普通最小二乘法的回归模型实际上只是一种基于条件均值的分析，即给定自变量X的情形下，刻画了因变量Y的均值。但在许多实际应用过程中，自变量X对因变量Y的影响随着Y的大小不同而不同。-The regression model of ordinary least squares is only a kind of analysis based on the conditional mean, that is, the mean of the dependent variable Y is given under the condition that the independent variable X is given. However, in many practical applications, the influence of the independent variable X on the dependent variable Y varies with the size of the Y.