Statistics
When a time series displays a pattern that repeats itself periodically it is said to have seasonal effects. The word seasonal may apply to days, weeks, months, quarters, or any pattern that recurs regularly throughout the data. While these seasonal effects will complicate our analysis, their…
In order to do business, we have to use predictions of various sorts. These range from seat-of-the-pants guesses to the results of sophisticated modeling. In every case, the key to effective forecasting is to understand the uncertainty in the forecast. Ways to do this are the subject of this…
With the publication of the new VDA AIAG SPC Manual in July 2026, one of the most significant changes to statistical process control (SPC) in decades has been introduced. While much attention has been given to the new process capability indices, an equally important change is the introduction of…
Some of my colleagues have recently been pushing multivariate charts. These charts combine several different process outcome values into a single number that’s placed on a chart. Unfortunately, this theoretically elegant approach breaks down in practice for reasons that will be explained here.…
Walter Shewhart’s average and range chart had been around for more than a decade when, in 1941, W. J. Jennett came up with the chart for individual values and moving ranges (an XmR chart). The XmR is built on the same foundation as the average and range chart, but it involves two unique ideas.…
The Weibull distribution is a continuous probability distribution often used in reliability analysis to model time-to-failure and product lifespans.
It has applications in engineering, medicine, energy, and insurance. It’s also good at describing survival statistics, such as…