I am trying to work out the percentage difference between two numbers (one of which is negative), NOT PERCENTAGE CHANGE. I have done quite a bit of reading, but there doesn't appear to be a definitive answer. Where both numbers are positive, I have been using the formula listed on the following site (https://www.calculatorsoup.com/calculators/algebra/percent-difference-calculator.php). If both numbers are negative, I simply input the absolute values, making them positive. I have issues arise when one of the numbers is negative – for instance:
The percentage difference between 1.6 and -8.8. If I use the formula in the link above, it provides me a result of -293%, but I'm not sure if this is correct – from a methodological stand point. Is this something that would be frowned upon in the mathematics world?
Cheers, Bosshard
Best Answer
The percentage difference is defined as the difference of the values, divided by the average and written in percentage. If you have two values, the formula is $\frac{|x-y|}{\frac{x+y}{2}} \times 100$. This also holds for negative numbers.
Remark:
(1) It is better known as relative change in percentage, for example here https://en.m.wikipedia.org/wiki/Relative_change_and_difference.