What is precision?

Aug 27, 2016

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.

Explanation:

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.
$\left[1 , 2 , 1 , 0 , 1 , 1 , 1.5 , 0.5 , 1\right]$
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.
$\left[50 , 51 , 49 , 50.1 , 48.9 , 50 , 50 , 50\right]$
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. 