Regression with interactions: Here is the output from a fitted linear regression of outcome y on pre-treatment predictor x, treatment indicator z, and their interaction:

Median MAD_SD

(Intercept) 1.2 0.2

x 1.6 0.4

z 2.7 0.3

x:z 0.7 0.5

Auxiliary parameter(s):

Median MAD_SD

sigma 0.5 0.0

(a) Write the equation of the estimated regression line of y on x for the treatment group and the control group, and the equation of the estimated regression line of y on x for the control group.

(b) Graph with pen on paper the two regression lines, assuming the values of x fall in the range (0, 10). On this graph also include a scatterplot of data (using open circles for treated units and dots for controls) that are consistent with the fitted model.