Kurtosis

Kurtosis is a Greek word (κυ´ ρτωσις) denoting curvature, from kurtos (κυρτο´ ς) meaning convex or curved. (It is used in geometry to refer to the appearance of convex figures and in medicine to refer to the curvature of the spine seen in kyphosis. Greek writers prefer to render the word in English as kyrtosis.) Kurtosis was adopted by the British mathematician and statistician Karl Pearson in 1905 to describe the shape of frequency distributions in comparison with that of a normal curve: “If more flat-topped I term them platykurtic [i.e., of broad curvature], if less flat-topped leptokurtic [of thin curvature], and if equally flat-topped mesokurtic [of intermediate curvature]” (p. 173). Pearson went on to provide a quantitative definition of kurtosis that has since been ...