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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.

In 1898, Russian economist Ladislaus Bortkiewicz published his first statistics book entitled Das Gesetz der keinem Zahlen, in which he included an example that eventually became famous for illustrating the Poisson distribution. Bortkiewicz researched the annual deaths by horse kicks in the Prussian Army from 1875-1984. Data was recorded from 14 different army corps, with one being the Guard... Continue Reading
The Cp and Cpk are well known capability indices commonly used to ensure that a process spread is as small as possible compared to the tolerance interval (Cp), or that it stays well within specifications (Cpk). Yet another type of capability index exists: the Cpm, which is much less known and used less frequently. The main difference between the Cpm and the other capability indices is that the... Continue Reading
The two previous posts in this series focused on manipulating data using Minitab’s calculator and the Data menu. In this third and final post, we continue to explore helpful features for working with text data and will focus on some new features in Minitab 17.2’s Editor menu. Using the Editor Menu  The Editor menu is unique in that the options displayed depend on what is currently active... Continue Reading
My previous post focused on manipulating text data using Minitab’s calculator. In this post we continue to explore some of the useful tools for working with text data, and here we’ll focus on Minitab 17.2’s Data menu. This is the second in a 3-part series, and in the final post we’ll look at the new features in Minitab 17.2’s Editor menu. Using the Data Menu When I think of the Data menu, I think... Continue Reading
With Minitab, it’s easy to create graphs and manage numeric, date/time and text data.  Now Minitab 17.2’s enhanced data manipulation features make it even easier to work with text data. This is the first of three posts in which I'm going to focus on various tools in Minitab that are useful when working with text data, including the Calculator, the Data menu, and the Editor menu. Using the Calculator Y... Continue Reading
As a member of Minitab's Technical Support team, I get the opportunity to work with many people using DOE (Design of Experiments). People often will call after they've already chosen their design, run the experiment, and identified the important factors in their process. But now what? They have to find the best settings, but with several factors and responses, what should they do? "I wish I had a... Continue Reading
In this series of posts, I show how hypothesis tests and confidence intervals work by focusing on concepts and graphs rather than equations and numbers.   Previously, I used graphs to show what statistical significance really means. In this post, I’ll explain both confidence intervals and confidence levels, and how they’re closely related to P values and significance levels. How to Correctly... Continue Reading
Minitab 17.2 is available. You can check out all of the new stuff on the What’s New Page, but I would say that a little demonstration is in order. Here are some new shortcuts that make arranging your data easier in Minitab 17.2. Sorting Let’s suppose that you had copied some Human Development Index data into Minitab and wanted to sort countries in the order of their rank. In the past, you would have... Continue Reading
To choose the right statistical analysis, you need to know the distribution of your data. Suppose you want to assess the capability of your process. If you conduct an analysis that assumes the data follow a normal distribution when, in fact, the data are nonnormal, your results will be inaccurate. To avoid this costly error, you must determine the distribution of your data. So, how do you determine... Continue Reading
Imagine that you are watching a race and that you are located close to the finish line. When the first and fastest runners complete the race, the differences in times between them will probably be quite small. Now wait until the last runners arrive and consider their finishing times. For these slowest runners, the differences in completion times will be extremely large. This is due to the fact that... Continue Reading
by Lion "Ari" Ondiappan Arivazhagan, guest blogger.   Predicting project completion times is one of the major challenges project managers face. Project schedule overruns are quite common due to the high uncertainty in estimating the amount of time activities require, a lack of historical data about project completion, organizational culture, inadequate skills, the complex and elaborative nature of... Continue Reading
This is a companion post for a series of blog posts about understanding hypothesis tests. In this series, I create a graphical equivalent to a 1-sample t-test and confidence interval to help you understand how it works more intuitively. This post focuses entirely on the steps required to create the graphs. It’s a fairly technical and task-oriented post designed for those who need to create the... Continue Reading
I always knew I was different. Even as a kid. “Is that me? Way out there in left field?” I asked the doc. “Yes,” he nodded, as he looked at my chart. “I used brushing to identify you on the graph.” I wasn’t sure I liked getting brushed. It felt like my true identify was being detected and displayed in a window for all to see. The doctor must have sensed my discomfort. “It’s not uncommon—even for those... Continue Reading
Monte Carlo simulation has all kinds of useful manufacturing applications. And - in celebration of Pi Day - I thought it would be apropos to show how you can even use Monte Carlo simulation to estimate pi, which of course is the mathematical constant that represents the ratio of a circle’s circumference to its diameter. For our example, let’s start with a circle of radius 1 inscribed within a... Continue Reading
What do significance levels and P values mean in hypothesis tests? What is statistical significance anyway? In this post, I’ll continue to focus on concepts and graphs to help you gain a more intuitive understanding of how hypothesis tests work in statistics. To bring it to life, I’ll add the significance level and P value to the graph in my previous post in order to perform a graphical version of... Continue Reading
We’ve been pretty excited about March Madness here at Minitab. Kevin Rudy’s been busy creating his regression model and predicting the winners for the 2015 NCAA Men’s Basketball Tournament. But we’re not the only ones. Lots of folks are doing their best analysis to help you plan out your bracket now that the tip-offs for the round of 64 are just a day away. As you ponder your last-minute changes,... Continue Reading
Our vacation planning has begun. My daughter has requested a trip to Disney World as her high school graduation present. For most people, trip planning might mean a simple phone call to the local travel agent or an even simpler do-it-yourself online booking. Not for me. As a statistician, a request like this means I’ve got a lot of data analysis ahead. So many travel questions require (in my... Continue Reading
Are you ready for some madness? Me too! So let’s break down the brackets. I’ll be using the Sagarin Predictor ratings to determine the probability each team has of advancing using a binary logistic model created with Minitab Statistical Software. You can find the details of how the probabilities are being calculated here. Before we start, I’d also like to mention one other set of basketball... Continue Reading
The NCAA Tournament is right around the corner, and you know what that means: It’s time to start thinking about how you’re going to fill out your bracket! For the last two years I’ve used the Sagarin Predictor Ratings to predict the tournament. However, there is a problem with that strategy this year. The old method uses a regression model that calculates the probability one team has of beating... Continue Reading
Welcome to the Hypothesis Test Casino! The featured game of the house is roulette. But this is no ordinary game of roulette. This is p-value roulette! Here’s how it works: We have two roulette wheels, the Null wheel and the Alternative wheel. Each wheel has 20 slots (instead of the usual 37 or 38). You get to bet on one slot. What happens if the ball lands in the slot you bet on? Well, that depends... Continue Reading