Programming the statistical procedures from SAS

Limiting INSET to the last set of control limits

Reply
Contributor
Posts: 45

Limiting INSET to the last set of control limits

Hello,

I am working with a manufacturing process data and cannot figure out how to control the inset calculations.  For example:  Lets say I have 80 data results that I am graphing using the Proc Shewhart procedure with an irchart.  But between data point 40 and 41 I split the control limits due to a shift in the mean.  So I have my control limits for data points 1-40 and a second set of control limits for 41-80.  Specification limits for all data is the same.  I then use the inset statement to provide a CPK point estimate along with the 95% confidence interval points.  However, I want the inset statement to only reflect on the data just within the second set of control limits.

SAS Code:

proc shewhart history=data2 limits=stats;

  irchart test*lot_count='*'  / outlabel=(lot_count) nochart2  vref=vref ciindices lsl=&lsl usl=&usl readphases=all
readindexes=all phaselegend vreflabpos=2 zerostd tests=1 to 4 testlabel1=' ' testlabel2=' ' clipfactor=2 totpanels=1;

  inset stddev cpklcl='Cpk 95% Lower' cpk='Cpk' cpkucl='Cpk 95% Upper' / pos=sw format=6.2 opacity=0;

  label &var="&var(&units)";

run;

Where data2 contains the two different _PHASE_ values, and stats data set contains the two sets of control limits with _INDEX_ values to be matched with _PHASE_ values.

And also, how can I do this for a histogram in proc capability.  I want the histogram to include all data points in the chart, but I only want the ppk calculations to be based off only the 2nd half of the data.

Thank you,
Jeff

Trusted Advisor
Posts: 1,188

Re: Limiting INSET to the last set of control limits

Hi,

I don't have an easy answer.  Makes sense that if you have a phased control chart, you would want phased Cpk (or in your case Cpk for just the most recent phase).

Typically I haven't used the graphics from Shewhart much.  I've instead used the proc to compute the data I want (process limits, Cpk, etc) and output them to a dataset, then used GTL to create a custom chart.  It's more work, but gives more control over the final output.  So with that approach, could just run Shewhart a second time using only data from the most recent phase to to get the desired Cpk.

--Q.

Ask a Question
Discussion stats
  • 1 reply
  • 136 views
  • 0 likes
  • 2 in conversation