Difference between two Cpk analysis tool

mkhoddam

Hi all,

 

I have generated random data from Johnson Sl distr. and saved it in a column. Now, when I use these two Cpk analysis tolls, I get diff. results:

1. Analyze> Quality and Process> Process capability

2. Analyze> Fit > Capability analysis (I have tried all of the options for long term, moving range, ...)

For both method I chose Johnson Sl distr. and the same USL.

So, how come I get diff. results? Which one is better? 

 

Thanks,

Mona

Georg

Dear Mona,

 

I could not reproduce your Problem, please see the following script, that generates that table,

and the two scripts generate the capability Reports (one via Process Capability, the other via Distribution).

But when running the script more times, all cpk's are different, because the data is newly generated by the Formula behind.

Maybe that's the Problem? You could simply delete the Formula to "fix" the data.

 

Best regards,

   Georg

New Table( "Johnson SI Capability",
	Add Rows( 100 ),
	Compress File When Saved( 1 ),
	New Script(
		"Distribution",
		Distribution( Continuous Distribution( Column( :Johnson SI ) ) )
	),
	New Script(
		"Process Capability",
		Process Capability(
			Process Variables( :Johnson SI ),
			Moving Range Method( Average of Moving Ranges ),
			Individual Detail Reports( 1 ),
			Capability Box Plots( 1 ),
			Goal Plot( 1 ),
			Capability Index Plot( 1 ),
			Process Performance Plot( 0 )
		)
	),
	New Script(
		"Distribution of Johnson SI",
		Distribution(
			Continuous Distribution(
				Column( :Johnson SI ),
				Process Capability( Use Column Property Specs )
			)
		)
	),
	New Column( "Johnson SI",
		Numeric,
		"Continuous",
		Format( "Best", 12 ),
		Formula( Random Johnson Sl( 1, 1, 1 ) ),
		Set Property(
			"Spec Limits",
			{LSL( 1 ), USL( 3 ), Target( 2 ), Show Limits( 1 )}
		),
		Set Selected
	)
);