SPC on the rocks (2)*

[David Kerridge <dfkerridge@mac.com>]

Obviously I need to explain myself a bit more clearly. That's the
trouble with writing for the DEN - we have to be so brief that
we leave a lot to the imagination of the reader.

Lets start with some points on which I think we all agree. I hope
to hear if I have oversimplified:

(1)  Understanding variation is one of the foundations of the
       Deming Philosophy.

(2)  If figures are worth collecting, they are worth plotting. If
       they aren't worth collecting, looking at the plot may help
       us see that.

(3)   The best way to understand the Deming Philosophy is to
        practice it. Unfortunately much of it is directed at the
        top management of a company, and so for the rest of us,
        opportuntities to put it into practice are rare. The study
        of variation, on the other hand, is for everyone.

(4)    Whenever possible, we should put "control limits" on our
        plot, to indicate the range of variation which is inevitable,
        given the way the system currently works.

(5)    The plot rarely tells us what to do, in the sense of telling
         us what action will improve the process. What we should
         look for is clues that suggest what to try first. This may be
         the removal of special causes, or action on the system as a
         whole. If it does work, the plot will show us that we have
         succeeded.

In my next post I will move on to points that may be more
controversial.
--
Best wishes

David

dfkerridge@mac.com