Difference between uncertainty and accuracy? (1 Viewer)

matthewmorrison123

New Member
What is the difference between uncertainty and accuracy? I've been reading through some NESA documents and they seem to use the two words interchangeably. Is there a difference? Thanks

wizzkids

Active Member
Yes, I share your pain. These words are more often than not used incorrectly. We have to be so careful to define words like precision, accuracy and uncertainty, but I'm happy to give it a go. Precision means how many significant figures you can give for a result. Accuracy means how close is the result to the true value (or the consensus value in the scientific literature). Uncertainty is the spread of results that you estimate together with the result. This means you can have a very precise result, that is completely wrong (inaccurate). Typically this can happen when there is an uncontrolled variable, that you did not take into account. Here is an actual example: the rest mass of the electron. This has been measured to high precision many times in many different ways. The accepted value is 9.109 383 7015 x 10-31 kg with a standard uncertainty of +/- 0.000 000 0028 x 10-31 kg. A scientist looking at these data would recognise that those last two significant figures "15" in the value cannot be relied upon. It could be as high as (15 + 28) or as low as (15 - 28). By the way, these data come from the United States National Institute of Standards and Technology (NIST).
Does that help?

Last edited:

matthewmorrison123

New Member
Yes, I share your pain. These words are more often than not used incorrectly. We have to be so careful to define words like precision, accuracy and uncertainty, but I'm happy to give it a go. Precision means how many significant figures you can give for a result. Accuracy means how close is the result to the true value (or the consensus value in the scientific literature). Uncertainty is the spread of results that you estimate together with the result. This means you can have a very precise result, that is completely wrong (inaccurate). Typically this can happen when there is an uncontrolled variable, that you did not take into account. Here is an actual example: the rest mass of the electron. This has been measured to high precision many times in many different ways. The accepted value is 9.109 383 7015 x 10^-31 kg with a standard uncertainty of +/- 0.000 000 0028 x 10^-31 kg. A scientist looking at these data would recognise that those last two significant figures "15" in the value cannot be relied upon. It could be as high as (15 + 28) or as low as (15 - 45). By the way, these data come from the United States National Institute of Standards and Technology (NIST).
Does that help?
Yes. Thank you so much! That clears up my confusion :0