TABLE 14-4
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.
-It is not possible for the chart to be out of control when the R chart is in control.

Question

TABLE 14-4
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.
-It is not possible for the  chart to be out of control when the R chart is in control.

Quizplus · Accepted Answer

The statement is incorrect. While the R chart being in control is a necessary condition for the 11ea3200_1dc1_5694_bd9a_a7fe3882ea11_TB2694_11 chart to be in control, it is not sufficient. Other criteria, such as the absence of non-random patterns in the data, must also be met before concluding that the process is in control. Therefore, the 11ea3200_1dc1_5694_bd9a_a7fe3882ea11_TB2694_11 chart can still be out of control even if the R chart is in control.

TABLE 14-4 A Factory Supervisor Is Concerned That the Time It Takes