a. Fit regression model (8.2 ). Plowthe fitted regression function and the data . Does the quadratic regression function appear to be a good fit here ? Find R7 . .. . b. Test whether or not there is a regression relation; use alpha - .01. State the alternatives , decision rule , and conclusion . What is the P-value of the test ? c. Obtain joint interval estimates for the mean steroid level of females aged 10, 15 . and 20 respectively . Use the most efficient simulillpeous estimation procedure and a 99 perce ~ family confidence coefficient . Interpret your intervals . d. Predict the steroid levels of females aged IS using a 98 percent prediction interval . Interpret your interval . e. Test whether the quadratic term can be dropped from the model; use a = _01. State the alternatives , decision mile , and conclusion F. Express the fitted regression function obtained in part (a) in terms ofthe original variable X. 8.7 . Refer to Steroid level Problem 8.6. a. Obtain the residuals and plot them against the fitted values and against x on separate graphs Also prepare a normal probability plot . What do your plots show ? b. Test formally for lack of fit. Control the risk of a Type I error at.01. State the alternatives, decision rule , and conclusion . What assumptions did you make implicitly in this test