in excel - Stack Overflow
Why is my calculated standard deviation different from excel's? : excel
Either my understanding of Standard Deviation is off or Excel is wrong here. : AskStatistics
Geometric Standard Deviation in Excel?
If you don't mind using additional rows for the intermediate calcuations, you can do it this way: for D33:I33, calculate =LN(D33) through LN(I33). We'll say these are placed in D34:I34. From there, the geometric standard deviation is just =EXP(STDDEV(D34:I34)). You may be able to do this without the intermediate values by using arrays.