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benniewang · 2019年11月06日

问一道题:NO.PZ201709270100000305

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问题如下:

5. Based on Exhibit 2, Quinni’s best answer to Varden’s question about the effect of adding a third independent variable is:

选项:

A.

no for R2 and no for adjusted R2.

B.

yes for R2 and no for adjusted R2.

C.

yes for R2 and yes for adjusted R2.

解释:

B is correct. When you add an additional independent variable to the regression model, the amount of unexplained variance will decrease, provided the new variable explains any of the previously unexplained variation. This result occurs as long as the new variable is even slightly correlated with the dependent variable. Exhibit 2 indicates the dividend growth rate is correlated with the dependent variable, ROE. Therefore, R2 will increase.

Adjusted R2, however, may not increase and may even decrease if the relationship is weak. This result occurs because in the formula for adjusted R2, the new variable increases k (the number of independent variables) in the denominator, and the increase in R2 may be insufficient to increase the value of the formula.

[#PZMATH1337#]

我有点困惑,这个adjusted R^2是单调递减的么?还是随着k的上升先上升再下降?

1 个答案

星星_品职助教 · 2019年11月06日

同学你好,

这道题不用考虑那么复杂,对于adj R2你上次提问的理解是没问题的,adj R2是增加还是减小要取决于新增加进来的变量对模型的贡献程度。这道题adj R2直接选下降的考点是因为根据底下的相关系数矩阵,可以看出新增加的变量Div跟Y的相关性很小,只有0.117,所以新增这个变量对Y的解释力度很小,这个时候就会导致Adj R2下降。

CFA对于数学的要求没那么高,不会去考察具体adj R2的变化路径的,加油

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