A note on the skewness of the frequency distribution of harvest indices with an application to winter oilseed rape (Brassica napus L.)

Based on well-known statistical approximations for the mean. variance, and for the third moment about zero of the ratio of two random variables, a general expression has been derived for the skewness of the distribution of harvest indices. The skewness of the distribution of harvest indices depends on three parameters: coefficients of variation for the two component traits and their correlation. Conclusions for the sign of this skewness are discussed. Finally, the theoretical results and conclusions have been checked and applied to an experimental data set of winter oilseed rape. The agreement between expected and observed skewness is extraordinary good.