Tweeted twitter.com/#!/StackStats/status/315550484888961024
2 edited title
| link

Standard Deviationdeviation of Revenuerevenue where numbers are only positive

1
source | link

Standard Deviation of Revenue where numbers are only positive

Is there a way for standard deviation to ignore negative numbers? In other words, how can you make it so that 2 or 3 deviations do not extend into negative territory?

When looking at a set of only positive numbers, within one or two standard deviations, I end up with negative numbers. It's essentially impossible for a data point to be negative. Am I doing something wrong?

Also, when using deviations from the mean, do you add or subtract the full deviation from the mean or divide by two and plus and minus that to get one deviation from mean

I'm sure this embarrassingly simple for this group but this is not my strong point!

Please let me know if I can clarify. My recent experience with statistics is relatively limited.

Thanks!