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The kurtosis (or excess)  measures the relative flatness of a distribution (as compared to the normal distribution, which shows a kurtosis of zero). A positive kurtosis indicates a tapering distribution (also called leptokurtic distribution), whereas a negative kurtosis indicates a flat distribution (platykurtic distribution). The kurtosis is defined by the following formula:

Below you find two examples of distributions with different kurtosis.


Note that the kurtosis is sometimes defined by another formula, omitting the term "-3" in the formula above. In this case a normal distribution would yield a kurtosis of 3.

Last Update: 2005-Jul-16