Content by Donald J. Wheeler
Process Behavior Charts for Non-Normal Data, Part 2What happens to the range chart?
Tue, 02/03/2015 - 15:41
Whenever the original data pile up against a barrier or a boundary value, the histogram tends to be skewed and non-normal in shape. Last month in part one we found that this doesn’t appreciably affect the performance of process behavior charts for… Process Behavior Charts for Non-Normal Data, Part 1A guide for charts for location
Tue, 01/06/2015 - 15:24
Whenever the original data pile up against a barrier or a boundary value, the histogram tends to be skewed and non-normal in shape. In 1967 Irving W. Burr computed the appropriate bias correction factors for non-normal probability models. These… A Tale of Two ComparisonsAre these two processes the same?
Tue, 12/02/2014 - 11:58
Comparisons are often required as part of doing business. Are these two machines the same? Is this process the same as that process? Are two operators performing in the same way? In this article we will look at two ways of making these comparisons… Obey GravityIt’s the law
Mon, 11/03/2014 - 09:48
There is no virtue in obedience when we do not have a choice. But when we have a choice it helps to understand both the law and the reason behind the law. This column is about bad choices that are being made on a daily basis by the users of… Don’t We Need to Remove the Outliers?Characterization and estimation are different
Mon, 10/06/2014 - 10:56
Much of modern statistics is concerned with creating models which contain parameters that need to be estimated. In many cases these estimates can be severely affected by unusual or extreme values in the data. For this reason students are often… A Problem With Outlier TestsWhen can you really use Dixon’s test?
Tue, 09/02/2014 - 18:26
Outlier tests such as the W-ratio test and Dixon’s outlier test suffer from a problem that can mislead the user. This article will outline the problem and provide guidelines for the appropriate use of these tests.
Dixon’s outlier test
In 1953, W.… The Truth About Acceptance Sampling,
Part 2How to avoid asking the wrong question
Mon, 08/04/2014 - 09:11
One of the common tools of quality assurance is acceptance sampling. Acceptance sampling uses the observed properties of a sample drawn from a lot or batch to make a decision about whether to accept or reject that lot or batch. While the textbooks… The Truth About Acceptance Sampling,
Part 1What can you say about this lot?
Wed, 07/02/2014 - 00:00
One of the common tools of quality assurance is acceptance sampling. Acceptance sampling uses the observed properties of a sample drawn from a lot or batch to make a decision about whether to accept or reject that lot or batch. Textbooks are full of… What Is an Alpha-Level?The alpha-level specifies our attitude to the analysis
Tue, 06/10/2014 - 00:00
One thing burned into the brains of those who survive a statistics class is that you have to specify an alpha-level before you do anything statistical. And when it comes to statistical inference, they are correct. But just what does the alpha-level… What Are Good Measurements?Consistency trumps precision
Mon, 05/19/2014 - 18:06
Who could ever be against having good measurements? Good measurements are like apple pie and motherhood. Since we all want good measurements, it sounds reasonable when people are told to check out the quality of their measurement system before…
