In Problems 19–22, find the value of ȥ∝
ȥ0.025
Step 1 of 5) In general, if there are c categories for a qualitative explanatory variable, the regression model will require c − 1 indicator variables, each taking on a value of 0 or 1. Objective. Find a Quadratic Regression Equation. Find a Quadratic Regression Equation We mentioned that a regression model can include quadratic terms. For example, a complete second-order model with two explanatory variables x1 and x2 is yi = b0 + b1x1i + b2x2i + b3x1ix2i + b4x1i 2 + b5x2i 2 + ei Scatter diagrams of the response variable drawn against each explanatory variable are used to determine the type of relation that may exist between the two variables. In this section, we consider quadratic models of the form yi = b0 + b1x1i + b2x1i 2 + ei. Once a quadratic model is obtained, we go through the usual analysis of (1) drawing residual plots to verify the model is appropriate, (2) performing an F-test for lack of fit, and (3) testing individual regression coefficients for significance.