Maybe this is a dumb question, but is it valid to have a negative percent below -100% when comparing two quantities?
I'm evaluating the Net Present Value of an investing project affected by many external variables. The expected NPV of the project is 122961$. When affected by external varialbes, the worst case scenario makes the NPV equal to -11128, which means a deviation of -109%. Does this have a valid meaning?
Yes, it makes sense.
You are saying that the worst-case NPV is $109\%$ less than the expected NPV.
However, it just sounds a little awkward, but the point comes through.
It sounds normal to say "stocks increased $200\%$" to represent stocks tripling in value, but since $-100\%$ means $0$, it's not common to use such percentages.