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Basic Math/Percent Difference

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Question
Hi Abe,

I am comparing two sets of numbers. A forecast number and an actual number. I'd like to measure the percent difference of the actual number in relation to the forecast number. The numbers will be positive, negative, and in some cases zero.

Sample Data:

Forecast Number          Actual Number
161          157
74          0
24          -12

Thanks for the help!

Answer
Hello Jesse,

If you are comparing the percent difference in the actual from the predicted, then it is:
100% X (actual-predicted)/predicted.

Thus, for 157 vs 161 it is 100% * (157-161)/161 about -2.48%
For 0 vs 74 it is 100% * (0-74)/74 = -100%
For -12 vs 24 is is 100% * (-12-24)/24 = -150%

OK?

Abe

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Abe Mantell

Expertise

Hello, I am a college professor of mathematics and regularly teach all levels from elementary mathematics through differential equations, and would be happy to assist anyone with such questions!

Experience

Over 15 years teaching at the college level.

Organizations belong to
NCTM, NYSMATYC, AMATYC, MAA, NYSUT, AFT.

Education/Credentials
B.S. in Mathematics from Rensselaer Polytechnic Institute
M.S. (and A.B.D.) in Applied Mathematics from SUNY @ Stony Brook

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