Marilyn Wheatley

Marilyn Wheatley is a technical support specialist at Minitab Inc. 

Users often contact Minitab technical support to ask how the software calculates the control limits on control charts. A frequently asked question is how the control limits are calculated on an I-MR Chart or Individuals Chart. If Minitab plots the upper and lower control limits (UCL and LCL) three standard deviations above and below the mean, why are the limits plotted at values other than 3 times... Continue Reading
As a person who loves baking (and eating) cakes, I find it bothersome to go through all the effort of baking a cake when the end result is too dry for my taste. For that reason, I decided to use a designed experiment in Minitab to help me reduce the moisture loss in baked chocolate cakes, and find the optimal settings of my input factors to produce a moist baked chocolate cake. I’ll share the... Continue Reading



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While there are many graph options available in Minitab’s Graph menu, there is no direct option to generate a waterfall chart. This type of graph helps visualize the cumulative effect of sequentially introducing positive or negative values. In this post, I’ll show you the steps to follow to make Minitab display a waterfall chart even without a "waterfall chart" tool. If you don’t already have... Continue Reading
Since the release of Minitab Express in 2014, we’ve often received questions in technical support about the differences between Express and Minitab 17.  In this post, I’ll attempt to provide a comparison between these two Minitab products. What Is Minitab 17? Minitab 17 is an all-in-one graphical and statistical analysis package that includes basic analysis tools such as hypothesis testing,... Continue Reading
In regression, "sums of squares" are used to represent variation. In this post, we’ll use some sample data to walk through these calculations. The sample data used in this post is available within Minitab by choosing Help > Sample Data, or File > Open Worksheet > Look in Minitab Sample Data folder (depending on your version of Minitab).  The dataset is called ResearcherSalary.MTW, and contains data... Continue Reading
While some posts in our Minitab blog focus on understanding t-tests and t-distributions this post will focus more simply on how to hand-calculate the t-value for a one-sample t-test (and how to replicate the p-value that Minitab gives us).  The formulas used in this post are available within Minitab Statistical Software by choosing the following menu path: Help > Methods and Formulas > Basic... Continue Reading
Here is a scenario involving process capability that we’ve seen from time to time in Minitab's technical support department. I’m sharing the details in this post so that you’ll know where to look if you encounter a similar situation. You need to run a capability analysis. You generate the output using Minitab Statistical Software. When you look at the results, the Cpk is huge and the histogram in... Continue Reading
While many Six Sigma practitioners and other quality improvement professionals like to use the Fishbone diagram in Companion for brainstorming because of its ease of use and integration with other Companion by Minitab tools, some Minitab users find an infrequent need for a Fishbone diagram. For the more casual user of the Fishbone diagram, Minitab has the right tool to get the job done. Minitab’s... Continue Reading
We often receive questions about moving ranges because they're used in various tools in our statistical software, including control charts and capability analysis when data is not collected in subgroups. In this post, I'll explain what a moving range is, and how a moving range and average moving range are calculated. A moving range measures how variation changes over time when data are collected as... Continue Reading
Since opening a new office in Phoenix to support our customers on the West Coast, some evenings in Minitab technical support feel busier than others. (By evenings, I mean after 5:30 p.m. Eastern time, when the members of our tech support team in Pennsylvania go home for the day, and I become an office of one.) The variability in terms of days that felt extremely busy versus days that didn’t... Continue Reading
In this post, I’ll address some common questions we’ve received in technical support about the difference between fitted and data means, where to find each option within Minitab, and how Minitab calculates each. First, let’s look at some definitions. It’s useful to have an example, so I’ll be using the Light Output data set from Minitab’s Data Set Library, which includes a description of the sample... Continue Reading
In my last post, I walked through the steps to install Minitab 17 on a Mac using Apple Boot Camp.  Minitab 17 can also be installed on a Mac using desktop virtualization software. In addition to your Mac, you’ll need: A copy of Windows 7 or later version ISO Minitab 17 Statistical Software Desktop virtualization software allows you to install and use Windows on your Intel-based Mac without requiring... Continue Reading
While Minitab 17 is currently a Windows-only application, there are people who only have a Mac available for the installation who also find they need to use Minitab 17.  It is possible to run Minitab 17 on a Macintosh, though the steps involved in the installation can seem a little daunting at first. In the Technical Support department, we sometimes hear reluctance in people’s voices when we throw... Continue Reading
While most of us work in Minitab Statistical Software using our preferred language, some need to share Minitab project files or present the results in a different language. Others among us just want to play around with the languages because playing around with Minitab is fun! Thankfully, Minitab offers our statistical softwarein eight languages, including English, French, German, Japanese, Korean,... Continue Reading
When data are collected in subgroups, it’s easy to understand how the variation can be calculated within each of the subgroups based the subgroup range or the subgroup standard deviation. When data is not collected in subgroups (so the subgroup size is 1), it may be a little less intuitive to understand how within-subgroup standard deviation is calculated.  How does Minitab Statistical Softwarecalcu... Continue Reading
The two previous posts in this series focused on manipulating data using Minitab’s calculator and the Data menu. In this third and final post, we continue to explore helpful features for working with text data and will focus on some features in Minitab’s Editor menu. Using the Editor Menu  The Editor menu is unique in that the options displayed depend on what is currently active (worksheet, graph,... Continue Reading
My previous post focused on manipulating text data using Minitab’s calculator. In this post we continue to explore some of the useful tools for working with text data, and here we’ll focus on Minitab’s Data menu. This is the second in a 3-part series, and in the final post we’ll look at the new features in Minitab’s Editor menu. Using the Data Menu When I think of the Data menu, I think... Continue Reading
With Minitab, it’s easy to create graphs and manage numeric, date/time and text data. But Minitab’s enhanced data manipulation features make it easier to work with text data, too. This is the first of three posts in which I'm going to focus on various tools in Minitab that are useful when working with text data, including the Calculator, the Data menu, and the Editor menu. Using the Calculator You... Continue Reading
In technical support, we often receive questions about Gage R&R and how Minitab calculates the amount of variation that is attributable to the various sources in a measurement system. This post will focus on how the variance components are calculated for a crossed Gage R&R using the ANOVA table, and how we can obtain the %Contribution, StdDev, Study Var and %Study Var shown in the Gage R&R output. ... Continue Reading
Minitab's capability analysis output gives you estimates of the capability indices Ppk and Cpk, and we receive many questions about the difference between them. Some of my colleagues have taken other approaches to explain the difference between Ppk and Cpk, so I wanted to show you how they differ by detailing precisely how each one is calculated.  When you're using statistical softwarelike Minitab,... Continue Reading