18. The accompanying data resulted from an experiment to investigate whether yield from a certain chemical process depended either on the formulation of a particular input or on mixer speed.

Speed 60 70 80 189.7 185.1 189.0 1 188.6 179.4 193.0 190.1 177.3 191.1 Formulation 165.1 161.7 163.3 2 165.9 159.8 166.6 167.6 161.6 170.3 A statistical computer package gave SS(Form)
2253.44, SS(Speed)
230.81, SS(Form*Speed)
18.58, and SSE
71.87.

a. Does there appear to be interaction between the factors?

b. Does yield appear to depend on either formulation or speed?

c. Calculate estimates of the main effects.

d. The fitted values are xˆijk
ˆ ˆi ˆ

j ˆij, and the residuals are xijk  xˆijk. Verify that the residuals are .23,

.87, .63, 4.50, 1.20, 3.30, 2.03, 1.97, .07, 1.10,

.30, 1.40, .67, 1.23, .57, 3.43, .13, and 3.57.

e. Construct a normal probability plot from the residuals given in part (d). Do the ijk’s appear to be normally distributed?