What does skewness mean?
Skewness is most often a statistical term for the asymmetry of a probability distribution. It measures how far the distribution departs from perfect symmetry and is commonly expressed as a standardized third central moment. A positive value indicates that the right-hand tail is longer or heavier, while a negative value indicates the same on the left; zero is consistent with symmetry. In everyday discussion, “skewness” can also refer more generally to an uneven, tilted, or distorted condition. The word is chiefly formal and technical, so “skew” is often more convenient in general writing. It is distinct from bias, which concerns systematic error or unfair preference, and from kurtosis, which describes tail weight and peakedness. Knowing skewness helps readers interpret averages and visualize data: a mean can be pulled toward an unusually long tail even when most observations remain clustered together.
nounIn statistics, the degree to which a probability distribution is asymmetric, usually quantified by its standardized third central moment. More generally, the state of being unevenly slanted or distorted from a balanced or aligned form.
- The asymmetry of a probability distribution, especially as measured by its standardized third central moment.
- The state or quality of being skewed; unevenness or distortion from a balanced or aligned form.
"The unusually high skewness of the response distribution prompted the researchers to report the median alongside the mean."
"Positive skewness indicates that the distribution has a longer or heavier right-hand tail."
"The slight skewness of the photograph made the otherwise level horizon appear unstable."
The plural is used when comparing measures of asymmetry for multiple distributions or datasets.
"The researchers compared the skewnesses of the two income distributions."
Skewness reveals which way a distribution's long tail is pulling—and why its average may not tell the whole story.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does skewness come from?
Skewness was formed in English by adding the productive suffix -ness to skew. The adjective and verb skew descend from Middle English skewe, from an Old Norse word meaning slanting or oblique that is related to a Germanic root associated with shearing. Its specialized statistical meaning developed later as a name for a measure of distribution asymmetry.
Related word forms
How skewness is actually used
Chiefly a formal statistical term, although it can be used more generally for pronounced unevenness or distortion. Positive and negative values indicate direction only; they do not imply that a distribution is good or bad.
Easily confused with skewness
“Skew” can describe an uneven or biased condition, while “skewness” is especially the statistical quantity that measures a distribution's asymmetry.