What's a fair way to adjust value for consistency?
For example, Machine A pumps out 10 lollipops every day. Machine B pumps out 0 lollipops one day and 20 lollipops the next, which averages 10 lollipops a day (you just don't know when you'll get 0 or 20). I want to adjust the 10 lollipops per day numbers in this example for consistency, giving a better value for the more consistent machine. How should I do this? I have logs of all machine output.
Don't know how to tag this.
You want the standard deviation.
First, define the variance, which is the average of the square of the offset. In your example, the first machine is always at 10, so the offset is zero, and the variance is zero. In the second machine, the offset is either 20-10=10 or 0-10=-10. The square in both cases is $10^2=100$ or $(-10)^2=100$, so the variance is 100.
The standard deviation is the square-root of the variance. In this case it is 0 for the first machine and 10 for the second machine.
Usually, you keep both numbers - the mean and the standard deviation - rather than combine them. So you know the (10,0) machine is more reliable than the (10,10) machine, but both give the same output in the long run.
