Content by Donald J. Wheeler
When Can We Trust the Limits On a Process Behavior Chart?Don’t the outliers distort the limits?
Tue, 05/26/2009 - 13:55
Last month we showed the X chart in figure 1. The four lowest values and the three highest values were seen to be “outliers” when we looked at the histogram. When we fitted a bell-shaped curve to the histogram, the outliers corrupted the model and…
All Outliers Are EvidenceRemoving the extreme values is always a serious mistake.
Sun, 05/03/2009 - 15:07
Many have been taught that they must remove outliers prior to analysis. This is because much of modern statistics is concerned with creating a mathematical model for the data. Because all these models are created using algorithms, they tend to be…
No Data Have Meaning Without ContextHow should you organize and plot your data?
Tue, 03/31/2009 - 11:27
As Davis Balestracci frequently emphasized in his column, “RealWorldSPC,” published in Quality Digest for four years, it is fundamental to understand the context of the data before you begin to do any computations. It is the background for your…
Probability Models Don’t Generate Your Data Don’t start your analysis by asking, “How are these data distributed?”
Fri, 02/27/2009 - 10:19
The number of major hurricanes in the Atlantic since 1940 (as we considered in my February column, “First, Look at the Data”) are shown as a histogram in figure 1, below. Some analysts would begin their treatment of these data by considering…
First, Look at the DataWhat can we learn from the historical record?
Thu, 01/29/2009 - 14:03
I recently received a data set consisting of the number of major hurricanes in the North Atlantic from 1940 to 2007. (Major hurricanes are those that reach Category 3 status or higher at some point during their existence.) The first step in…
Multivariate ChartsHow to torture your data into submission
Thu, 08/06/2026 - 13:07
Some of my colleagues have recently been pushing multivariate charts. These charts combine several different process outcome values into a single number that is placed on a chart. Unfortunately, this theoretically elegant approach breaks down in…