Examples of Weighted Moving Average Charts
UWMA Chart Example
In the sample data table Clips1.jmp, the measure of interest is the gap between the ends of manufactured metal clips. To monitor the process for a change in the average gap, subgroup samples of five clips are selected daily. A UWMA chart with a moving average span of three is examined.
1. Select Help > Sample Data Library and open Quality Control/Clips1.jmp.
2. Select Analyze > Quality and Process > Control Chart > UWMA.
3. Select Gap and click Process.
4. Select Sample and click Sample Label.
5. Change the Moving Average Span to 3.
6. Click OK.
The result is the chart in Figure 9.2. The point for the first day is the mean of the five subgroup sample values for that day. The plotted point for the second day is the average of subgroup sample means for the first and second days. The points for the remaining days are the average of subsample means for each day and the two previous days.
The average clip gap appears to be decreasing, but no sample point falls outside the 3σ limits.
Figure 9.2 UWMA Charts for the Clips1 data
