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羊 · 2022年06月12日

请问为什么不用考虑截距项。谢谢

NO.PZ2015120204000021

问题如下:

Excess stock market returnt=a0+a1Default spreadt-1+a2Term spreadt-1+a3Pres party dummyt-1+et

Default spread is equal to the yield on Baa bonds minus the yield on Aaa bonds. Term spread is equal to the yield on a 10-year constant-maturity US Treasury index minus the yield on a 1-year constant-maturity US Treasury index. Pres party dummy is equal to 1 if the US President is a member of the Democratic Party and 0 if a member of the Republican Party.

Exhibit 1.Multiple Regression Output

The Pres party dummy variable in the model indicates that the mean monthly value for the excess stock market return is:

选项:

A.

1.43 percent larger during Democratic presidencies than Republican presidencies.

B.

3.17 percent larger during Democratic presidencies than Republican presidencies.

C.

3.17 percent larger during Republican presidencies than Democratic presidencies.

解释:

B is correct.

The coefficient for the Pres party dummy variable (3.17) represents the increment in the mean value of the dependent variable related to the Democratic Party holding the presidency. In this case, the excess stock market return is 3.17 percent greater in Democratic presidencies than in Republican presidencies.

或者包括j截距项的其他选项,

1 个答案

星星_品职助教 · 2022年06月13日

同学你好,

本题实际问的是dummy variable(Pres party dummy)的系数的含义。dummy variable的系数的含义是一个“difference”,即选项中的“larger”。

当Pres party dummy=1时,Excess stock market return=a0+a1Default spread+a2Term spread+3.17×1+et ①;

当Pres party dummy=0时,Excess stock market return=a0+a1Default spread+a2Term spread+3.17×0+et ②;

将上述方程①和②相减,可以看出此时两个方程正好差了3.17,即Pres party dummy的系数,截距项和其他项都在这个过程中被消去了。