In an experiment to determine the factors affecting tensile strength in steel plates, the tensile strength (in kg/mm2), the manganese content (in parts per thousand), and the thickness (in mm) were measured for a sample of 20 plates.
(a) Find the estimated regression model.
(b) Explain the meaning of the estimated regression coefficients. (c) Find and interpret the coefficient of multiple determination. (d) At 5% level, test the validity of the regression model.
(e) At 5% level, test whether any of the two predictors could be dropped from the regression model. (f) Predict the strength for a specimen that is 10 mm thick and contains 8.2 ppt manganese.
(g) Predict with 90% confidence the expected strength for specimens that are 10 mm thick and contain 8.2 ppt manganese.
(h) Predict with 90% confidence the strength for a specimen that is 10 mm thick and contains 8.2 ppt manganese.