Accurate or Precise? What’s the Difference?

In IA assessment we usually get bogged down with errors and uncertainties. There are, however, more subtle concepts at large! Most students muddle up the words and ideas behind the terms ‘accurate’ and ‘precise’.


In order to understand these concepts it is important that you imagine that the ‘thing’ you are measuring has a ‘true value’ and accuracy and precision are measured with respect to this ‘true’ value.

An accurate measurement will give a result nearer to the true value. It is likely to be more sensitive to changes (eg, it may have more decimal places).

Precision is connected to the smallest scale measuring instrument that you are using. It will also give consistent readings when used repeatedly.

These ideas are commonly visualised when thinking of a person throwing darts at a dart board:

Accurate and precise:

Inaccurate but precise:

Inaccurate and imprecise:

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