Kurtosis is the degree of peakedness of a distribution, defined as a normalized form of the fourthof a distribution. There are several flavors of kurtosis commonly encountered, including the kurtosis proper, denoted or defined by
where denotes the th(and in particular, is the ). This form is implemented in as [dist].
The kurtosis "excess" is denoted or , is defined by
and is implemented inas [dist]. Kurtosis excess is commonly used because of a is equal to 0, while the kurtosis proper is equal to 3.
Unfortunately, Abramowitz and Stegun (1972) confusingly refer to as the "excess or kurtosis."