More to Beware About Tukey Control ChartsAnswers to questions asked
Mon, 09/09/2013 - 15:50
Last month’s column, “Beware the Tukey Control Chart,” generated several questions of a fundamental nature that deserve expanded answers. These questions and their answers will be considered here.
Interquartile ranges
The Tukey control chart uses… Beware the Tukey Control ChartAnother bad idea surfaces
Mon, 08/05/2013 - 16:06
I recently read about a technique for analyzing data called the "Tukey control chart." Since Professor John Tukey is no longer with us, it appears that someone without his brilliance has tried to adapt one of his techniques into an alternative type… The Problem of Long-Term CapabilityPoor labels lead to incorrect ideas
Mon, 07/08/2013 - 14:38
Based on some recent inquiries there seems to be some need to review the four capability indexes in common use today. A clear understanding of what each index does, and does not do, is essential to clear thinking and good usage. To see how to use… Why We Keep Having 100-Year FloodsMaking predictions using historical data
Tue, 06/04/2013 - 00:00
All data are historical. All analyses of data are historical. Yet all of the interesting questions about our data have to do with using the past to predict the future. In this article I shall look at the way this is commonly done and examine the… Contra Two SigmaThe consequences of using the wrong limits
Wed, 05/01/2013 - 10:27
You may occasionally encounter charts with two-sigma limits. The origins of this practice are not clear, and no real justification of this practice has been given in the literature. In this article, I will consider the theoretical and practical… Consistency ChartsSPC for measurement systems
Wed, 03/27/2013 - 11:15
What happens when we measure the same thing and get different values? How can we ever use such a measurement system to measure different things? By thinking of measurements as the product and the measurement procedure as the process we can use the… Right and Wrong Ways to Use SpecificationsShould you sort it or adjust it?
Wed, 02/27/2013 - 11:01
Last month I looked at "The Secret of Process Adjustment." This column will review the history and purpose of specifications and look at two common ways that specifications are used in practice. Using simple examples I will illustrate the right… The Secret of Process AdjustmentUnneeded adjustments always make things worse
Tue, 01/29/2013 - 13:30
When your process outcomes are not what you expect them to be it is common to adjust the process. This is not always appropriate. To understand when adjustments are appropriate, and when they are inappropriate, we will need to learn how to… But the Limits Are Too Wide!When the <em>XmR</em> Chart Doesn’t Seem to Work
Wed, 01/02/2013 - 13:13
Last month I described what makes the XmR chart work. This month I will describe some common failure modes for the XmR chart and show how they come from a failure to follow the two fundamental principles behind the XmR chart.
When administrative… What Makes the XmR Chart Work?How does it separate the signals from the noise?
Thu, 11/29/2012 - 13:39
There are two basic ideas or principles that need to be respected when creating a chart for individual values and a moving range (an XmR chart). This column will explain and illustrate these two principles for effective XmR charts.
The first…
