Tips and Techniques for Statistics and Quality Improvement

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

True or false: When comparing a parameter for two sets of measurements, you should always use a hypothesis test to determine whether the difference is statistically significant. The answer? (drumroll...) True! ...and False! To understand this paradoxical answer, you need to keep in mind the difference between samples, populations, and descriptive and inferential statistics.  Descriptive Statistics and... Continue Reading
Data mining uses algorithms to explore correlations in data sets. An automated procedure sorts through large numbers of variables and includes them in the model based on statistical significance alone. No thought is given to whether the variables and the signs and magnitudes of their coefficients make theoretical sense. We tend to think of data mining in the context of big data, with its huge... Continue Reading

7 Deadly Statistical Sins Even the Experts Make

Do you know how to avoid them?

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Today, September 16, is World Ozone Day. You don't hear much about the ozone layer any more. In fact, if you’re under 30, you might think this is just another trivial, obscure observance, along the lines of International Dot Day (yesterday) or National Apple Dumpling Day (tomorrow). But there’s a good reason that, almost 30 years ago, the United Nations designated today to as a day to raise... Continue Reading
I confess: I'm not a natural-born decision-maker. Some people—my wife, for example—can assess even very complex situations, consider the options, and confidently choose a way forward. Me? I get anxious about deciding what to eat for lunch. So you can imagine what it used to be like when I needed to confront a really big decision or problem. My approach, to paraphrase the Byrds, was "Re:... Continue Reading
The other day I was talking with a friend about control charts, and I wanted to share an example one of my colleagues wrote on the Minitab Blog.  Looking back through the index for "control charts" reminded me just how much material we've published on this topic. Whether you're just getting started with control charts, or you're an old hand at statistical process control, you'll find some valuable... Continue Reading
To assess if a process is stable and in statistical control, you can use a control chart. It lets you answer the question "is the process that you see today going to be similar to the process that you see tomorrow?" To assess and quantify how well your process falls within specification limits, you can use capability analysis. Both of these tools are easy to use in Minitab, but you first need to... Continue Reading
You’ve performed multiple linear regression and have settled on a model which contains several predictor variables that are statistically significant. At this point, it’s common to ask, “Which variable is most important?” This question is more complicated than it first appears. For one thing, how you define “most important” often depends on your subject area and goals. For another, how you collect... Continue Reading
There may be huge potential benefits waiting in the data in your servers. These data may be used for many different purposes. Better data allows better decisions, of course. Banks, insurance firms, and telecom companies already own a large amount of data about their customers. These resources are useful for building a more personal relationship with each customer. Some organizations already use... Continue Reading
The college football season is here, and this raises a very important question: Is Alabama going to be undefeated when they win the national championship, or will they lose a regular-season game along the way? Okay, so it's not a given that Alabama is going to win the championship this year, but when you've won 4 of the last 7 you're definitely the odds-on favorite. However, what if we wanted to take... Continue Reading
If you’re in the market for statistical software, there are many considerations and more than a few options for you to evaluate. Check out these seven questions to ask yourself before choosing statistical software—your answers should help guide you towards the best solution for your needs! 1. Who uses statistical software in your organization? Are they expert statisticians, novices, or a mix of both?... Continue Reading
In 2011 we had solar panels fitted on our property. In the last few months we have noticed a few problems with the inverter (the equipment that converts the electricity generated by the panels from DC to AC, and manages the transfer of unused electric to the power company). It was shutting down at various times throughout the day, typically when it was very sunny, resulting in no electricity being... 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
So the data you nurtured, that you worked so hard to format and make useful, failed the normality test. Time to face the truth: despite your best efforts, that data set is never going to measure up to the assumption you may have been trained to fervently look for. Your data's lack of normality seems to make it poorly suited for analysis. Now what? Take it easy. Don't get uptight. Just let your data... Continue Reading
See if this sounds fair to you. I flip a coin. Heads: You win $1.Tails: You pay me $1. You may not like games of chance, but you have to admit it seems like a fair game. At least, assuming the coin is a normal, balanced coin, and assuming I’m not a sleight-of-hand magician who can control the coin. How about this next game? You pay me $2 to play.I flip a coin over and over until it comes up heads.Your... Continue Reading
I thought 3 posts would capture all the thoughts I had about B10 Life. That is, until this question appeared on the Minitab LinkedIn group: In case you missed it, my first post, How to Calculate B10 Life with Statistical Software, explains what B10 life is and how Minitab calculates this value. My second post, How to Calculate BX Life, Part 2, shows how to compute any BX life in Minitab. But... Continue Reading
The Centers for Medicare and Medicaid Services (CMS) updated their star ratings on July 27. Turns out, the list of hospitals provide a great way to look at how easy it is to get random samples from data within Minitab. Say for example, that you wanted to look at the association between the government’s new star ratings and the safety rating scores provided by hospitalsafetyscore.org. The CMS score... Continue Reading
Back when I used to work in Minitab Tech Support, customers often asked me, “What’s the difference between Cpk and Ppk?” It’s a good question, especially since many practitioners default to using Cpk while overlooking Ppk altogether. It’s like the '80s pop duo Wham!, where Cpk is George Michael and Ppk is that other guy. Poofy hairdos styled with mousse, shoulder pads, and leg warmers aside, let’s... Continue Reading
Figures lie, so they say, and liars figure. A recent post at Ben Orlin's always-amusing mathwithbaddrawings.com blog nicely encapsulates why so many people feel wary about anything related to statistics and data analysis. Do take a moment to check it out, it's a fast read. In all of the scenarios Orlin offers in his post, the statistical statements are completely accurate, but the person offering... Continue Reading
Often, when we start analyzing new data, one of the very first things we look at is whether certain pairs of variables are correlated. Correlation can tell if two variables have a linear relationship, and the strength of that relationship. This makes sense as a starting point, since we're usually looking for relationships and correlation is an easy way to get a quick handle on the data set we're... Continue Reading
The Olympic games are about to begin in Rio de Janeiro. Over the next 16 days, more than 11,000 athletes from 206 countries will be competing in 306 different events. That's the most events ever in any Olympic games. It's almost twice as many events as there were 50 years ago, and exactly three times as many as there were 100 years ago. Since the number of Olympic events has changed over time,... Continue Reading