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

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RCW

Quite Involved in Discussions
#1
Quote from Juran (?)

I need some help here.

My registrar told me of a quote from Juran (?) saying that in 100% inspection there is an 80% chance of finding the problem (if it exists). If three people inspect the item and they know that someone else has inspected it, the chance of finding the problem drops to 60%.

Does anybody know if these numbers are correct and where that quote came from, if it was indeed from Juran?

Contrary to what the intro to this forum says, I don't have a copy of Juran's Quality Handbook, mainly because my boss is a penny-pinching cheapskate :mad:, but that's another story.

Thanks!
 

Kevin Mader

One of THE Original Covers!
Administrator
#2
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
 

Jim Biz

Inactive Registered Visitor
#3
I don't have a copy of Juran's Quality Handbook, mainly because my boss is a penny-pinching cheapskate
RCW - can't garuntee anything I'ts been awhile since I looked in my library archives - but I may have a copy you could use.

If yer interested Shoot me an E-mail & I'll look around this evening.
 
A

Al Dyer

Guest
#4
RCW,

I'll sell you my book for $60.00!!!

100% inspection is as bogus as saying my gage does not have wear and shouldn't be calibrated.

If your boss is that cheap you are in trouble. Try this as a test:

1: Take 10 parts that you know are flawed;
2: Employ 3 random employees to measure the parts;
3: Tell the trio that there are 5 good and 5 bad parts;

(if you really want to get sneaky call it an R&R test)

4: Record all off their results and review the data.

Reply back to the forum after you present the results to your boss.
 

Marc

Retired Old Goat
Staff member
Administrator
#5
Re: Quote from Juran (?)

Originally posted by RCW

My registrar told me of a quote from Juran (?) saying that in 100% inspection there is an 80% chance of finding the problem (if it exists). If three people inspect the item and they know that someone else has inspected it, the chance of finding the problem drops to 60%.
Kevin explained the guts, but remember: This is only true for human inspection. A 100% poka yoke (mechanical/electronic/electro-mechanical) 'inspection' is a different animal.

> I don't have a copy of Juran's Quality Handbook, mainly
> because my boss is a penny-pinching cheapskate

You may not like me saying this, but it's worth it to buy it for yourself. For me it's mainly a paperweight now, but if you looked at mine you would see it is well worn, marked up all over and has saved my butt several times. When I sat for my CQE over 10 years ago it was close to a bible for me. To me it is a tool. I wouldn't want one from an employer unless it was agreed it woud be mine to keep. I want it in MY library! :thedeal:
 

Kevin Mader

One of THE Original Covers!
Administrator
#7
I stand corrected. Thanks Marc!;)

Browse ebay for Juran's hanbook. Not too long ago I found a fifth edition copy selling for an opening bid of $60 (oddly enough). There are many great deals there folks for books for a small fraction of what they originally sold for. In addition, you can shop amazon or borders used books. Please read the fine print!! Many copies are in terrific order, others have highlighting and marked pages. I bought a back up copy of Out of the Crisis for $10 including shipping. In all honesty, this is in better condition (still stiff when you open it) than my own copy at home which I paid $60 for.

Happy hunting!!

Kevin
 

RCW

Quite Involved in Discussions
#8
Thanks for all the responses!

Here's a little background info on my original question:

1. Upper management and the sales dept. have always bragged to customers that we only use 100% inspection and no SPC is used here. (We are a small electronics firm that produces small quantities (1 - 10 pieces) of circuit boards, cables or wired panels, so it is hard to justify using SPC for the small quantites).

However, the big-wigs make it sound like 100% "visual" inspection catches everything, which it doesn't.

2. Recently, due to excessive workloads, product has been getting out of here with minor defects (i.e. missing labels, missing i.d. stamping). So the directive from upstairs is that more people have to check the product before it goes out the door. This brought to mind the quote my registrar told me about that adding additional "eyes" to inspection actual reduces the odds of finding errors. That's why I wanted something in writing to show the disbelievers.

3. I'm also planning to use Al's suggestion of the mock R&R study. While your example suggests measuring parts, I'm sure that it can also be applied to visual inspection (i.e. finding missing solder from connections).

4. As far as getting a copy of Juran's book, I'm trying to obtain a copy through an inter-library loan, to examine the book for merit. And no, I'm not insulted by the suggestion that I buy my own copy. It's just that (and I don't mean to step on anybody's toes) I'm an electronic technician and a computer science major who is masquerading as a Quality Manager. Through a bad decision of my own and a raw deal from the then president of the company, I ended up being "the quality department". It's because of this that I can't see dropping my personal money on buying the book.


Much thanks to those out there in this forum for all the help and input received for this lost soul. It warms my heart to find a place where I can find practical information instead of glossed over double-talk.
 

D.Scott

Inactive Registered Visitor
#9
I sure don't want to argue with the anybody on this issue, especially Juran. IMHO I think the "100% inspection is only 80% effective" statement is a cop out used way too much to justify a poor inspection process.

The original study which prompted the statement was done on highly technical circuit boards and the results in such a case were understandable. You can't apply the same statement to an inspection line determining if refrigerators had been coated with red paint.

Obviously, the degree of effectiveness of any inspection is dependent on what you are inspecting for.

I am not a statistician but the logic that the chance of a second inspector finding a single defect would be lower than the first inspector doesn't seem to make sense. The chance of finding the defect would INCREASE for the entire process (using mechanical inspection to eliminate the "he thought - she thought" sceanario).

A process has 100 defects - Inspection 1 (80%) effective finds all but 20. Inspection 2 (80% effective) finds 16 of them. Inspection 3 (also 80% effective) would find 3.2 of the remaining 4.

Can the argument be made that depending on the sensetivity of the inspection, a lot inspected 3 times will catch almost all the defects (ruling out the human side issues mentioned by Kevin and Deming)?

The validity of inspection is dependent on both the criteria for inspection and the process (people/machine). The more complex the inspection criteria, the more intense the process has to be.

If you are inspecting the color of refrigerators, don't be afraid to use the inspectors in Kevin's example. If you are inspecting something else you had better be sure the people you use are dependable, conscientious employees. Short of that, get a good vision system.

When all else fails, remember - IF 100% INSPECTION IS ONLY 80% EFFECTIVE, SORT IT 3 TIMES !!!!!!! :biglaugh:

Dave
 
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