Refer to the data given in Exercise 12.28. The MINITAB printout is reproduced here.
Regression Analysis: y versus x
The regression equation is
y = -26.8 + 1.26 x

a. What assumptions must be made about the distribution of the random error, ε?
b. What is the best estimate of σ2, the variance of the random error, ε?
c. Use the diagnostic plots for these data to comment on the validity of the regression assumptions.

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Transcribed Image Text:

Predictor Constant Coef -26.82 1.2617 SE Coef 14.76 1.82 0.086 0.1685 7.49 0.000 S -7.61912 R-Sq-75.7 R-Sq(adj ) -74 . 3% Analysis of Variance Source DE MS Regression 1 3254.0 3254.056.05 0.000 Residual Error 18 1044.9 58.1 19 Total 4299.0 Normal Probability Plot of the Residuals (response is y) 80 701TT 50H + + +--A + + + 30 20 10t-ㄧㄧㄧ ㄒ ㄧ 20 10 10 20 Residual Residuals versus the Fitted Values (response is y) 20 10 一10一 20 60 70 80 90 100 Fitted Value