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

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Jim Biz

THINK ABOUT??

I seem to come to grips with understanding 80-20 thing from the "outside/flipside" of the box way of thought.

energy - 80-20 has nothing to do with tired - or unqualified - or unmotivated inspectors - or bad inspection techniques.
its just plain more difficult to find bad ones when there are fewer to find. (unless of course we're talking the difference between black & white paint.) Even "top management folks" could find 5 elephants - amongst 25 donkeys. ;)

Discovering say 4 known bad parts out of 100 gives me 25:1 chance of finding them - If I find & remove 3 and do a second 100% inspection then my odds are 97:1 of finding the ones that are left.
 
D

D.Scott

Once again - I am not a statistician - BUT - multiplying the 80%s doesn't seem to be valid here. I agree you would multiply the probabilities to determine the probability of something happening a given number of times in succession. I don't believe this is the question for this situation.

In this instance, we are looking at an 80/100 chance of finding a defect on the first pass PLUS a 16/20 (80%) chance on the second and PLUS a 3.2/4 (80%) chance on the third. The chance of discovery increases with each addition to a 99.2/100 probability that the defect will be found. :confused:

Jim's example would only be valid if samples were scrapped randomly (ie. pick out one - chances are 1 in 25 that it is a bad one).

Of course, I could be wrong. Who is our stats whiz? :ko:

Dave
 
S

Sam

Just for the record, I checked my 4th ed of Jurans handbook and was unable to determine that he made the comment that 100% inspection is only 80% effective. What he did say about 100% inspection is outlined on page 18.25.
Maybe someone is confusing this with his development of the pareto chart.
 
E

energy

All right, Sam

The Pied Piper story is all too familiar to me! Let's keep it going. It made for a lot of interesting and thought provoking posts. Show me the money! :p :smokin:
 
J

JRKH

Just read through this post this morning.

While I was reading it my wife piped up from the other room about the how the government is wanting to federalize the airport checking posts. She says, "CNN keeps reporting these incidences of people getting by".

I responded, "How many stories are you hearing about them finding things."

"None".

"Well then we don't know how effective the current system really is. Do you think that the Federal Government will be more effective?


Now I don't want to get political here, but this issue seems to fit right in with the discussion we are having here.
How effective is the current system?

Just some more fuel for the..... MMMM,,, I mean food for thought.

James
 
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Kevin Mader

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Inspection efficiency is made up of many factors, those contributing to the success of detection, the others contributing to noise. Juran’s estimation of 80% efficiency is based on the noise factor interfering with 100% detection in his personal experiences over the many years in industry. Think of Man, Machine/Equipment, Method, and Material. Now think of the possible noise contributing to the inefficiency of any one of these inputs. If Juran is right, then all the noise will reduce my ability to detect a defect by 20% regardless of the fraction defective in the lot. The lower the fraction defective, the lower my probability of detecting it. This is also an exponential function, not a linear regression.

James presents a good topic for discussion: the efficiency of private screening services at airports. Think about Man, Machine/Equipment, Method, and Material. Will the federal government do a better job in any one of these aggregates? Marc’s comments in correcting me are right on the money. What can be done to the process to poka yoke it (this will reduce the noise factor and increase detection)? What low cost/no cost modifications be done immediately to improve security? What more costly solutions can be instituted provided there is data to support the expenditure?

Suppose there is a 95% efficiency in the category Man, 95% in Machine/equipment, 95% efficiency in Method, and 95% efficiency in Material. What is the System’s overall efficiency (they are all interrelated)? Here is something posted by Don Winton (our Stats Wizard) on September 28, 1998 that explains System's Thinking:

“…Possibly. I prefer to think of this particular case as a lack of systems thinking. Each of the solid boosters had three joints. The specification read that each joint had to have a less than 2% probability of failure during any single firing. The testing verified this to be the case (satisfied the specified requirements). Now, let us look at the system requirement.

Each system contained two solid rocket boosters, each with three seals that had met the 98% probability of success. What is the probability of a system failure?

This is defined as (0.98)^6 = 0.886 or 88.6% So, for each system launch, there is a 88.6% probability of success!!!!!! By the time STS-56 was launched, it only had a 50% chance of success. That is a lack of system thinking personified!…”

Did this just muddy the water?

Kev
 
E

energy

I got it!

Kevin,

A good set of ear muffs with a 33RB Protection factor should take care of the noise factor:bigwave:

In the case of the seals, just like your underwear, you change them to keep the "protection" factor up. Also, saves the waistband:ko: :smokin: You know I'm just being a "prisoner" of my limited capacity to comprehend statistics. Forgive me!:)) :smokin:
 
D

D.Scott

YUP !! :ko:

Thanks for trying though.

Here is my scenario - The bad part gets past the first inspector, OK nobody's perfect. The part gets past the second inspector too, I get a little skeptical. The part gets past a third inspector as well? Somebody is not paying attention - period. We are going to spend a few quality moments together.

Then again, in our business it isn't too far from elephants in a pasture of donkeys. Anything critical, we use vision systems.

Dave :bigwave:
 

SteelMaiden

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Am I a pessimist or does anyone else feel that putting the federal government in charge of security is going to cost us way more than revamping the private security practices? Even if the private companies brought wages into line, hired citizens that passed a background check etc., don't you think it would be cheaper for the American Taxpayer?

I don't think that having a federal employee doing inspections is going to be any more effective than a private employee (provided he is being fairly compensated.) Actually, having spent some time around govt. employees, I'd guess that with the rampant entitlement attitude, the govt. employee might be more prone to slack off knowing that it takes eons to oust someone who doesn't do their job.

Now, I don't want anyone who is a govt. employee to get offended, there are a lot of them out there that are good, concientious people. For them, I say good work and thanks. But I have met a lot through the years that just plain don't give a hoot about their job other than that retirement check they will be eligible for.

Sorry for bringing politics into it...I just think that the government gets too involved in too many things it has no knowledge about.
 
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