Issues with Data Collection – the Flint MI Water Crisis

The city of Flint, Michigan changed its water source from the Detroit water system to the Flint River in April, 2014 in order to save money.  Residents soon began to complain about the water’s color, taste and odor, and to report rashes and concerns about bacteria.  The Flint city government proclaimed at that time that […] read more

On July 30th, 2016, posted in: Six Sigma by Tags: ,

Overdispersion of data

One of my Master Black Belt students sent me an inquiry about a manufacturing process that was producing a very small percentage of scrap.  He was having trouble understanding the control charts that he had created from his data and was convinced that he needed to perform a transformation on the underlying data. I started […] read more

On July 20th, 2016, posted in: Project Management by

Lies and Statistics……

One of my Black Belt students recently submitted his final project report.  He used the two proportions test in Minitab to compare the proportion of on time performance for completion of employee appraisals, before and after improvement.  I sent him the following feedback regarding this test. “Hi.  Your null and alternate hypotheses are correctly stated.  […] read more

On July 9th, 2016, posted in: Articles, Six Sigma by Tags: ,

The Central Limit Theorem

Although the central limit theorem can seem abstract and devoid of any practical application, this theorem is actually quite important to the practice of statistics.  As we will see, this theorem allows us to make some assumptions about a population. In order to understand the basis for the Central Limit Theorem, consider a population of […] read more

On June 16th, 2016, posted in: Articles, Six Sigma by Tags: ,