A machine produces drive shafts. Manufacturing currently takes samples of 10 shafts every half an hour to check if the process is in control. Control limits have been set at ± 3 standard deviations of the sample means and are set at 10 ± 3×0.001 cm. A suggestion calls for control limits to be tightened to ± 2 standard deviations, i.e., 10± 2×0.001 cm. As a result the proportion of shafts produced that are defective (outside specification limits) will
A)Increase
B)Decrease
C)Remain unchanged

Question

Quizplus · Accepted Answer

Decreasing control limits increases the number of investigations to check whether the process is still behaving according to its distribution. This does not imply anything about meeting customer specification limits; we will simply be investigating more frequently.[As a second order effect, one can argue that a possible process change - getting out of control - is detected earlier, and hence, fewer defects would be produced.]

A Machine Produces Drive Shafts