What is the interpretation of the slope β1\beta_1β1 in the model Y=β0+β1X1+β2X2+β3(X1⋅X2)+ϵY = \beta_0 + \beta_1 X_1 + \beta_2 X_2 + \beta_3 (X_1 \cdot X_2) + \epsilonY=β0+β1X1+β2X2+β3(X1⋅X2)+ϵ?
The effect of X1X_1X1 on YYY when X2=0X_2 = 0X2=0.
The average effect of X1X_1X1 on YYY regardless of X2X_2X2.
The effect of X2X_2X2 on YYY when X1=0X_1 = 0X1=0.
The combined effect of X1X_1X1 and X2X_2X2 on YYY.