05-20-2016 11:56 AM
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:
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).
05-20-2016 01:34 PM
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."
05-20-2016 02:18 PM
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:
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. : )
05-20-2016 03:07 PM - edited 05-20-2016 03:16 PM
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:
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?
05-20-2016 03:16 PM