If only two groups are used (e.g., low-risk vs. high-risk), the regression model is similar to Equation 1. Let X1 represent the quantitative predictor, and D2 a dummy variable (0 = group 1, and 1 = group 2). The standard regression model is: (11)Yi=B0+B1X1i+B2D2i+B3(X1i·D2i)+Ei where D2i is the score of person i on dummy variable D2, the subscript 2 on D2i is a reminder that group 2 has the unit value on the dummy variable, and other symbols were defined above.
