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Step 1: Determine whether the process mean is in control
The Moving Average chart plots the unweighted moving average over time. The plotted points can be either moving averages of individual observations or moving averages of subgroup means. Moving averages are calculated from artificial subgroups that are created from consecutive observations. The center line is the process average. The control limits, which are set at a distance of 3 standard deviations above and below the center line, show the amount of variation that is expected in the observations.
Red points indicate points that are more than 3 standard deviations above or below the center line. If the chart shows out-of-control points, investigate those points. Out-of-control points can influence the estimation of process parameters and result in control limits that do not truly represent your process. If you have out-of-control points that are due to special causes, consider omitting these points from the calculations. For more information, go to Specify how to estimate the parameters for Moving Average Chart.
In these results, nine points are out of control on the Moving Average chart. The process is not stable over time. When you hold the pointer over a red point, you can get more information about this subgroup.
Step 2: Identify which points failed the test
Investigate any subgroups that failed the test for special causes. Minitab conducts Test 1, which detects points that fall outside of the control limits. The output shows exactly which points fail the test.
