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Tips and Techniques for Statistics and Quality Improvement

Blog posts and articles about using Minitab software in quality improvement projects, research, and more.

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

7 Deadly Statistical Sins Even the Experts Make

Do you know how to avoid them?

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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
Allow me to make a confession up front: I won't hesitate to beat my kids at a game. My kids are young enough that in pretty much any game that is predominantly determined by skill and not luck, I can beat them—and beat them easily. This isn't some macho thing where it makes me feel good, and I suppose is only partially based in wanting them to handle both winning and losing well. It's just how I... 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
In my last post, I discussed how a DOE was chosen to optimize a chemical-mechanical polishing process in the microelectronics industry. This important process improved the plant's final manufacturing yields. We selected an experimental design that let us study the effects of six process parameters in 16 runs. Analyzing the Design Now we'll examine the analysis of the DOE results after the actual... Continue Reading
I used to work in the manufacturing industry. Some processes were so complex that even a very experienced and competent engineer would not necessarily know how to identify the best settings for the manufacturing equipment. You could make a guess using a general idea of what should be done regarding the optimal settings, but that was not sufficient. You need very precise indications of the correct... 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
When you analyze a Gage R&R study in statistical software, your results can be overwhelming. There are a lot of statistics listed in Minitab's Session Window—what do they all mean, and are they telling you the same thing? If you don't know where to start, it can be hard to figure out what the analysis is telling you, especially if your measurement system is giving you some numbers you'd think are... Continue Reading
Did you know that March is Women’s History Month? The celebration was started in the 1980s by the U.S. government to pay tribute to generations of influential women. To celebrate, here’s a roundup of just some of the most influential women in statistics: Florence Nightingale While Florence Nightingale is known as the founder of modern nursing, you might not know that she is also a... Continue Reading
Probability. It's really the heart and soul of most statistical analyses. Anytime you get a p-value, you're dealing with a probability. The probability is telling you how likely it was (or will be) for an event to occur. It has numerous applications across a wide variety of areas. But today I want to focus on the probability of a specific event. A basketball tournament. I’ll be using the Sagarin... 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
There has been plenty of noisy disagreement about the state of health care in the past several years, but when you get beyond the controversies surrounding various programs and changes, a great deal of common ground exists. Everyone agrees that there's a lot of waste and inefficiency in the way we've been doing things, and that health care should be delivered as efficiently and effectively as... Continue Reading
I am a bit of an Oscar fanatic. Every year after the ceremony, I religiously go online to find out who won the awards and listen to their acceptance speeches. This year, I was so chuffed to learn that Leonardo Di Caprio won his first Oscar for his performance in The Revenant in the 88thAcademy Awards—after five nominations in  previous ceremonies. As a longtime Di Caprio fan, I still remember... Continue Reading
Like so many of us, I try to stay healthy by watching my weight. I thought it might be interesting to apply some statistical thinking to the idea of maintaining a healthy weight, and the central limit theorem could provide some particularly useful insights. I’ll start by making some simple (maybe even simplistic) assumptions about calorie intake and expenditure, and see where those lead. And then... Continue Reading
After my husband’s most recent visit to the dentist, he returned home cavity-free...and with a $150 electric toothbrush in hand.  I wanted details. It began innocently. His dreaded trip to the dentist ended in high praise for no cavities and only a warning to floss more. That prompted my programming-and-automation-obsessed husband, still in the chair, to exclaim, "I wish there was a way to automate... Continue Reading
The easiest way to determine the probability of being born on a certain day is to assume that every day of the year has an equal probability of being a birthday. But academic scholarship tends to point to seasonal variation in births. If you average statistics from the United Nations, the seasonality in the United States of America from 1969 to 2013, excluding 1976 and 1977, looks like this: Seeing... Continue Reading