Accuracy and Precision Defined
ACCURACY, NOT PRECISION
Are you using the words precision and accuracy correctly, or do you believe they essentially mean the same thing? If you use them interchangeably, you’re not alone. Dictionaries use one word to define the other, even dictionary.com:
precision “accuracy; exactness”
accurate “precise; exact”
To find the BEST definitions I had to keep scouring the internet.
PRECISION | The Correct Definition
Thoughtco.com: Precision is how consistent results are when measurements are repeated. Precise values differ from each other because of random error, which is a form of observational error.
ACCURACY | The Correct Definition
Thoughtco.com: In math, science, and engineering, accuracy refers to how close a measurement is to the true value. The ISO (International Organization for Standardization) applies a more rigid definition, where accuracy refers to a measurement with both true and consistent results. The ISO definition means an accurate measurement has no systematic error and no random error. Essentially, the ISO advises the term accurate be used when a measurement is both accurate and precise.”
ACCURACY vs PRECISION
Do you see the subtle but significant difference? The most popular example is a bullseye.
The picture on the left is accurate: the cluster isn’t very tight, but it is around the red center. The middle picture is precise: it has a tight cluster, but it is away from the center. The last picture is accurate AND precise: there’s a tight cluster over the red center.
USING IT THE RIGHT WAY
I really believe that words matter, and when at all possible, I try and use the BEST word. It’s easy to forget which word to use. So how can I remember it correctly? Attention to Accuracy, NOT Attention to Precision! I use alliteration to help me remember. Attention to Accuracy. It works for me, and it’ll work for you too!