In the equation \( R^2 = \frac{\text{SSM}}{\text{SST}} \), the blank should be filled with "SSM," which stands for the sum of squares due to the model (or regression sum of squares).
So, the complete equation is:
\( R^2 = \frac{\text{SSM}}{\text{SST}} \)
Where:
- \( R^2 \) is the coefficient of determination,
- \( \text{SSM} \) is the regression sum of squares,
- \( \text{SST} \) is the total sum of squares.