Model Selection: Adjusted Coefficient of Determination-Variance Tradeoff

In my previous article, we analyzed the COVID-19 data of Turkey and selected the cubic model for predicting the spread of disease. In this article, we will show in detail why we selected the cubic model for prediction and see whether our decision was right or not. When we analyze the regression trend models we should consider overfitting and underfitting situations; underfitting indicates high bias and low variance while overfitting indicates low bias and high variance. The adjusted coefficient of determination is used in the different degrees of polynomial trend regression models comparing. When we examine the above formulas, we can notice the similarity between SSE and bias.