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周梅 · 2024年09月03日

Quantitative

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NO.PZ202208220100000302

问题如下:

Identify the type of error and its impacts on regression Model A indicated by the data in Exhibit 2.

选项:

A.Serial correlation, invalid coefficient estimates, and deflated standard errors. B.Heteroskedasticity, valid coefficient estimates, and deflated standard errors. C.Serial correlation, valid coefficient estimates, and inflated standard errors.

解释:

A is correct. The Breusch–Godfrey (BG) test is for serial correlation, and for Model A, the BG test statistic exceeds the critical value. In the presence of serial correlation, if the independent variable is a lagged value of the dependent variable,then regression coefficient estimates are invalid and coefficients’ standard errors are deflated, so t-statistics are inflated.

Serial correlation, 为什么是invalid coefficient estimates, 我看视屏讲解里归纳是不影响estimates和consisitency

1 个答案

袁园_品职助教 · 2024年09月04日

嗨,爱思考的PZer你好:


这里判断是根据这个条件来的。

我们在基础班讲义里面说过,当这个自变量是因变量的滞后项时(因变量是Yt,自变量中有Yt-1),这个系数估计是无效的。


注意:这里和下面的正向序列相关是两回事。正向序列相关是指残差项自己和自己相关,但自变量中没有因变量的滞后项,也就是红框里面的第一种情况,系数估计有效,但standard error无效;但是如果是自变量是因变量的滞后项这种情况,说明这个残差项是和因变量相关的,这个情况下系数估计也是无效的,standard error也无效。

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虽然现在很辛苦,但努力过的感觉真的很好,加油!

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