Difference Between Precision and Accuracy

There’s quite a bit of confusion between these two terms. Basically, precision is simply the ability to deliver repeatable results. In this example of a shot group from a rifle, you can see that the cluster of holes is fairly tight. It has a small spread, so is precise.

Precise, but not accurate

The process that the shooter used was consistent, and the gun was capable of shooting in the same spot time after time. So, what’s the difference between precision and accuracy?

An accurate process, by definition, is one that centers on the desired outcome. In this second picture, if you average out the location, the shooter is hitting the bulls-eye. He is shooting with accuracy. It just isn’t what normally comes to mind when one thinks of an ‘accurate’ process, since he is all over the target.

Accurate, but not precise

What people generally think of when they envision a ‘good’ process is one that is both accurate and precise-one that both centers on the target and has a small spread.

Centered. Accurate and precise.

So, in practice, the difference between precision and accuracy is irrelevant. You need both for a process to be effective. A widely spread shot group that is ‘accurate’ is just as useless as a ‘precise’ process that is well off the mark.

Learn more about this topic in the accuracy entry of The Continuous Improvement Companion.