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What method to validate?

Discussion in 'Capability - Process, Machine, Gage …' started by Chris Glover, May 24, 2017.

  1. Chris Glover

    Chris Glover Active Member

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    We have a piece of equipment that will "kick-out" parts that fail..there is a load displacement spec measure by an LVDT.

    We are trying to validate that the test works as designed.
    30 (No Good) pieces were ran..and the data collected (the "measurements from the LVDT)

    I was not part of the test..just given the data and ask to provide a statistical study showing the equipment did what it was supposed to do (i did..it rejected all 30 parts..but someone was some stats to back it up)
    What would be the best test or method using this data?
     
  2. Bev D

    Bev D Moderator Staff Member

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    When given data from a flawed study design all you can do is tell the requester what his experiment died from...
    This study design doesn't give you any stats. If you tested 30 'bad' parts and it rejected them all then you only get a number: 100%
    In order to do any statistical analysis you need to have 'good' parts as well. Then you can do a cross tab with mcnemer's test or the less powerful kappa statistic.

    When using automatic testers it is important to understand both false rejections and false accepatances...
     
  3. Chris Glover

    Chris Glover Active Member

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    As I dug into this a bit deeper I found that only parts that were above the limits were tested - no acceptable parts not parts below the limits were used...
    This is what happens when you let engineers test their own processes...
     
    Candi1024 likes this.

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