Coefficient of variation: compare spread across different averages
Learn when standard deviation divided by the mean is meaningful, with a comparison of two sample groups.
How it works
The coefficient of variation, CV, is standard deviation divided by the absolute mean, usually expressed as a percentage. It scales the spread to the typical value, which can help compare groups with different means. Use the same sample or population definition for both standard deviations. A CV of 10% does not mean ten percent of observations are outliers.
Use the inputs from your own situation and keep the units consistent. A calculator gives an arithmetic estimate under the assumptions you enter; compare it with real records before making a decision.
Worked example
Group A has mean 50 and standard deviation 5: CV = 5 ÷ 50 = 10%. Group B has mean 200 and standard deviation 30: CV = 30 ÷ 200 = 15%. B has a larger relative spread despite its higher average. For a small sample, show the data distribution as well as the summary.
What to check
The CV becomes unstable when the mean approaches zero and is not useful for quantities with arbitrary zero points, such as Celsius temperature. Strong skew or outliers can also mislead. Check units, sample size, missing observations and whether the measurements are comparable before treating the lower CV as better.
Practical next step
Calculate each mean and standard deviation from the same type of observations, then compare CVs with a plot or ranges. Explain what the variability means in the actual process.
Related calculators and articles
coefficient variation, standard deviation. percentage change vs percentage points.
Save your assumptions and repeat the calculation if an input changes. The linked article explains a neighboring decision that this single formula does not settle.