TABLE 13-11 A Weight-Loss Clinic Wants to Use Regression Analysis to Build

TABLE 13-11
A weight-loss clinic wants to use regression analysis to build a model for weight loss of a client (measured in pounds) . Two variables thought to affect weight loss are client's length of time on the weight loss program and time of session. These variables are described below:
Y = Weight loss (in pounds)
X1 = Length of time in weight-loss program (in months)
X2 = 1 if morning session, 0 if not
X3 = 1 if afternoon session, 0 if not (Base level = evening session)
Data for 12 clients on a weight-loss program at the clinic were collected and used to fit the interaction model:
Y = β0 + β1X1 + β2X2 + β3X3 + β4X1X2 + β5X1X3 + ε
Partial output from Microsoft Excel follows:

-Referring to Table 13-11, in terms of the βs in the model, give the mean change in weight loss (Y) for every one-month increase in time in the program (X₁) when attending the afternoon session.

A) β₁ + β₄
B) β₁ + β₅
C) β₁
D) β₄ + β₅