Table I.

Common error bars

Error barTypeDescriptionFormula
RangeDescriptiveAmount of spread between the extremes of the dataHighest data point minus the lowest
Standard deviation (SD)DescriptiveTypical or (roughly speaking) average difference between the data points and their meanEmbedded Image
Standard error (SE)InferentialA measure of how variable the mean will be, if you repeat the whole study many timesSE = SD/√n
Confidence interval (CI), usually 95% CIInferentialA range of values you can be 95% confident contains the true meanM ± t(n–1) × SE, where t(n–1) is a critical value of t. If n is 10 or more, the 95% CI is approximately M ± 2 × SE.