37. Numerous factors contribute to the smooth running of an electric motor (“Increasing Market Share Through Improved Product and Process Design: An Experimental Approach,”

Quality Engineering, 1991: 361–369). In particular, it is desirable to keep motor noise and vibration to a minimum.

To study the effect that the brand of bearing has on motor vibration, five different motor bearing brands were examined by installing each type of bearing on different random samples of six motors. The amount of motor vibration (measured in microns) was recorded when each of the 30 motors was running. The data for this study follows. State and test the relevant hypotheses at significance level .05, and then carry out a multiple comparisons analysis if appropriate.

Mean Brand 1 13.1 15.0 14.0 14.4 14.0 11.6 13.68 Brand 2 16.3 15.7 17.2 14.9 14.4 17.2 15.95 Brand 3 13.7 13.9 12.4 13.8 14.9 13.3 13.67 Brand 4 15.7 13.7 14.4 16.0 13.9 14.7 14.73 Brand 5 13.5 13.4 13.2 12.7 13.4 12.3 13.08