How to Calculate a Geometric Mean with negative numbers

[Ankit_Kumar]

Hello Everyone,

I want to create the geometric mean of a series of values in which some values are negative for example: - investment over a series of years with some negatives.
My problem is Geomean function is not working as it only works for positive numbers.
Please suggest which formula I can apply.


Thanks
Ankit

[MrShorty]

According to Wikipedia (http://en.wikipedia.org/wiki/Geometric_mean ), the standard definition of geometric mean (the nth root of the product of n numbers) only applies to non-negative numbers. The first step to taking the geometric mean of a data set that includes negative numbers will be to define what is meant (mathematically) by geometric mean when negative numbers are involved. Once you define the mathematical function, then we can help you figure out how to program that function into Excel.

[MrShorty]

As an additional thought, this site makes some suggestions for "negative" numbers: http://buzzardsbay.org/geomean.htm about 2/3 of the way down. See if either of those strategies will apply to your data.

[shg]

Your question is impossibly vague, but an investment can never have a negative return unless you're dealing with Vinnie the Shark.

If you invest $100 and get $95 back, your return isn't -5%, it's 95%, and that can be readily used in a geometric mean.