# What is percent difference really doing.

#### noetsi

##### Loves R
This is (a1-b1)/ ((a1+B1)/2) and is a way a former poster suggested I use to compare two numbers. I have done so a lot for years, but this week I began to wonder how wise that is. The problem is that really huge differences seem to be understated.

For example numbers that are 3 times as large as another number show percent differences of say 99%. Which seems to me very low.

So what is percent difference really telling you substantively. Remember this goes to audiences that know nothing of statistics or much of math.

#### Miner

##### TS Contributor
First define the question that you want to answer then determine whether that question is better answered by the difference in values or by the percentage change. One is not inherently better than the other. They just provide different information and answer different questions.

Both can be misused to lie with statistics.

#### noetsi

##### Loves R
We are having a debate at work which is best. One prefers variance, to me percent different is better because it gets around units and scale. Compare two numbers 1 and 10 and 10 and 100. With variance the way they use it (simply the difference between two numbers) these lead to very different results. When you use percent difference they lead to the same result.