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Practical Quality Engineering Resources Statistical Alchemy 2016-01-20

Discussion of some popular methods that have ruined the quality profession

  1. Bev D

    Bev D Moderator Staff Member

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    Bev D submitted a new resource:

    Statistical Alchemy - Discussion of some popular methods that have ruined the quality profession

    Read more about this resource...
     
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  2. Ravi Khare

    Ravi Khare Member

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    Hi Bev,

    You have listed the following methods as amounting to Statistical Alchemy. I concur with you on most; haven't understood well about on a few.

    The RPN value- You have explained very well in your note posted here as a resource. Very well taken.

    Process Capability Indices- Again your note on Process Capability Indices explains it very well.

    Measurement error as a percentage of tolerance (<10% is acceptable)- I do agree that the 10% number may have been conjured up from nowhere. What would be really wrong in comparing the % Error with the Tolerance? To me it would give an idea of the suitability of the measurement system to measure a tolerance I have in mind when I go out to procure one. Even if I decide to leave statistics out, the quantum of error would also help me compare Measurement methods I need to choose between.

    p< 0.05- again the 5% can be argued as arbitrary, though statistics tables have been printed with alpha=0.05 from times before I was born :), what would be wrong on banking upon p values? I have read Wheeler's texts that are skeptical about estimating how distributions behave under the tails, and have read a bit about Deming's views on Normality of distributions. I have heard too that Fisher didn't really subscribe to the concepts of alternate hypothesis to put it mildly. I would love to read your insights into this. I may have missed something you have already explained in other posts or resources about this.

    Fishbone diagrams- After studying and practicing FMEA for a while, I do believe that cause-and-effect relationships do not exist as represented by the fishbone diagram. I believe that Many Causes singly or multiply lead to a Failure Mode, and once the Failure occurs all the consequent Effects of the failure mode are possible. So it's really a Many Causes-Failure Mode-Many Effects relationship; each effect differently serious than other.
    I'm sure you have more than this in mind. Would be eager to read about it.

    Thanks

    Ravi
     
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  3. Eric Twiname

    Eric Twiname Well-Known Member

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    Just wanted to say "Thanks!" and give an anecdote if any find it amusing.

    I love the term "Statistical Alchemy" and it reminds me of a book I found in a used book store in grad school.
    Funds were short, but I had to get it and put it prominently on my shelf where my advisors could see it.

    "Statistical Manipulation of Data" ... I never opened it, but its presence led to some interesting discussions...:)
     
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  4. Bev D

    Bev D Moderator Staff Member

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    Ravi - I haven't yet published on the last 3 topics, but intend to in the coming months. I will post a general notice in the forum once I do publish these...

    you can get a head start on the fishbone diagram thing by reading my ASQ presentation on "A Scientific Approach to Determining Root Cause"
     
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  5. ncwalker

    ncwalker Well-Known Member

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    But.... but .... my bosses all WANT fishbone diagrams. They insist that they are necessary ...... :oops:
     
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  6. Bev D

    Bev D Moderator Staff Member

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    ah but only because you haven't shown them a better way.
     
  7. Eric Twiname

    Eric Twiname Well-Known Member

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    Old dog...new trick....we all know how it can go...
    One man's "fact" is just an opinion in a crowd.

    My mind is made up. Don’t confuse me with the facts - Attributed to Roy Durstine-
     
  8. ncwalker

    ncwalker Well-Known Member

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    I am not known in the real world for my diplomacy. Perhaps that is why I cannot always convince people.
     
  9. ncwalker

    ncwalker Well-Known Member

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    That said, please enjoy my poignant graphic. I don't know the source, unfortunately, but it is fantastic.
     

    Attached File(s): 1. Scan for viruses before using. 2. Report any 'bad' files by reporting this post. 3. Use at your own Risk.:

  10. Candi1024

    Candi1024 Well-Known Member

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    Nice graphic. You.must.assimilate.........
     

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