The above article states that you can add custom tests to control charts, but it appears that this only works when the "Statistics" mode is set to "Average". I'm using "Moving Range on Means" which only offers the test for outside of Control Limits.
Is there a there a way of testing for, say, X points above or below Avg in this mode? I'm probably missing the statistical reason for this!
Custom tests are for location charts only. A Moving Range on Means chart is a dispersion chart. Custom tests are not available for dispersion charts. You would need to create your own via JSL.
There are many papers on the applicability of certain trend rules for dispersion charts.
If you are not comfortable with JSL, create a table of the moving range of means, then use the control chart builder for an Individual chart or a Levey-Jennings chart then select the trend rules recommended for a moving range.
From experience, many who look at a moving range don't realize if there is a shift in the mean that persists, only 1 OOC point, at the point of the shift, will appear on teh control chart. Also, if one mean is unusual then you will get 2 unusual range points: 3 menas that are typical, unusual, typical, the two moving ranges involving the OOC will be unusual. So I understand why JMP does not automatically supply trend rules. However, the trend rule that flags too many points close to the center line, demonstrates a reduction in variability and a trend rule with 10-15 points not within the zones closest to the center line demonstrates an increase in variability ( worse stability).
Is it possible to access the points created in the chart as a list? I'm familar with object orientated programming but I don't believe that JSL language would allow me to do something simiar to the following:
CCB = Control Chart Builder( ... some code to create CCB ); newList = CCB.Points();
To get the points from the Moving Averages chart, you can use the "Save Summaries" message and pass it to the Platform. Below is a simple example of getting the points into a list:
Names Default To Here( 1 ); dt = Open( "$SAMPLE_DATA/Big Class.jmp" ); theccb = dt << Control Chart Builder( invisible, Show Capability( 0 ), Variables( Y( :height ) ), Chart( Position( 1 ), Points( Statistic( "Moving Range" ) ), Limits( Sigma( "Moving Range" ) ) ), Chart( Position( 2 ), Limits( Sigma( "Moving Range" ) ) ) ); ccb = theccb << save summaries; // The values from the Moving Range column(column 3) are numeric // and would be returned as a matrix. Therefore, to convert the // results into a list, the As List() is added. newList = As List( Column( ccb, 3 ) << get values ); close( ccb, nosave ); report( theccb ) << close window;
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