Get the coefficient of variation, also called relative standard deviation (RSD), to compare spread between data on different scales.
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CV = s ÷ |x̄| × 100 = 1.4599 ÷ 99.9 × 100
| Mean (A) | 99.9 |
|---|---|
| SD (A) | 1.4599 |
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An SD of 5 kg is enormous for newborn weights and trivial for adult elephants. Dividing by the mean removes the scale: newborns averaging 3.4 kg with SD 0.5 kg have a CV of about 15%, while elephants averaging 4,000 kg with SD 500 kg have 12.5%. Relative to their size, elephants vary slightly less.
The CV is built from the standard deviation and the mean; if your data are strongly skewed, compare IQR ÷ median instead.
The standard deviation divided by the mean, usually as a percentage. It expresses spread relative to the size of the values, so you can compare variability between data sets with different units or very different means.
Yes. Chemists and lab scientists usually say RSD or %RSD; other fields say coefficient of variation. The calculation is the same.
It depends on the field. Many analytical labs aim for an RSD below 2% on replicate measurements, while biological assays often accept 10–15%. In finance, CV compares risk per unit of return. There is no universal threshold.
When the mean is near zero (CV explodes), when the data can be negative, or when the measurement scale has no true zero, like temperature in Celsius. It is meaningful for ratio-scale data such as mass, length or counts.