100% Inspection - 80% Accurate - Quote from Juran (?)

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Rick Goodson

#91
SteelMaiden,

I am not sure which is the best way. Maybe we could perform a DOE to determine which process (half-blind versus half a##ed) produces the best results.

As an aside, what part of NC? I use to work in Albemarle for a couple of years.
 
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J

JMitchell

#93
100% inspection calculation

Originally posted by Kevin Mader
RCW,

Dr. Juran noted that inspection was at best, 80% accurate. Others have guessed less, but that doesn't really matter. Think of it this was. One inspector is .8 in 1 chance likely to find a problem. The second inspector has the same chance. However, if you take .8 and multiply it by .8 (the second inspector), your outcome is .64. With the second inspector, your odds are reduced thus making 200% inspection 64% likely to find a defect.

Dr. Deming offered this in regards 200% inspection: Inspector 1 thinks inspector 2 will catch the defect while inspector 2 thinks inspector 1 will catch it. Net result: nobody inspecting.

I hope this helps.

Kevin
I think that a better way to do this calculation is to say that there is a 20% chance a defect will not be caught. Thus, if you add a second inspection, the chance that a defect will not be caught is 0.20 * 0.20, or 4%. Thus, double inspection is 96% effective, and triple inspection is 99.2% effective, statitically speaking. It doesn't make sense that inspecting more decreases your chance of catching a defect using normal statistical analysis.

However, the situation where an inspector knows that someone else is also inspecting the product may be another beast all together. It may be that when this situation occurs, 100% inspection is only 50% effective - no way to know unless you conduct your own experiment!
 
E

energy

#94
Re: 100% inspection calculation

Originally posted by JMitchell

However, the situation where an inspector knows that someone else is also inspecting the product may be another beast all together. It may be that when this situation occurs, 100% inspection is only 50% effective - no way to know unless you conduct your own experiment!
Why don't we ask the Inspectors. I, for one, would never not inspect because someone else has already inspected. It's absurd. Make the same mistake? Possible. Particularly, if the drawing is unclear or subject to interpretation. That's happened. Supplier, Code Inspector, Source Inspector, Assemblers all missed a very important attribute in my previous life. They changed their drawing practices, not blame Inspectors. I've posted on this before and feel very strongly that no self respecting Inspector would do such a despicable thing such as not do his/her job. It does make a good subject for those professionals who have never sat at an Inspector's bench and performed such an important high pressure task. Inspectors Rule!:ko: :smokin:
 
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