What is precision?

1 Answer

Precision is a way of measuring the closeness of a set of answers to the others presented by the experimenter; that is, it is a measure of consistency or reproducibility.


Throughout chemistry there's a big difference between two large terms. Accuracy vs Precision. There's also a big difference between them.

Let's start with accuracy. Let's say the accepted answer to a problem is 1. Here's the accurate dataset of answers that your class got.
#[1, 2, 1, 0, 1, 1, 1.5, 0.5, 1]#
As you can see, most answers are very close to 1.
An accurate answer is very close to the accepted result. If the accepted answer is 4 and you got 3.9 while everyone else got 0, your answer is the most accurate.

Now, what about precise? Let's take a look at a data set. The accepted answer will be 1 again.
#[50, 51, 49, 50.1, 48.9, 50, 50, 50]#
As you can see, none of these answers are remotely close to 1. However, they are all very precise to each other.
A precise answer is very close to the other answers, but not necessarily close to the accepted answer. If the accepted result is 5 and you got 200, your answer is precise if the rest of the class gets answers close to 200.

Here's an infographic that helps explain.
Google Images, thanks google.