A.1.10—Dispersion, standard deviation and range

Range gives the distance from the smallest to largest value; standard deviation summarises typical spread around the mean. Both describe variability, not the cause of it.

Use the same units as the measurements, inspect outliers and report a spread alongside the centre. Do not compare spreads without considering scale and sample size.

Two groups can have the same mean growth rate but different standard deviations; the second group is less consistent even though its average matches.

A small standard deviation does not prove the measurements are accurate; they may be consistently biased.