Reaction to an Out-of-Control Signal (Control Chart)

Reaction to an Out-of-Control Signal

•It is very important to investigate every signal of special-cause variation
–Without attention to the charts, those responsible will begin ignoring the signals
•Necessary to have a planned approach
–Verify that data is correct and has been entered correctly
–Determine if a simple explanation of special cause is available (e.g. parts were dropped)
–Verify process change by taking a bigger sample (>20). Use proper sample size to detect critical difference.
–If process change is real, assess process impact to determine next courses of action:
•Line shut down
•Root cause investigation

Out of control signals:

1)Main Indicators
•any point outside of a control limit

2)Secondary Indicators
•any non-random pattern of points on a control chart
–shift or run
–trend
–stratification
–mixture
–periodicity