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KeynesYang · 2020年02月17日

问一道题:NO.PZ201709270100000305

* 问题详情,请 查看题干

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.

textadjustedR2=1(n1nk1)(1R2text{adjusted R}^\text{2}=1-(\frac{n-1}{n-k-1})(1-R^2

看了前面的解答,想问下,这个题不用计算具体的adjusted R2就可以直接得结论吗?

1 个答案
已采纳答案

星星_品职助教 · 2020年02月18日

同学你好,

理论上计算一下更为严谨。但这道题想考察的不是计算(也没法计算,因为增加一个变量后,从RSS到TSS都是变化的),而是想考察概念,所以才给了相关系数,和要求根据表格解题。

考察是概念,如果一个新增变量对模型贡献度不大的话,那么adj.R2是下降的。

 

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