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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.

Using statistical techniques to optimize manufacturing processes is quite common now, but using the same approach on social topics is still an innovative approach. For example, if our objective is to improve student academic performances, should we increase teachers wages or would it be better to reduce the number of students in a class? Many social topics (the effect of increasing the minimum... Continue Reading
The no-hitter is one of the most impressive feats in baseball. It’s no easy task to face more than 27 batters without letting one of them get a hit. So naturally, no-hitters don’t occur very often. In fact, since 1900 there has been an average of only about 2 no-hitters per year. But what if you had the opportunity to bet that one wouldn’t occur? That’s exactly what happened to sportswriter C. Trent... Continue Reading
You might not have known, but September is Attendance Awareness Month. Specifically, attendance of children at American public schools. The organization Attendance Works recently came out with a report that highlights the learning gap between students with strong attendance and students with poor attendance. Statistical software helps us quickly and easily create graphs that make it easier to... Continue Reading
The word kurtosis sounds like a painful, festering disease of the gums. But the term actually describes the shape of a data distribution. Frequently, you'll see kurtosis defined as how sharply "peaked" the data are. The three main types of kurtosis are shown below. Lepto means "thin" or "slender" in Greek. In leptokurtosis, the kurtosis value is high. Platy means "broad" or "flat"—as in duck-billed pl... Continue Reading
In my previous post, I described how I was asked to weigh in on the ethics of researchers (DeStefano et al. 2004) who reportedly discarded data and potentially set scientific knowledge back a decade. I assessed the study in question and found that no data was discarded and that the researchers used good statistical practices. In this post, I assess a study by Brian S. Hooker that was... Continue Reading
The other day I received a request from a friend to look into a new study in a peer reviewed journal that found a link between MMR vaccinations and an increased risk of autism in African Americans boys. To draw this conclusion, the new study reanalyzed data that was discarded a decade ago by a previous study. My friend wanted to know, from a statistical perspective, was it unethical for the... Continue Reading
Did you just go shopping for school supplies? If you did, you’ve participated in what’s become the second biggest spending season of the year in the United States, according to the National Retail Federation (NRF). The trends and analysis are so interesting to the NRF that they actually add questions about back-to-school shopping to two monthly consumer surveys. The two surveys have different... Continue Reading
Previously, I showed why there is no R-squared for nonlinear regression. Anyone who uses nonlinear regression will also notice that there are no P values for the predictor variables. What’s going on? Just like there are good reasons not to calculate R-squared for nonlinear regression, there are also good reasons not to calculate P values for the coefficients. Why not—and what to use instead—are the... Continue Reading
A mere 10 seasons ago, USC and Oklahoma opened the college football season ranked #1 and #2 in the preseason AP Poll and the Coaches Poll. They remained there the entire regular season, as neither lost a game. But as chance would have it, they weren’t the only undefeated teams that year. Both Auburn and Utah went undefeated, but neither could crack the top 2, and Oklahoma and USC went on to play... Continue Reading
by The Discrete Sharer, guest blogger As Minitab users, many of us have found staged control charts to be an effective tool to quantify and demonstrate the “before and after” state of our process improvement activities. However, have you ever considered using them to demonstrate the effects of changes to compensation/incentive plans for your employees?  Here's an example of how a mid-sized... Continue Reading
The 2014-15 NFL season is only days away, and fans all over the country are planning their fall weekends accordingly. In this post, I'm going to use data analysis to answer some questions related to ticket prices, such as: Which team is the least/most expensive to watch at home?  Which team is the least/most expensive to watch on the road?  If you are thinking of a road trip, which stadiums offer... Continue Reading
Screening experimental designs allow you to study a very large number of factors in a very limited number of runs. The objective is to focus on the few factors that have a real effect and eliminate the effects that are not significant. This is often the initial typical objective of any experimenter when a DOE (design of experiments) is performed. Table of Factorial Designs Consider the table below.... Continue Reading
If you’re already a strong user of Minitab Statistical Software, then you’re probably familiar with how to use bar charts to show means, medians, sums, and other statistics. Bar charts are excellent tools, but traditionally used when you want all of your categorical variables to have different sections on the chart. When you want to plot statistics with groups that flow directly from one category... Continue Reading
by Lion "Ari" Ondiappan Arivazhagan, guest blogger In India, we've seen this story far too many times in recent years: Timmanna Hatti, a six-year old boy, was trapped in a 160-feet borewell for more than 5 days in Sulikeri village of Bagalkot district in Karnataka after falling into the well. Perhaps the most heartbreaking aspect of the situation was the decision of the Bagalkot district... Continue Reading
Do you suffer from PAAA (Post-Analysis Assumption Angst)? You’re not alone. Checking the required assumptions for a statistical  analysis is critical. But if you don’t have a Ph.D. in statistics, it can feel more complicated and confusing than the primary analysis itself. How does the cuckoo egg data, a common sample data set often used to teach analysis of variance, satisfy the following formal... Continue Reading
Previously, we looked at how accurate fantasy football rankings were for quarterbacks and tight ends. We found out that rankings for quarterbacks were quite accurate, with most of the top-ranked quarterbacks in the preseason finishing in the top 5 at the end of the season. Tight end rankings had more variation, with 36% of the top 5 preseason tight ends (over the last 5 years) actually finishing... Continue Reading
I caught the end of Toy Story over the weekend, which is definitely one of my all-time favorite children’s movies. Now—unfortunately or fortunately—I can’t get Randy Newman's theme song,“You’ve Got a Friend in Me,” out of my head! It's also got me thinking about the nature of friendship, and how "best friends forever" are supposed to always be there when you need them. And, not to get too maudlin... Continue Reading
Choosing the right type of subgroup in a control chart is crucial. In a rational subgroup, the variability within a subgroup should encompass common causes, random, short-term variability and represent “normal,” “typical,” natural process variations, whereas differences between subgroups are useful to detect drifts in variability over time (due to “special” or “assignable” causes). Variation within... Continue Reading
Learning to ride a bike is a rite of passage for any kid, so much so that we even use the expression "taking the training wheels off" for all kinds of situations. We say it to mean that we are going to let someone perform an activity on their own after removing some safeguard, even though we know they will likely experience failures before becoming proficient at it. You see, riding a bike requires... Continue Reading
NOTE: This story will reveal how easy it can be to optimize settings using the statistical method called Design of Experiments, but it won't provide easy answers for making your own office coffee any better. After her team’s ultimatum about the wretched office coffee, Jill used the design-of-experiments (DOE) tool in Minitab 17’s Assistant to design and analyze a screening study. Jill now knew... Continue Reading