Suppose that, when setting up the experiment in problem 11.49, the operations manager is able to study the effect of side-to-side aspect in addition to air-jet pressure. Thus, instead of the onefactor completely randomised design in problem 11.49, a twofactor factorial design was used, with the first factor, side-to-side aspect, having two levels (nozzle and opposite) and the second factor, air-jet pressure, having three levels (30 psi, 40 psi and 50 psi). A sample of 18 yarns is randomly assigned, three to each of the six side-to-side aspect and pressure level combinations.

The breaking-strength scores, stored in < YARN >, are as follows

a. At the 0.05 level of significance:

i. is there a significant interaction between side-to-side aspect and air-jet pressure?

ii. is there an effect due to side-to-side aspect?

iii. is there an effect due to air-jet pressure?

b. Plot the mean yarn breaking strength for each level of sideto-side aspect for each level of air-jet pressure.

c. If appropriate, use the Tukey procedure to study differences between the air-jet pressures.

d. On the basis of the results of

(a) to (c), what conclusions can you reach concerning yarn breaking strength? Discuss.

e. Compare your results in

(a) to

(d) with those from the completely randomised design in problem 11.49. Discuss fully.