An article in the Journal of Quality Technology

(Vol. 13, No. 2, 1981, pp. 111–114) describes an experiment that investigates the effects of four bleaching chemicals on pulp brightness. These four chemicals were selected at random from a large population of potential bleaching agents. The data are as follows:

Oven Temperature 1 77.199 74.466 92.746 76.208 82.876 2 80.522 79.306 81.914 80.346 73.385 3 79.417 78.017 91.596 80.802 80.626 4 78.001 78.358 77.544 77.364 77.386

(a) Is there a difference in the chemical types? Use

???? = 0.05.

(b) Estimate the variability due to chemical types.

(c) Estimate the variability due to random error.

(d) Analyze the residuals from this experiment and comment on model adequacy.