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Data Analysis

Blog posts and articles with tips for analyzing data for quality improvement methodologies, including Six Sigma and Lean.

While many Six Sigma practitioners and other quality improvement professionals like to use the Fishbone diagram in Quality Companion for brainstorming because of its ease of use and integration with other Quality Companion 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... Continue Reading
Analysis of variance (ANOVA) can determine whether the means of three or more groups are different. ANOVA uses F-tests to statistically test the equality of means. In this post, I’ll show you how ANOVA and F-tests work using a one-way ANOVA example. But wait a minute...have you ever stopped to wonder why you’d use an analysis of variance to determine whether means are different? I'll also show how... Continue Reading

7 Deadly Statistical Sins Even the Experts Make

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Among the most underutilized statistical tools in Minitab, and I think in general, are multivariate tools. Minitab offers a number of different multivariate tools, including principal component analysis, factor analysis, clustering, and more. In this post, my goal is to give you a better understanding of the multivariate tool called discriminant analysis, and how it can be used. Discriminant... Continue Reading
You can use contour plots, 3D scatterplots, and 3D surface plots in Minitab to view three variables in a single plot. These graphs are ideal if you want to see how temperature and humidity affect the drying time of paint, or how horsepower and tire pressure affect a vehicle's fuel efficiency, for example. Ultimately, these three graphs are good choices for helping you to visualize your data and exa... Continue Reading
In statistics, t-tests are a type of hypothesis test that allows you to compare means. They are called t-tests because each t-test boils your sample data down to one number, the t-value. If you understand how t-tests calculate t-values, you’re well on your way to understanding how these tests work. In this series of posts, I'm focusing on concepts rather than equations to show how t-tests work.... Continue Reading
Along with the explosion of interest in visualizing data over the past few years has been an excessive focus on how attractive the graph is at the expense of how useful it is. Don't get me wrong...I believe that a colorful, modern graph comes across better than a black-and-white, pixelated one. Unfortunately, however, all the talk seems to be about the attractiveness and not the value of the... Continue Reading
As a recent graduate from Arizona State University with a degree in Business Statistics, I had the opportunity to work with students from different areas of study and help analyze data from various projects for them. One particular group asked for help analyzing online survey data they had gathered from other students, and they wanted to see if their new student program was beneficial. I would... Continue Reading
Did you know about the Minitab Network group on LinkedIn? It’s the one managed by Eston Martz, who also edits the Minitab blog. I like to see what the members are talking about, which recently got me into some discussions about Raman spectroscopy data. Not having much experience with Raman spectroscopy data, I thought I’d learn more about it and found the RRUFFTM Project. The idea is that if you... Continue Reading
Getting your data from Excel into Minitab Statistical Software for analysis is easy, especially if you keep the following tips in mind. Copy and Paste To paste into Minitab, you can either right-click in the worksheet and choose Paste Cells or you can use Control-V. Minitab allows for 1 row of column headers, so if you have a single row of column info (or no column header info), then you can quickly... Continue Reading
T-tests are handy hypothesis tests in statistics when you want to compare means. You can compare a sample mean to a hypothesized or target value using a one-sample t-test. You can compare the means of two groups with a two-sample t-test. If you have two groups with paired observations (e.g., before and after measurements), use the paired t-test. How do t-tests work? How do t-values fit in? In this... Continue Reading
Did you know that Minitab provides several tools you can use to view patterns in data over time? If you want to examine, say, monthly sales for your company, or even how the number of patients admitted to your hospital changes throughout the year, then these tools are for you! 1. Time Series Plot Time series plots are often used to examine daily, weekly, seasonal or annual variations, or... Continue Reading
About a year ago, a reader asked if I could try to explain degrees of freedom in statistics. Since then,  I’ve been circling around that request very cautiously, like it’s some kind of wild beast that I’m not sure I can safely wrestle to the ground. Degrees of freedom aren’t easy to explain. They come up in many different contexts in statistics—some advanced and complicated. In mathematics, they're... Continue Reading
Five-point Likert scales are commonly associated with surveys and are used in a wide variety of settings. You’ve run into the Likert scale if you’ve ever been asked whether you strongly agree, agree, neither agree or disagree, disagree, or strongly disagree about something. The worksheet to the right shows what five-point Likert data look like when you have two groups. Because Likert item data are... 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
Most of us have heard a backwards way of completing a task, or doing something in the conventionally wrong order, described as “putting the cart before the horse.” That’s because a horse pulling a cart is much more efficient than a horse pushing a cart. This saying may be especially true in the world of statistics. Focusing on a statistical tool or analysis before checking out the condition of your... Continue Reading
If you watched television between 1989 and 1993, then you might have had the chance to see original episodes of the television series Quantum Leap. The premise was that a scientist involved in a time-travel experiment gets sent into the bodies of people from the past and has the opportunity to improve the future with his actions. Most of us might not ever get to do something as dramatic as steal a... Continue Reading
Leading and trailing spaces in a data set are like termites in your house. If you don’t realize they are there and you don’t get rid of them, they’re going to wreak havoc. Here are a few easy ways to remove these pesky characters with Minitab Statistical Software prior to analysis. Data Import If you’re importing data from Excel, a text file, or some other file type: Choose File > Open and select your... Continue Reading
P values have been around for nearly a century and they’ve been the subject of criticism since their origins. In recent years, the debate over P values has risen to a fever pitch. In particular, there are serious fears that P values are misused to such an extent that it has actually damaged science. In March 2016, spurred on by the growing concerns, the American Statistical Association (ASA) did... Continue Reading
I live with a German national, who often tells me that we Americans spend way too much of our lives at work. He also frequently comments that we work much less efficiently than Germans do, during the increased time we’re at work.  Which reminds me—I need to pay my water bill online... Okay, I’m back. Quick, wasn’t it? So convenient. Now, where was I? Oh, work habits. After checking the hourly weather... Continue Reading
You have a column of categorical data. Maybe it’s a column of reasons for production downtime, or customer survey responses, or all of the reasons airlines give for those riling flight delays. Whatever type of qualitative data you may have, suppose you want to find the most common categories. Here are three different ways to do that: 1. Pareto Charts Pareto Charts easily help you separate the vital... Continue Reading