Process Screen, 1 value per subset, how is within sigma calculated?

tova

Hi,

 

I have data that consists of groups of subgroups.  Each subgroup consists of one value.  When I run the process screening on it, I get an overall sigma (the sigma between the different subgroups) and a within sigma.  I cannot figure out what this within sigma is.  I would like to use the stability index in my analysis, but cannot figure out how it (or the stability ratio) is calculated.  Where does this within sigma come from/how is it calculated?

 

For some reason i can not upload the process screening or the data table.  I have them availableif they are necessary for answering my question.

 

Thanks,

 

Tova

vince_faller

Minimum subgroup size is two.  If you run. 

 

names default to here(1);<BR />dt = open("$SAMPLE_DATA\Consumer Prices.jmp");
dt << Process Screening(
	Y( :Price ),
	Grouping( :Series ),
	Control Chart Type( "Indiv and MR" ),
	Time( :Date ),
	Subgroup Sample Size( 1 )// this can't happen
);

You should get a warning in log saying 

Minimum subgroup size is 2.

If you do this via the GUI then it should actually give you a popup.

If you take your process screening and save to script window I'm guessing it overwrote your Subgroup Sample Size( 1 ) with a 2.  

 

Even if you give it a subgroup column, it should do this.