The accompanying data on y 5 energy output (W) and x = temperature difference (°K) was provided by the authors of the article "Comparison of Energy and Exergy Efficiency for Solar Box and Parabolic Cookers" (J. of Energy Engr., 2007: 53-62). The article's authors fit a cubic regression model to the data. Here is Minitab output from such a fit.conveys information about precision and reliability. Then compare this prediction to the estimate obtained in (c).
a. What proportion of observed variation in energy output can be attributed to the model relationship? b. Fitting a quadratic model to the data results in R2 = .780. Calculate adjusted R2 for this model and compare to adjusted R2 for the cubic model.
c. Does the cubic predictor appear to provide useful information about y over and above that provided by the linear and quadratic predictors? State and test the appropriate hypotheses. d. When x = 30, Sy= .0611. Obtain a 95% CI for true average energy output in this case, and also a 95% PI for a single energy output to be observed when temperature difference is 30.