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Statistics

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

In part 2 of this series, we used graphs and tables to see how individual factors affected rates of patient participation in a cardiac rehabilitation program. This initial look at the data indicated that ease of access to the hospital was a very important contributor to patient participation. Given this revelation, a bus or shuttle service for people who do not have cars might be a good way to... Continue Reading
The last thing you want to do when you purchase a new piece of software is spend an excessive amount of time getting up and running. You’ve probably been ready to the use the software since, well, yesterday. Minitab has always focused on making our software easy to use, but many professional software packages do have a steep learning curve. Whatever package you’re using, here are three things you... Continue Reading

7 Deadly Statistical Sins Even the Experts Make

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What does the eyesight of a homeless person have in common with complications from dental anesthesia?  Or with reducing side-effects from cancer? Or monitoring artificial hip implants? These are all subjects of recently published studies that use statistical analyses in Minitab to improve healthcare outcomes. And they're a good reminder  that when we improve the quality of healthcare for others, we... Continue Reading
Suppose you’ve collected data on cycle time, revenue, the dimension of a manufactured part, or some other metric that’s important to you, and you want to see what other variables may be related to it. Now what? When I graduated from college with my first statistics degree, my diploma was bona fide proof that I'd endured hours and hours of classroom lectures on various statistical topics, including l... Continue Reading
My previous post covered the initial phases of a project to attract and retain more patients in a cardiac rehabilitation program, as described in a 2011 Quality Engineering article. A Pareto chart of the reasons enrolled patients left the program indicated that the hospital could do little to encourage participants to attend a greater number of sessions, so the team focused on increasing initial... Continue Reading
Over the past year I've been able to work with and learn from practitioners and experts who are using data analysis and Six Sigma to improve the quality of healthcare, both in terms of operational efficiency and better patient outcomes. I've been struck by how frequently a very basic analysis can lead to remarkable improvements, but some insights cannot be attained without conducting more... Continue Reading
Do you recall my “putting the cart before the horse” analogy in part 1 of this blog series? The comparison is simple. We all, at times, put the cart before the horse in relatively innocuous ways, such as eating your dessert before you’ve eaten your dinner, or deciding what to wear before you’ve been invited to the party. But performing some tasks in the wrong order, such as running a statistical... Continue Reading
For hundreds of years, people having been improving their situation by pulling themselves up by their bootstraps. Well, now you can improve your statistical knowledge by pulling yourself up by your bootstraps. Minitab Express has 7 different bootstrapping analyses that can help you better understand the sampling distribution of your data.  A sampling distribution describes the likelihood of... Continue Reading
Analysis of variance (ANOVA) can determine whether the means of three or more groups are different. ANOVA uses F-tests to statistically test the equality of means. In this post, I’ll show you how ANOVA and F-tests work using a one-way ANOVA example. But wait a minute...have you ever stopped to wonder why you’d use an analysis of variance to determine whether means are different? I'll also show how... Continue Reading
Among the most underutilized statistical tools in Minitab, and I think in general, are multivariate tools. Minitab offers a number of different multivariate tools, including principal component analysis, factor analysis, clustering, and more. In this post, my goal is to give you a better understanding of the multivariate tool called discriminant analysis, and how it can be used. Discriminant... Continue Reading
by Laerte de Araujo Lima, guest blogger The NBA's 2015-16 season will be one for the history books. Not only was it the last season of Kobe Bryan, who scored 60 points in his final game, but the Golden State Warriors set a new wins record, beating the previous record set by 1995-96 Chicago Bulls. The Warriors seem likely to take this season's NBA title, in large part thanks to the performance of... Continue Reading
Once upon a time, when people wanted to compare the standard deviations of two samples, they had two handy tests available, the F-test and Levene's test. Statistical lore has it that the F-test is so named because it so frequently fails you.1 Although the F-test is suitable for data that are normally distributed, its sensitivity to departures from normality limits when and where it can be used. Leve... Continue Reading
The Pareto chart is a graphic representation of the 80/20 rule, also known as the Pareto principle. If you're a quality improvement specialist, you know that the chart is named after the early 20th century economist Vilfredo Pareto, who discovered that roughly 20% of the population in Italy owned about 80% of the property at that time. You probably also know that the Pareto principle was... Continue Reading
In statistics, t-tests are a type of hypothesis test that allows you to compare means. They are called t-tests because each t-test boils your sample data down to one number, the t-value. If you understand how t-tests calculate t-values, you’re well on your way to understanding how these tests work. In this series of posts, I'm focusing on concepts rather than equations to show how t-tests work.... Continue Reading
In the first part of this series, we looked at a case study where staff at a hospital used ATP swab tests to test 8 surfaces for bacteria in 10 different hospital rooms across 5 departments. ATP measurements below 400 units pass the swab test, while measurements greater than or equal to 400 units fail the swab test and require further investigation. I offered two tips on exploring and visualizing... Continue Reading
Working with healthcare-related data often feels different than working with manufacturing data. After all, the common thread among healthcare quality improvement professionals is the motivation to preserve and improve the lives of patients. Whether collecting data on the number of patient falls, patient length-of-stay, bed unavailability, wait times, hospital acquired-infections, or readmissions,... Continue Reading
We often receive questions about moving ranges because they're used in various tools in our statistical software, including control charts and capability analysis when data is not collected in subgroups. In this post, I'll explain what a moving range is, and how a moving range and average moving range are calculated. A moving range measures how variation changes over time when data are collected as... Continue Reading
Along with the explosion of interest in visualizing data over the past few years has been an excessive focus on how attractive the graph is at the expense of how useful it is. Don't get me wrong...I believe that a colorful, modern graph comes across better than a black-and-white, pixelated one. Unfortunately, however, all the talk seems to be about the attractiveness and not the value of the... Continue Reading
As a recent graduate from Arizona State University with a degree in Business Statistics, I had the opportunity to work with students from different areas of study and help analyze data from various projects for them. One particular group asked for help analyzing online survey data they had gathered from other students, and they wanted to see if their new student program was beneficial. I would... Continue Reading
Getting your data from Excel into Minitab Statistical Software for analysis is easy, especially if you keep the following tips in mind. Copy and Paste To paste into Minitab, you can either right-click in the worksheet and choose Paste Cells or you can use Control-V. Minitab allows for 1 row of column headers, so if you have a single row of column info (or no column header info), then you can quickly... Continue Reading