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Quentin
Super User

Hi,

 

I'm looking for a published example (online or in the docs) of data and results from running an S chart (i.e. control chart for within group standard deviations), where the group size varies. 

 

I see an example of this for an XRChart:

http://support.sas.com/documentation/onlinedoc/qc/ex_code/141/shwmns.html

 

But I want an SChart (or XSCHART), using the default method used by SAS (ASTM 1976).

 

Goal is to find some published data to use in a validation report.  Would appreciate any suggestions.  (I'm going to try and buy the ASTM book, but hoping to find something online faster than snail mail).

 

Thanks,

--Q.

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Rick_SAS
SAS Super FREQ

Not sure what "ASTM 1976" means, but have you seen the chapter "Analyzing Quality Data with SAS", which includes an XSCHART example on p 9?

 

The excerpt is from Rutledge  Just enough SAS: A Quick-Start Guide to SAS for Engineers. The  data are available from the book web page.. Just click "Example Code and Data."

Quentin
Super User

Thanks Rick, I hadn't seen that book.

 

Unfortunately, I'm looking for an example of an S chart (or XSCHART) where the subgroup size varies, so the process limits on the S chart will also vary accordingly. 

 

For example, this:

 

data have;
  do lot=1 to 20;
    do n=1 to floor(ranuni(3)*20); *random number of values in each group;
      y=100+sqrt(10)*rannor(3);
      output;
    end;
  end;
run;

proc shewhart data=have;
  xschart y*lot;
run;

Produces a chart like:

 

XSChart.png

 

By "ASTM 1976" was referring to the reference for the calculation in th docs:

American Society for Testing and Materials (1976), ASTM Manual on Presentation of Data and

Control Chart Analysis, 1916 Race Street, Philadelphia, PA 19103.

 

Amazon is selling it for $5, so hopefully I'll be lucky when it arrives. : )

BASUG is hosting free webinars Next up: Mark Keintz presenting History Carried Forward, Future Carried Back: Mixing Time Series of Differing Frequencies on May 8. Register now at the Boston Area SAS Users Group event page: https://www.basug.org/events.
Rick_SAS
SAS Super FREQ

If you go to Google and search in "Images" for

shewhart x chart unequal sample size

you will see many examples.  I'm not sure whether these qualify as "published examples."

For example, one instance is a set of course notes:

http://www.math.montana.edu/jobo/st528/documents/chap6b.pdf (p 68-69)

 

If you need a published example of high importance, you can find example data and chart on pp 244-248 of

Introduction to Statistical Quality Control by Douglas C. Montgomery, 4th Ed.

Do the results have to be created by SAS?

Quentin
Super User
Thanks again Rick. I've got Montgomery 2nd Ed open on my desk, but it looks to me like the example has a couple errors, and I don't think it's using the same method as SAS. I should probably get the latest edition. Seems like Montgomery is a standard text for this stuff. No, I don't need it to be created by SAS. And in a validation sense, arguably better if the truth I use is not from SAS.
BASUG is hosting free webinars Next up: Mark Keintz presenting History Carried Forward, Future Carried Back: Mixing Time Series of Differing Frequencies on May 8. Register now at the Boston Area SAS Users Group event page: https://www.basug.org/events.

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