No, Mike; I’m not trying to imply that you don’t know the difference
between spec limits and control limits; had I believed that, I wouldn’t
have asked the question that way. I just wanted to know how you are using
those controllers (I’d still like to know).
I also realize that most people don’t use cigarette lighters any more
(although they…[Read more]
I’m not sure how they arrive at that; of course, operational definitions are important. Here’s how I did it: If you use =NORM.S.DIST(-6,TRUE) in Excel, you get 0.000000000987 for the percent of the curve to the left of 6 sigma; doubling that for the other tail yields 0.000000001973, which translates to about 2ppb. That is what I have seen in…[Read more]
That sounds about right, Mike. I’m very glad to hear that the shift has become a footnote, at least here. I talked to Mikel Harry back in about 2011…at the time, I was on a couple of ANSI TAGs, including one for statistical methods. When I joined, they were putting the final touches on a DMAIC standard, in which they explained the metric and the…[Read more]
I just found an old discussion where people were talking about the possibility of a “negative process sigma.”
This, to me, illustrates a couple of problems:
1. General misunderstanding of process capability
2. The problem with trying to use a metric like process sigma in the first place.
1. In that discussion, one author accused another of not…[Read more]
Rip Stauffer commented on the post, Case Study: Using np Charts To Address On-Time Medication Delivery 3 years, 8 months ago
Not bad…the Pareto Chart is missing some things, though. The left scale is generally counts, while the right scale is percentages of the whole.
Rip Stauffer commented on the post, Of Processes and Project Baselines: Why Homogeneity Matters 6 years ago
The bowl of beads is a universe, because it’s a population. When we use the term “universe” we are using it to mean the whole that we are studying. When you have a population (about which it is, at least in […]
In his original book, Walter Shewhart concluded that normality was neither sufficient nor required for a state of statistical control. In point of fact, most control charts actually do not “require” normality. Normality is nice, but what’s important is that the data be reasonably unimodal and symmetrical. For some of the WE Zone tests, a bell…[Read more]