The kurtosis is a statistical key figure. It analyses the extent to which a frequency distribution deviates from the normal distribution. The excess kurtosis is the difference between the kurtosis of a curve and that of a normal distribution. The kurtosis of a normal distribution is 3. If a frequency distribution has an excess greater than zero, the distribution is steeply peaked. If, on the other hand, the excess is less than zero, the distribution is flat-peaked and shows so-called fat tails.