Changing Windows

[Kromkowski@aol.com]

First, the data didn't translate well.  Although, I did sort it out.

Second, there seems to be missing information.  (Or maybe not.)  Namely, all 
of the other times that pilot and copilot visually inspected after a change 
and saw nothing wrong.  Although, number 4 seems to be such a time.  If this 
is a record of every time an inspection is made then, it would seem to 
suggest that rather predictably there is going to be something wrong with the 
change.

Third, although I have stooped to the "gotcha" (most recently reprinting "the 
11 welders" in disguised form), what charts did you use?  There is an 
argument for either using a C-chart or an IndX/MR.  The results won't be too 
different in this case.  Are there signals for special causes? Well, that 
might depend on how you round.  What troubles me is the systemic causes for 
the variation from inspection to inspection.  What kind of system is it, if 
it would not be unusual to find 1 (without rounding and maybe 2 if you round 
and use a C-chart) problem(s) that might lead to injury!  If you round with a 
C-chart, you might also conclude that there is nothing particularly "special" 
about inspection revealing an Unsafe or Unfit for Use situation!

Fourth, as to Deming and small number of samples. You use the words "rare 
occurrences", but, I presume what you mean is that there are only 15 data 
opportunities. I have a recollection that Shewhart liked have 35 points, but 
we see that as with the red beads -- less may suffice.  (At p. 110, OOTC, he 
calculated limits with only six!)  Nine in the example contributed by 
Sherkenbach at p. 112, OOTC.  He used only 11, in the welder example. And 4, 
depending on how you count, on the issue of faulty inspection, at p. 264.

JDKromkowski

PS, below is data in different format.

 #,Insp,TDfcts,D1,D2,D3,D4,D5,D6,D7
 1,A, 9, 1, 0, 1, 0, 2, 4, 1
 2,A,10, 1, 0, 1, 2, 2, 4, 0
 3,B, 1, 0, 0, 0, 0, 0, 1, 0
 4,B, 0, 0, 0, 0, 0, 0, 0, 0
 5,C, 2, 0, 0, 1, 0, 0, 1, 0
 6,B, 1, 0, 0, 0, 0, 0, 1, 0
 7,D, 1, 0, 0, 0, 0, 1, 0, 0
 8,B, 3, 0, 0, 0, 0, 0, 3, 0
 9,A, 2, 0, 0, 0, 0, 0, 2, 0
10,E, 1, 0, 0, 0, 0, 1, 0, 0
11,F, 5, 0, 0, 0, 0, 4, 1, 0
12,A, 7, 2, 0, 0, 0, 2, 3, 0
13,G, 5, 0, 0, 2, 0, 3, 0, 0
14,H, 2, 0, 1, 0, 0, 0, 1, 0
15,A, 4, 0, 0, 0, 0, 2, 2, 0
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