The variability of the mean (μ) is called the standard error (s.e.) of the mean (or just s.e.), and is often drawn as little ‘error bars’ on graphs or histograms, to give you some idea of the accuracy of the average measure. If the mean is averaged over a sample of N independent items, the standard error is σ/√N – where σ is the standard deviation of the sample or the standard deviation (s.d., σ) of a single item if that is already known.

Defined on page 107

Used on page 107

Also known as s.e.