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ANOVA

Blog posts and articles with tips for doing ANOVA (Analysis of Variance), especially for quality improvement initiatives.

In technical support, we often receive questions about Gage R&R and how Minitab calculates the amount of variation that is attributable to the various sources in a measurement system. This post will focus on how the variance components are calculated for a crossed Gage R&R using the ANOVA table, and how we can obtain the %Contribution, StdDev, Study Var and %Study Var shown in the Gage R&R output. ... Continue Reading
It’s safe to say that most people who use statistics are more familiar with parametric analyses than nonparametric analyses. Nonparametric tests are also called distribution-free tests because they don’t assume that your data follow a specific distribution. You may have heard that you should use nonparametric tests when your data don’t meet the assumptions of the parametric test, especially the... Continue Reading
In my recent meetings with people from various companies in the service industries, I realized that one of the problems they face is that they were collecting large amounts of "qualitative" data: types of product, customer profiles, different subsidiaries, several customer requirements, etc. As I discussed in my previous post, one way to look at qualitative data is to use different types of... Continue Reading
Last fall I had a birthday. It wasn’t one of those tougher birthdays where the number ends in a zero. Still, the birthday got me thinking. In response, I told myself, age is just a number. Then I did a mental double-take. Can a statistician say that? After all, numbers are how I understand the world and the way it works. Can age just be a number? After some musing, I concluded that age is just a... Continue Reading
Analysis of variance (ANOVA) is great when you want to compare the differences between group means. For example, you can use ANOVA to assess how three different alloys are related to the mean strength of a product. However, most ANOVA tests assess one response variable at a time, which can be a big problem in certain situations. Fortunately, Minitab statistical software offers a... Continue Reading
We like to host webinars, and our customers and prospects like to attend them. But when our webinar vendor moved from a pay-per-person pricing model to a pay-per-webinar pricing model, we wanted to find out how to maximize registrations and thereby minimize our costs. We collected webinar data on the following variables: Webinar topic Day of week Time of day – 11 a.m. or 2 p.m. Newsletter promotion –... 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
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
by Iván Alfonso, guest blogger I'm a huge fan of hot cakes—they are my favorite dessert ever. I’ve been cooking them for over 15 years, and over that time I’ve noticed many variation in textures, flavor, and thickness. Personally, I like fluffy pancakes. There are many brands of hotcake mix on the market, all with very similar formulations. So I decided to investigate which ingredients and inputs... Continue Reading
If you teach statistics or quality statistics, you’re probably already familiar with the cuckoo egg data set. The common cuckoo has decided that raising baby chicks is a stressful, thankless job. It has better things to do than fill the screeching, gaping maws of cuckoo chicks, day in and day out. So the mother cuckoo lays her eggs in the nests of other bird species. If the cuckoo egg is similar... Continue Reading
After upgrading to the latest and greatest version of our statistical software, Minitab 17, some users have contacted tech support to ask "Wait a minute, where is that Two-Way ANOVA option in Minitab 17?"  The answer is that it’s not there. That’s right! The 2-Way ANOVA option that was available in Minitab 16 and prior versions was removed from Minitab 17.Why would this feature be removed from the... Continue Reading
We received the following question via social media recently: I am using Minitab 17 for ANOVA. I calculated the mean and standard deviation for these 15 values, but the standard deviation is very high. If I delete some values, I can reduce the standard deviation. Is there an option in Minitab that will automatically indicate values that are out of range and delete them so that the standard... Continue Reading
There is more than just the p value in a probability plot—the overall graphical pattern also provides a great deal of useful information. Probability plots are a powerful tool to better understand your data. In this post, I intend to present the main principles of probability plots and focus on their visual interpretation using some real data. In probability plots, the data density distribution... Continue Reading
When you're evaluating a dataset, graphical analysis can be very important. While an analysis like a regression or ANOVA can be backed up by numbers, being able to visualize how your dataset is behaving can be even more convincing than a group of p-values—especially to those who aren’t trained in statistics. For example, let’s look at a few variables we think may be correlated. In this specific... Continue Reading
One-way ANOVA can detect differences between the means of three or more groups. It’s such a classic statistical analysis that it’s hard to imagine it changing much. However, a revolution has been under way for a while now. Fisher's classic one-way ANOVA, which is taught in Stats 101 courses everywhere, may well be obsolete thanks to Welch’s ANOVA. In this post, I not only want to introduce you to... Continue Reading
by Laerte de Araujo Lima, guest blogger In a previous post (How Data Analysis Can Help Us Predict This Year's Champions League), I shared how I used Minitab Statistical Softwareto predict the 2013-2014 season of the UEFA Champions league. This involved the regression analysis of main critical-to-quality (CTQ) factors, which I identified using the “voice of the customer” suggestions of some... Continue Reading
Transformations and non-normal distributions are typically the first approaches considered when the when the Normality test fails in a capability analysis. These approaches do not work when there are extreme outliers because they both assume the data come from a single common-cause variation distribution. But because extreme outliers typically represent special-cause variation, transformations... Continue Reading
Why should you care about Minitab 17 Statistical Software, the newest version of the leading software used for quality improvement and statistics education?   Because important people in your life -- your co-workers, your students, your kids, your boss, maybe even you -- are afraid to analyze data.   There's no shame in that. In fact, there are pretty good reasons for people to feel some trepidation... Continue Reading
Face it, you love regression analysis as much as I do. Regression is one of the most satisfying analyses in Minitab: get some predictors that should have a relationship to a response, go through a model selection process, interpret fit statistics like adjusted R2 and predicted R2, and make predictions. Yes, regression really is quite wonderful. Except when it’s not. Dark, seedy corners of the data... Continue Reading