Donald J. Wheeler
Students are told that they need to check their data for normality before doing virtually any data analysis. And today’s software encourages this by automatically providing normal probability plots...
Donald J. Wheeler
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. Although the textbooks are full of...
Donald J. Wheeler
Last month we looked at analyzing observational data. Here we will consider experimental data and discover a weakness in the way they are obtained that can contribute to the problem of...
Donald J. Wheeler
Most of the world’s data are obtained as byproducts of operations. These observational data track what happens over time and have a structure that requires a different approach to analysis than that...
Donald J. Wheeler
On the face of it, it seems to be impossible for skewed variables to add up to a normally distributed result. Yet both common experience and mathematical theory combine to show us that this does...
Donald J. Wheeler
Management requires prediction. However, when making predictions it is easy to torture the data until they surrender and tell you what you expect to hear. Even though this torture may be...
Donald J. Wheeler
One of the most common questions about any production process is, “What is the fraction nonconforming?” Many different approaches have been used to answer this question. This article will compare the...
Donald J. Wheeler
First, let it be known that 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...
Donald J. Wheeler
What do the shape statistics known as skewness and kurtosis tell us about our data? Last month we saw how the average and standard deviation define the balance point and radius of gyration for our...
Donald J. Wheeler
Your software routinely gives you four descriptive statistics for your data: the average, the standard deviation, the skewness, and the kurtosis. Of these only the average is easy to understand. This...
