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Statistics

Blog posts and articles about statistical principles in quality improvement methods like Lean and Six Sigma.

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

7 Deadly Statistical Sins Even the Experts Make

Do you know how to avoid them?

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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
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
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
I’ve written about R-squared before and I’ve concluded that it’s not as intuitive as it seems at first glance. It can be a misleading statistic because a high R-squared is not always good and a low R-squared is not always bad. I’ve even said that R-squared is overrated and that the standard error of the estimate (S) can be more useful. Even though I haven’t always been enthusiastic about... Continue Reading
Mind the gap. It's is an important concept to bear in mind whilst traveling on the Tube in London, the T in Boston, the Metro in Washington, D.C., etc. But how many of us remember to mind the gap when we create an interval plot in Minitab Statistical Software? Not too many of us, I'd wager. And it's a shame, too. When you travel on the subway, minding the gap means giving thoughtful consideration... Continue Reading
In my last post, I looked at viewership data for the five seasons of HBO’s hit series Game of Thrones. I created a time series plot in Minitab that showed how viewership rose season by season, and how it varied episode by episode within each season.   My next step is to fit a statistical model to the data, which I hope will allow me to predict the viewing numbers for future episodes.    I am going to... Continue Reading