Preparation method in Exercise 13-12. Use α = 0.05.

(a) Apply Fisher€™s LSD method with α = 0.05 and determine which levels of the factor differ.

(b) Use the graphical method to compare means described in this section and compare your conclusions to those from Fisher€™s LSD method.

Exercise 13-12

An article in the Materials Research Bulletin [1991, Vol. 26(11)] investigated four different methods of preparing the superconducting compound PbMo₆S₈. The authors contend that the presence of oxygen during the preparation process affects the material€™s superconducting transition temperature T_c. Preparation methods 1 and 2 use techniques that are designed to eliminate the presence of oxygen, and methods 3 and 4 allow oxygen to be present. Five observations on T_c (in °K) were made for each method, and the results are as follows:

Transition Temperature T_(K) 14.8 14.8 14.7 14.8 14.9 Preparation Method 1 2 3 4 14.6 15.0 14.9 14.8 14.7 12.7 11.6 12.4 12.7 14.2 14.4 12.2 12.1 14.4 11.7