问题如下:
6. Based on the regression output in Exhibit 3 and sales data in Exhibit 4, the forecasted value of quarterly sales for March 2016 for PoweredUP is closest to:
选项:
A.$4.193 billion.
B.$4.205 billion.
C.$4.231 billion.
解释:
C is correct. The quarterly sales for March 2016 is calculated as follows:
beginarraylln Salest-ln Salest-1=b0+b1(ln Salest-1-ln Salest-2)+b2(ln Salest−4-ln Salest-5)ln Salest−ln3.868=0.0092−0.1279(ln3.868−ln3.780)+0.7239(ln3.836−ln3.418)ln Salest=1.44251Salest=e1.44251=4.231
老师请问,一阶差分的方程是不是需要我们自行推导?因为题目不会给我们。为何一阶差分后是ln Salest-ln Salest-1=b0+b1(ln Salest-1-ln Salest-2)+b2(ln Salest−4-ln Salest-5)而不是ln Salest-ln Salest-1=b0+b1(ln Salest-1-ln Salest-2)+b2(ln Salest−3-ln Salest-4)?