Moreover, the experimental and predicted Cu leaching efficiencies are presented in Table and ). This is because the Cu content in the PCB sheets varies widely . of the independent variable(s) . A p-value less than 0.05 at a 95% confidence interval generally indicates the high significance of the independent variable in influencing the dependent variable or outcome . The p-value of the model terms X3, X2 2 , X3 2 , and X1X2