Certified Production & Operations Manager (POM) Practice Exam

If sample ranges indicate that the most recent value is below the lower control limit, what action should be taken?

1. Nothing, it's a natural variation

2. Immediately accept the lot as defective

3. Investigate the cause of the variation

4. Continue with the current process

The correct answer is: Investigate the cause of the variation

The most appropriate action when a sample range indicates that the most recent value is below the lower control limit is to investigate the cause of the variation. Control limits are established based on historical process data to define the acceptable range of variation for a process. When a value falls outside these limits, it suggests that something unusual is occurring, which may indicate a potential issue that could affect product quality. Investigating the cause allows for the identification of whether the variation is due to a special cause—something that is not typical of the process, such as equipment malfunction or human error—or if it truly is part of the natural variation expected from the process. Addressing special causes can prevent defective products from being produced and ensure that the process is back within control limits. Choosing to do nothing assumes the variation is simply random or natural, which risks quality issues. Accepting the lot as defective without investigation could lead to unnecessary losses or missed opportunities to correct underlying problems. Continuing with the current process without investigation could perpetuate the issue and result in more significant quality failures down the line. Thus, thorough investigation is crucial to maintain process integrity and quality assurance.