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… Analysis Using Few Data, Part 2Comparing the <em>W</em>-ratio test with a homogeneity chart
Wed, 10/24/2012 - 11:40
While an XmR chart is commonly used as a process behavior chart, it may also be used as a test of homogeneity for a finite number of values. This column explains the difference in these two uses of the XmR chart and compares the homogeneity chart… The Heavy-Tailed NormalAnswers to questions
Mon, 10/01/2012 - 13:38
I n my September column, I showed how the normal distribution is the distribution of maximum uncertainty. Now I will expand on that theme and answer the questions generated by that column.
Last month I demonstrated that the middle 91 percent of the… What They Forgot to Tell You About the Normal Distribution How the normal distribution has maximum uncertainty
Tue, 09/04/2012 - 16:03
There are two key aspects of the normal distribution that make it the central probability model in statistics. However, students seldom hear about these important aspects, and as a result they end up making many unnecessary mistakes. Read on to… What Is Leptokurtophobia?And why does it matter?
Mon, 07/30/2012 - 13:17
Three years ago this month Quality Digest Daily published my column, “Do You Have Leptokurtophobia?” Based on the reaction to that column, it contained a message that was needed. In this column I would like to explain the symptoms of… 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…