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.

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 ijk = + i + j + ij, and the residuals are xijk - ijk, Verify that the residuals are .23, - .87, .63, 4.50, - 1.20, - 3.30, -2.03, 1.97, .07, 21.10, 2.30, 1.40, .67, 21.23, .57, 23.43, 2.13, and 3.57.
e. Construct a normal probability plot from the residuals given in part (d). Do the εijk's appear to be normally distributed?

Speed 70 189.7 188.6 190.1 185.1 179.4 177.3 1 189.0 193.0 191.1 0 Formulation 165.1 165.9 167.6 161.7 163.3 159.8 166.6 161.6 170.3 2