Aaron has two interval-level independent variables and an interval-level dependent variable. His R² value is 0.110.

a. Aaron adds another independent variable, and this increases the R² to 0.155. What does this say about the contribution of the new variable?

b. Aaron adds a fourth independent variable to the statistical model, and this does not increase the R² value any further, and the null hypothesis for the new variable’s β value is not rejected. What does this say about the contribution of this additional new variable?