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How many defects are escaping?

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  • #38516

    Nova
    Participant

    Hello,
    Does anyone know some stats from reputable sources on the number of defects that are likely to escape to the customer, based on the number of defects detected through traditional inspection methods?  There is one possible defect per unit, and only one inspector.  I.e. if an inspector finds 10 defective units out of 1000 units produced, how many more defective units are likely to have escaped to the customer?  This assumes that the inspector is not 100% effective.  Not sure what a reasonable effectiveness would be… 80%??
    Any tips would be appreciated…
     

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    #115257

    Tim F
    Member

    I don’t think there is a “typicaL” value to quote here, because it would depend on too many variables — particularly how tough the defects are to spot and how well-trained & well-motivated the inspectors are.IMHO, the only real answer would be to inspect the inspectors. Have random checks of the products AFTER the inspectors have already done their inspections, hopefully by someone better-trained and better-motivated than the standard inspectors. Or add “tagged” defects to the lots and see how many of them are found by the inspectors.(Of course, then you run into problems like the airport baggage inspectors who “lost” the practice luggage with actual bomb-making materials inside!)
    Tim F

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    #115737

    Stan Alekman
    Member

    With historical information about sample sizes and number of defects observed in the sample size, one can calculate and draw the Operational Characteristic curve and learn about the probabilities of detecting batches with different defect contents.

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    #115747

    Vane
    Member

    I have done many capability studies for inspection (cappa) and  most of the operator just detect the 75% or 80% of the failures. But I would could be reduce if you have other inspections points for detection. You can do the Cappa for your inspection.

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