\(Y=\alpha_{0}+\beta_{0}P_{\text{ev}}\ +\ \alpha_{1}x_{1}+\beta_{1}x_{1}P_{\text{ev}}+\ \alpha_{2}x_{2}+\beta_{2}x_{2}P_{\text{ev}}+\alpha_{3}x_{3}+\beta_{3}x_{3}P_{\text{ev}}+\alpha_{4}x_{4}+\beta_{4}x_{4}P_{\text{ev}}+\varepsilon\) (1)