The accompanying Minitab output resulted from applying both the backward elimination method and the forward selection method to the wood specific gravity data given in Exercise 49. Explain for each method what occurred at every iteration of the algorithm.
The article “Anatomical Factors Influencing Wood Specific Gravity of Slash Pines and the Implications for the Development of a High-Quality Pulpwood” (TAPPI, 1964: 401–404) reported the results of an experiment in which 20 specimens of slash pine wood were analyzed. A primary objective was to relate wood specific gravity (y) to various other wood characteristics. Consider the accompanying data (top of page 570) on y and the predictors 1 number of fibers/mm2 in springwood, 2 number of fibers/mm2 in summerwood, 3 springwood %, 4 % springwood light absorption, and 5 % summerwood light absorption. Based on the accompanying Minitab output, which model(s) would you recommend investigating in more detail?