Statman

Hi Malcolm,
 
I do not tell someone something that I don’t believe or that I can’t justify.  
 
I tell them that a six sigma process does not have 3.4 PPM defective it has .001 PPM.  But I also tell them that a six sigma process will be held in statistical control for the long term.  We all know, however, that a process held in statist…[Read more]

Please find a different screen name.  Statman is already taken. 
You ask a good question however, and I think that Stan has given you very sound advice.  Adding a constant to make all values positive before you transform is usually the safest method.
Cheers,
Statman (the original)

Thanks Gabriel, this is a big help

It is a real problem, with real data

Malcolm,
 
You can try to run from this but you can not hide.
 
You say that you have provided an explanation from a credible source.  However, any one that has read Bothe’s book would know that he has no intention to “explain” the shift.  If you notice, this quote that you posted is in the last chapter (14th) of a book on process capabi…[Read more]

SSBB,
You are using a normal approxamation to calculate the confidence intervals for a binomial distribution.  The published article has used the exact calculations from a binomial. 
When  np and n(1-p) are both greater than or equal to five and n is greater than 30, then the normal approximation is pretty good.  If not, as in your case (n(…[Read more]

Hi SSBB,
That should have been: BINOMDIST(1,20,0.25,TRUE) = 0.0243. 
We are looking at the probability of 1 success out of 20 when the true proportion is 25%.  where a success is a mismatch.  The Confidence intervals were determined in Minitab using the 1-proportions test and exact calculations.
Sorry for the error.  I had the right cal…[Read more]

I gave you an answer.  If you don’t like it follow the other advise that you got.  It appears that you do not know enough about what you are doing to follow a lecture.
What is your P-chart telling you?  How are you using a P-chart if you have varing sample size? Shouldn’t you use an np-chart for varing sample size?
Statman

Gabriel,
 
Yes, the control limits are conservative and biased towards preventing a type I error.  This of course makes sense we have a situation where the cost of adjustment to a process is high relative to the cost of small shifts in the process.  We tend to treat these alpha risks as if they were handed down by God and surely, I think we co…[Read more]

Gabriel,
 
As usual, you make some very good points. 
 
To build on what you are saying, I would rather see the BB close the project when they have reached the point of dimensioning return on the project rather than continue to try to work toward an unrealistic goal.  Too often, we start the project by swagging an unrealistic goal.  It is n…[Read more]

Lets see, sequential months of data and I want to know if there has been a shift in the process……I don’t know maybe I could use a
CONTROL CHART
Try either a C-chart or a U-chart.
And fire the trainer that led you to believe that this is an application of hypithesis testing.
Statman

Joe,
 
Thank you for the compliment on my post.
 
I have yet to see a good reference for attribute Gage R&R that includes a discussion of Cohen’s kappa coefficient.  Although I have not spent anytime looking for one so there may be one out there.  A brief but very good discussion of Kappa is in the following Quality Progress art…[Read more]

Newby,
 
Your Quality Guru is full of it.
 
As is often the case, the Guru is misinterpreting the concept of confidence intervals.  All values within a confidence interval do not have equal likelihood of occurrence.   There is not a uniform distribution of probability across the CI.  A better way to state the question is:  given the true p…[Read more]

PA,
 
You have received some interesting advice on your question.  I am not sure if you feel better or worse about your situation so let me see if I can help.  Actually, Tim Folkerts’ strategy was on the right track so I am just going to build off of what he was doing. 
 
What you want to do is test the minimum number of parts that will tell…[Read more]

Who’s mathematics?  Do you really believe that parameters estimated from a process in statistical control will be off by that much?
You have been drinkin too much from the well of Dr Harry
So what is Ppk in worse case? 
Statman

Interesting set of articles.
 
You not have noticed the little caveat in their discussion of the dangers of Cpk.  If not I pasted it below:
 
“(Yes, for this example, we have ignored the first cardinal rule: Before one looks at Cpk, the process must be in control.)”
 
This of course invalids any thing the author is saying about Cpk.  Makes…[Read more]

You said:
“cpk is not a good measure because it is always inflated(more sub group size more better cpk)…….  with cpk 1.33 you can have 0.65% out of spec parts”
What in the ____ are you talking about?
Statman

You have done successful Six Sigma Projects both at Stategic and Operations level and 36 years of business and academic experience plus a phd and yet you were still compelled to take this exam.
Why?  Do you have some sort of neurotic need for approval?
What if you would have failed?  Would you have considered your whole life to be a l…[Read more]

Now your talkin’ my language!
Throw in a few Belgium beers and we can have an interesting debate
Cheers,
Statman

You know Darth,
 
I wish I was as optimistic as you about the discriminating powers of the market.  I can’t help but think about the scene in the movie “Raiders of Silicone Valley”  where Bill Gates tells Steve Jobs that it is not about who has the best equipment or who has the best software, it is about who can sell it (or something like that)…[Read more]