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Consider the following 2 regression models:
Model 1:
Model 2:
A researcher determines that the two models have identical R-squared values. This most likely implies that:
A
Model 2 must have a lower value of adjusted R-squared
B
Model 2 must have a higher value of adjusted R-squared
C
Model 1 and 2 will also have identical values of adjusted R-squared
D
Variable is statistically significant
Explanation:
When two regression models have identical R-squared values, it means the additional variable has zero explanatory power for and its coefficient estimate must be exactly zero. The adjusted R-squared formula is:
where represents the number of regressors. Since Model 2 has more regressors (k increases from 2 to 3) while R-squared remains the same, the denominator decreases, making the fraction larger. This causes the adjusted R-squared for Model 2 to be lower than for Model 1. Therefore, Model 2 must have a lower value of adjusted R-squared.