TABLE 17-4
A factory supervisor is concerned that the time it takes workers to complete an important production task (measured in seconds) is too erratic and adversely affects expected profits. The supervisor proceeds by randomly sampling 5 individuals per hour for a period of 10 hours. The sample mean and range for each hour are listed below.

She also decides that lower and upper specification limit for the critical-to-quality variable should be 10 and 30 seconds, respectively.
-Referring to Table 17-4, suppose the sample mean and range data were based on 6 observations per hour instead of 5. How would this change affect the lower and upper control limits of an R chart?
A) LCL would increase; UCL would decrease.
B) LCL would remain the same; UCL would decrease.
C) Both LCL and UCL would remain the same.
D) LCL would decrease; UCL would increase.

Question

TABLE 17-4
A factory supervisor is concerned that the time it takes workers to complete an important production task (measured in seconds) is too erratic and adversely affects expected profits. The supervisor proceeds by randomly sampling 5 individuals per hour for a period of 10 hours. The sample mean and range for each hour are listed below.
  
She also decides that lower and upper specification limit for the critical-to-quality variable should be 10 and 30 seconds, respectively.
-Referring to Table 17-4, suppose the sample mean and range data were based on 6 observations per hour instead of 5. How would this change affect the lower and upper control limits of an R chart?
A) LCL would increase; UCL would decrease. 
B) LCL would remain the same; UCL would decrease. 
C) Both LCL and UCL would remain the same. 
D) LCL would decrease; UCL would increase.

Quizplus · Accepted Answer

Increasing the sample size from 5 to 6 observations per hour would decrease the upper control limit (UCL) of an R chart because the control limits are inversely related to the square root of the sample size. The lower control limit (LCL) would remain the same because it is typically zero for an R chart.

TABLE 17-4 A Factory Supervisor Is Concerned That the Time It Takes