If variables x and y come under the bivariate normal distribution, the relation between x and y is as follows :
y = α + β + ε
in which α and β are coefficients of regression, and ε a stochastic variable. The data obtained by applying this equation to the rainfall of Matsue and Hirata are believed to be more suitable for the population than the data estimated by the conventional equation of regression line y = α + βx.