39. Consider the accompanying data on breaking load

(kg/25-mm width) for various fabrics in both an unabraded condition and an abraded condition

( The Effect of Wet Abrasive Wear on the Tensile Properties of Cotton and Polyester-Cotton Fabrics, J. Testing Eval., 1993: 84—93).

a. Use the paired t test, as did the authors of the cited article, to test H0: mD  0 versus Ha: mD 0 at signi cance level .01.

Fabric 1 2 3 4 5 6 7 8 U 36.4 55.0 51.5 38.7 43.2 48.8 25.6 49.8 A 28.5 20.0 46.0 34.5 36.5 52.5 26.5 46.5

b. Do the assumptions necessary for using the paired t test appear to be plausible? Explain.

c. Delete the observation on fabric 2 and use the paired t test on the remaining observations.

How does your conclusion compare with that of part (a)?