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Process Screening on I-MR, control limits from within stdev?

Simple question.  Just curious if the within stdev on the IMR version is used for limits (in the absence of a specified sigma).  I'm 99% sure they are, just wanted to confirm, and didn't see this in the process screening report notes.

AnalyticsRe: Process Screening on I-MR, control limits from within stdev?

If you use the Control Chart Type specification of Indiv and MR in Process Screening, the limits will be calculated using within sigma (average(moving ranges)/d2(n)) the same as Control Chart Builder does.  You can find the calculations here:

https://www.jmp.com/support/help/en/15.2/#page/jmp/control-limits-for-individual-measurement-and-moving-range-charts.shtml#ww1157183

Re: Process Screening on I-MR, control limits from within stdev?

Thanks Tonya, I was 99% sure that was the case but wanted to confirm.  

 

One small other thing I noticed, though I would mention since I have you. Kind of an interesting blip.   The Cp in Process Screening uses the within sigma, even if there is a specified sigma, however if you punt to the control chart platform from the Process Screening tool the Cp will use the specified sigma instead of the within.

Re: Process Screening on I-MR, control limits from within stdev?

Please send an example of Cp not matching between Process Screening and Control Chart Builder.  I ran the following code and got them to match.

dt=Open("$Sample_Data/Cities.jmp");
dtLimits=New Table( "My Limits",
 Add Rows( 13 ),
 New Column( "Process",
  Character,
  "Nominal",
  Set Values(
   {"OZONE", "NO", "OZONE", "OZONE", "OZONE", "OZONE", "OZONE", "NO", "NO",
   "NO", "NO", "NO", "NO"}
  )
 ),
 New Column( "LSL",
  Numeric,
  "Continuous",
  Format( "Best", 12 ),
  Set Values(
   [0.1, 0.02, 0.2, 0.1, 0.1, 0.1, 0.1, 0.02, 0.02, 0.02, 0.02, 0.02, 0.02]
  )
 ),
 New Column( "Target",
  Numeric,
  "Continuous",
  Format( "Best", 12 ),
  Set Values(
   [0.2, 0.04, 0.3, 0.2, 0.2, 0.2, 0.2, 0.04, 0.04, 0.04, 0.04, 0.04, 0.04]
  )
 ),
 New Column( "USL",
  Numeric,
  "Continuous",
  Format( "Best", 12 ),
  Set Values(
   [0.3, 0.06, 0.4, 0.3, 0.3, 0.3, 0.3, 0.06, 0.06, 0.06, 0.06, 0.06, 0.06]
  )
 ),
 New Column( "Grouping",
  Character,
  "Nominal",
  Set Values(
   {"C", "C", "MW", "N", "S", "TX", "W", "C", "MW", "N", "S", "TX", "W"}
  )
 ),
 New Column( "Center",
  Numeric,
  "Continuous",
  Format( "Best", 12 ),
  Set Values(
   [0.2, 0.04, 0.15, 0.16, 0.13, 0.2, 0.12, 0.04, 0.026, 0.035, 0.026,
   0.025, 0.02]
  )
 ),
 New Column( "Sigma",
  Numeric,
  "Continuous",
  Format( "Best", 12 ),
  Set Values(
   [0.05, 0.01, 0.05, 0.04, 0.06, 0.05, 0.05, 0.01, 0.01, 0.01, 0.02, 0.03,
   0.01]
  )
 ),
 New Column( "Importance",
  Numeric,
  "Continuous",
  Format( "Best", 12 ),
  Set Values( [1, 4, 1, 2, 2, 3, 3, 4, 5, 5, 6, 6, 7] )
 ),
 Set Label Columns( :Process )
);

obj=dt<<PROCESS screening=""></PROCESS>

See attached image.

Re: Process Screening on I-MR, control limits from within stdev?

Tonya

 

Aha! I figured it out.  Very interesting, it bothered me because we had nearly identical scripts.

Here's the trick.  Don't specify sigma for 100% of your variables.  If you have a couple process variables without a specified sigma, it will use the within for ALL of your variables in process screening.  Which makes some sense from a programming perspective as I'm guessing the calculations are happening on the columns, so the specified sigma has some/any nulls in it it defaults to the within column.

 

Here, I removed the specified sigma for a few of your variables in the script you provided.  But the one that makes the control chart does still have a specified sigma, so what shows up in the control chart is different than what is in Process Screening:

 

dt=Open("$Sample_Data/Cities.jmp");
dtLimits=New Table( "My Limits",
 Add Rows( 13 ),
 New Column( "Process",
  Character,
  "Nominal",
  Set Values(
   {"OZONE", "NO", "OZONE", "OZONE", "OZONE", "OZONE", "OZONE", "NO", "NO",
   "NO", "NO", "NO", "NO"}
  )
 ),
 New Column( "LSL",
  Numeric,
  "Continuous",
  Format( "Best", 12 ),
  Set Values(
   [0.1, 0.02, 0.2, 0.1, 0.1, 0.1, 0.1, 0.02, 0.02, 0.02, 0.02, 0.02, 0.02]
  )
 ),
 New Column( "Target",
  Numeric,
  "Continuous",
  Format( "Best", 12 ),
  Set Values(
   [0.2, 0.04, 0.3, 0.2, 0.2, 0.2, 0.2, 0.04, 0.04, 0.04, 0.04, 0.04, 0.04]
  )
 ),
 New Column( "USL",
  Numeric,
  "Continuous",
  Format( "Best", 12 ),
  Set Values(
   [0.3, 0.06, 0.4, 0.3, 0.3, 0.3, 0.3, 0.06, 0.06, 0.06, 0.06, 0.06, 0.06]
  )
 ),
 New Column( "Grouping",
  Character,
  "Nominal",
  Set Values(
   {"C", "C", "MW", "N", "S", "TX", "W", "C", "MW", "N", "S", "TX", "W"}
  )
 ),
 New Column( "Center",
  Numeric,
  "Continuous",
  Format( "Best", 12 ),
  Set Values(
   [0.2, 0.04, 0.15, 0.16, 0.13, 0.2, 0.12, 0.04, 0.026, 0.035, 0.026,
   0.025, 0.02]
  )
 ),
 New Column( "Sigma",
  Numeric,
  "Continuous",
  Format( "Best", 12 ),
  Set Values(
   [0.05, 0.01, 0.05, 0.04, 0.06, 0.05, 0.05, 0.01, 0.01, 0.01]
  )
 ),
 New Column( "Importance",
  Numeric,
  "Continuous",
  Format( "Best", 12 ),
  Set Values( [1, 4, 1, 2, 2, 3, 3, 4, 5, 5, 6, 6, 7] )
 ),
 Set Label Columns( :Process )
);

obj=dt<<PROCESS screening=""></PROCESS>