control chart with data that are already averages

[#1]

Good morning

I am trying to indicate to the quality platform that the data I collect are already averages (of 9-21-49 values depending on the case).

I haven't found where to tell JMP that the table values are already averages. As a result, the calculated limits are wrong compared to what I calculate for my data in Matlab.

Any hint of the correct checkbox?

thanks in advance.

[#2]

Welcome to the community.  I'm a little confused by the question.  Do you have all of the data or only the averages?  If you do not have the complete data set,  it is impossible to calculate the range of the within subgroup variation.  This is required as the average range is used to calculate control limits for both the range chart and the average chart.    Another option is to do an IR chart (Individual moving range). The IR chart is not answering the same question as the X-bar chart.

[#3]

As stated, I only have averages.

I saw the possibilities offered if we had all the data, but that is not my case.

Sincerely

[#4]

When you mentioned the calculated limit not same like in Matlab, what type of method that you used in Matlab to calculate control limit?
If you want a flexible calculation of control limit (depending on your scenario), maybe you can use Control Chart Builder.
If you just want to add a note to state that the column is average, you can define the column properties & add notes that it is an average ( but i doubt it will change the calculation ).
For single data point (in this case “average value”), you can either use IR method or Levey-Jennings in JMP
IR in this case will treat your average as single point & sigma is moving range between the 2 averages.
Levey-Jennings will treat you average as single point as well & sigma is Levey-Jennings (overall standard deviation of all averages).

p/s: Earlier post mentioned Minitab instead of Matlab. Thanks @ih for the correction.

[#5]

I am no expert here but I second the question from @WebDesignesCrow about how this is done in MATLAB.  The variation of individual samples seems like it would be central to subsequent analyses so I suspect there is some assumption made in MATLAB.  Consider the samples data in the example script below.  Using the same averages for each group but different variations within the group, the control limits change significantly.

Run this script to recreate the sample data and charts above:

View more...

Names default to here(1);

Random Reset(84);

dtRaw = New Table( "Raw Data",
	Add Rows( 20 ),
	New Column( "Raw Data",
		Numeric,
		"Continuous",
		Format( "Best", 12 ),
		Formula( Random Normal() )
	),
	New Column( "Group",
		Numeric,
		"Continuous",
		Format( "Best", 12 ),
		Formula( Floor( (Row() - 1) / 4 ) ),
		Set Selected
	)
);

dtRaw << Run Formulas;

dtRaw:Raw Data << Delete Formula;
dtRaw << New Column("0 Variation", Numeric, "Continuous", Format("Best", 12), Formula(Col Mean(:Raw Data, :Group)));
dtRaw << New Column("Mean", Numeric, "Continuous", Format("Best", 12), Formula(Col Mean(:Raw Data, :Group)));
dtRaw << New Column("StDev", Numeric, "Continuous", Format("Best", 12), Formula(Col Std Dev(:Raw Data, :Group)));
dtRaw << New Column("Half Variation", Numeric, "Continuous", Format("Best", 12), Formula((:Raw Data + :Mean) / 2));

dtSum = (tab = dtRaw  << Tabulate(
	Show Control Panel( 0 ),
	Add Table(
		Column Table( Analysis Columns( :Raw Data ), Statistics( Mean ) ),
		Row Table( Grouping Columns( :Group ) )
	)
)) << Make Into Data Table;
tab << Close Window;



New Window("Control Charts",
	vlb = V List Box(
		dtRaw << Control Chart Builder(
			Size( 570, 150 ),
			Variables( Subgroup( :Group ), Y( :Raw Data ) ),
			Show Control Panel( 0 )
		),
		dtRaw << Control Chart Builder(
			Size( 570, 150 ),
			Variables( Subgroup( :Group ), Y( :Half Variation ) ),
			Show Control Panel( 0 )
		),
		dtRaw << Control Chart Builder(
			Size( 570, 150 ),
			Variables( Subgroup( :Group ), Y( :Mean ) ),
			Show Control Panel( 0 )
		),
		dtSum << Control Chart Builder(
			Size( 570, 200 ),
			Variables( Y( :"Mean(Raw Data)"n ) ),
			Show Control Panel( 0 )
		)
	)
);

ob = (vlb << XPath("//OutlineBox[text()='Control Chart Builder']"));
ob[1] << Set Title("Raw (Random) data");
ob[2] << Set Title("Variation cut in half");
ob[3] << Set Title("No variation - average repeated");
ob[4] << Set Title("Individual values as averages");