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Jun 12, 2019 1:32 AM
(1001 views)

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

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Minimum subgroup size is two. If you run.

`names default to here(1);`

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.

Vince Faller - Predictum

2 REPLIES 2

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Minimum subgroup size is two. If you run.

`names default to here(1);`

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.

Vince Faller - Predictum

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
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Re: Process Screen, 1 value per subset, how is within sigma calculated?

Thank you!!