请问为什么不用考虑截距项。谢谢

问题如下：

Excess stock market return_t=a₀+a₁Default spread_t-1+a₂Term spread_t-1+a₃Pres party dummy_t-1+e_t

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.