Content by Donald J. Wheeler
What Is the Precision to Tolerance Ratio?And does it define a good measurement system?
Thu, 07/05/2012 - 11:13
In a class last month I was asked to explain a number that occurs in some measurement system evaluations and which is known as the precision to tolerance ratio (P/T ratio). As I will show in this column, it turns out to be related to the capability… Analysis Using Few Data, Part 1Some of these batches are not like the others…
Mon, 06/04/2012 - 13:06
Editor--Part 2 of this article can be found here.
In some industries a few test batches will be produced prior to going into production. When this happens, a critical question is: “Are all of the test batches alike?” With only one value per batch,… When Do We Use Subgrouped Data?A problem with service-sector average charts
Mon, 04/30/2012 - 11:32
When the data come along one value at a time, we tend to put them on a chart for individual values (an XmR chart). Since virtually all business and managerial data occur one value at a time, the primary chart for service-sector data is the XmR chart… When Should We Compute New Limits?How to use the limits to track the process
Mon, 04/02/2012 - 14:51
Last month in “Exact Answers to the Wrong Questions” we looked at how we can compute useful limits with as few as six to 10 values. In this column I would like to consider the question of how to use the limits on a process behavior chart to… Exact Answers to the Wrong QuestionsWhy statisticians still do not understand Shewhart
Fri, 03/02/2012 - 13:52
In a recent article that shall remain nameless, a statistician carefully worked out the exact answer to the wrong question. Then, based on this exact answer, he made an erroneous recommendation regarding the use of a process behavior chart for… If It Ain’t Broke…Problems with narrowly defined projects
Mon, 01/30/2012 - 11:17
The objective of all improvement projects should be to improve the effectiveness, or the efficiency, of the core processes. Everything else should be secondary to this objective. If you improve the efficiency of a support process, or even a portion… Lies, Damned Lies, and Teens Who Smoke While Driving A lack of context is essential to propaganda
Mon, 01/02/2012 - 15:56
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n my February 1996 Quality Digest column I discussed an article out of USA Today. Since that article provides a great example of how we need to filter out the noise whenever we attempt to interpret data, I have updated it for my column today. “… What Is Chunky Data? What happens when the measurement increment gets too large?
Tue, 12/06/2011 - 14:58
Many times measurements are made using measurement increments which are too large for the job. Fortunately this problem is easily detected by ordinary, production-line process behavior charts. No special studies are necessary; no standard parts… Working with Rare Events What happens when the average count gets very small?
Fri, 10/28/2011 - 09:23
From the perspective of data analysis, rare events are problematic. Until we have an event,
there is nothing to count, and as a result many of our time periods will end up with zero counts.
Since zero counts contain no real information, we… What About p-Charts?When should we use the specialty charts for count data?
Fri, 09/30/2011 - 13:26
All charts for count-based data are charts for individual values. Regardless of whether we are working with a count or a rate, we obtain one value per time period and want to plot a point every time we get a value. This is why four specialty…
