Skewed distribution

Last revised by Candace Makeda Moore on 14 Sep 2020

A skewed distribution is a distribution similar to a normal distribution but it is asymmetrical i.e. it has a longer tail on one side than the other and may describe a probability distribution or data itself. While in a normal distribution the mean and median are the same, in a scewed distribution they are different. A positively scewed distribution will have a larger mean than median. Positively scewed distributions are sometimes called right scewed distributions because they have a long right tail (on the increasingly positive numbers). Negatively scewed distributions, or left scewed distributions, have a smaller mean than median.

Practical points

Although it is not uncommon for radiologists to refer to a skewed distribution as simply a non-normal or nonsymmetric distribution, and even some literature describes these distributions as such 1, it is so imprecise and confusing, these names are best avoided in most cases. There are many different kinds of distributions, many are not symmetric and only one is normal.

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