Hoffman, Jabaay, and Leuer did a study of pencil lead strength. They loaded pieces of lead of the same diameter (supported on two ends) in their centers and recorded the forces at which they failed. Part of their data are given here (in grams of load applied at failure). 4H Lead:56.7, 63.8, 56.7, 63.8, 49.6
H Lead:99.2, 99.2, 92.1, 106.0, 99.2
B Lead: 56.7, 63.8, 70.9, 63.8, 70.9
A) In applying the methods of this chapter in the analysis of these data, what model assumptions must be made? Make three normal plots of these samples on the same set of axes and also make a normal plot of residuals for the one-way model as means of investigating the reasonableness of these assumptions. Comment on the plots.
B) Compute a pooled estimate of variance based on these three samples. What is the corresponding value of sp?