Plots of sample ranges indicate that the most recent value is below the lower control limit. What course of action would you recommend?

A) Since there is no obvious pattern in the measurements, variability is in control.
B) One value outside the control limits is insufficient to warrant any action.
C) Lower than expected dispersion is a desirable condition; there is no reason to investigate.
D) The process is out of control; reject the last units produced.
E) Variation is not in control; investigate what created this condition.

A value below the lower control limit indicates that the process is exhibiting excessive variability. Therefore, it is best to investigate what is causing this condition and take corrective action. Option A is incorrect because just because there is no obvious pattern does not mean that the variability is in control. Option B is incorrect because even one value outside the control limits indicates that the process is out of control. Option C is incorrect because lower-than-expected dispersion is not desirable if it indicates out-of-control variability. Option D is incorrect because one single data point is not enough to justify rejecting all units produced.