Tue, 06/01/2021 - 12:03
For more than 40 years it has been common to use the precision to tolerance ratio (P/T ratio) to compare the standard deviation of measurement error with the specified tolerance for a particular product. The purpose of this comparison being an…
Mon, 05/03/2021 - 12:03
In my article, “Tightened 100% Inspection” (Quality Digest, March 29, 2021), we found that the excess costs associated with tightened specification limits are generally prohibitive. Here we consider the question: “Under what conditions can we use…
Mon, 03/29/2021 - 12:03
Inspection sounds simple. Screen out the bad stuff and ship the good stuff. However, measurement error will always create problems of misclassification where good stuff is rejected, and bad stuff gets shipped. While guard-bands and tightened…
Mon, 01/11/2021 - 12:03
In part one we found the baseline portion of an XmR chart to be the best technique for identifying potential outliers among four tests with variable overall alpha levels. In this part we will look at tests which maintain a fixed overall alpha level…
Mon, 12/07/2020 - 12:03
The first statistical test was a test for outliers. The problem of what to do about outliers has been around from the beginnings of data analysis. Part one will compare four tests for outliers. Next month part two will cover some additional tests…
Mon, 11/02/2020 - 11:03
Every introductory class in statistics teaches how to obtain a global standard deviation statistic. While this descriptive statistic characterizes the dispersion of the data, it is not the correct value to use when looking for unusual values within…
Tue, 10/06/2020 - 12:03
On Sept. 29, 2020, the recorded worldwide death toll from Covid-19 reached 1 million. Six days earlier the United States reached 200,000 Covid-related deaths. So how did the United States with only 4 percent of the world’s population manage to…
Wed, 09/09/2020 - 12:03
This article tracks the progression of Covid-19 over the past six months on a state-by-state basis and provides a framework for interpreting these curves by including curves for seven other countries. While 52 states and territories are covered here…
Mon, 08/24/2020 - 12:03
In past articles I have used graphs to provide perspective on how the Covid-19 pandemic is progressing around the world. In this article I shall update some of those graphs and use these historical data to make projections on what may be expected in…
Mon, 08/03/2020 - 12:03
Since the start of the Covid pandemic I have received many questions about how to analyze the Covid numbers using process behavior charts. Various schemes have been proposed and used. This column will discuss appropriate ways of analyzing data from…