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How to Interpret a Regression Model with Low R-squared and Low P values

In regression analysis, you'd like your regression model to have significant variables and to produce a high R-squared value. This low P value / high R2 combination indicates that changes in the predictors are related to changes in the response variable and that your model explains a lot of the response variability.

This combination seems to go together naturally. But what if your regression model has significant variables but explains little of the variability? It has low P values and a low R-squared.

At first glance, this combination doesn’t make sense. Are the significant predictors still...

The 6 coolest tools on Minitab's toolbars

Toolbars are there to make your life easier, but if you don’t take the time to hover over each button and wait for a description, it’s pretty easy to never know that there’s a faster way to do something.

The toolbars in Minitab Statistical Software include some pretty nifty shortcuts. Here are my favorite 6:

StatGuide

As soon as you have results in Minitab, the StatGuide button becomes active on your toolbar. Click the button, and the StatGuide opens directly to guidance for the analysis that you’re looking at. Minitab saves you the time you would have spent looking for information about your...

Why Is this Yorkie So Irritated? Oversimplified Statistical Models

You know what really gets on my nerves? A lot of things.

That slow, slinky way that cats walk by. Grrrr.

The rude, abrupt arrival of delivery persons in their obnoxiously loud trucks. (Why do they always pull up just as I’m settling down for a nap?) Grrrr.

Total strangers who reach down and poke me with fat, clumsy fingers that reek of antibacterial soap. Grrrr.

And this one always gets my dander up: Me and the human are out on a walk when some passerby  stops and points at me.

“What a cutie. How old is she?”

"What insolence!" I'll yap back. "I’m a he! And how old are YOU!!?"

Then I’m told to shut up.

“...

Do the Data Really Say Female-Named Hurricanes Are More Deadly?

A recent study has indicated that female-named hurricanes kill more people than male hurricanes. Of course, the title of that article (and other articles like it) is a bit misleading. The study found a significant interaction between the damage caused by the storm and the perceived masculinity or femininity of the hurricane names. So don’t be confused by stories that suggest all female-named hurricanes are deadlier than male-named hurricanes. The study actually found no effect of masculinity/femininity for less severe storms. It was the more severe storms where the gender of the name had a...

I Think I Can, I Know I Can: A High-Level Overview of Process Capability Analysis

Remember "The Little Engine That Could," the children's story about self-confidence in the face of huge challenges? In it, a train engine keeps telling itself "I think I can" while carrying a very heavy load up a big mountain. Next thing you know, the little engine has done it...but until that moment, the outcome was uncertain.

It's a wonderful story for teaching kids about self-confidence. But from a quality and customer service viewpoint, it's a horror story: if your business depends on taking the load up the hill, you want to know you can do it.

That's where capability analysis comes in. 

When...

Hypothesis Testing and P Values

by Matthew Barsalou, guest blogger

Programs such as the Minitab Statistical Software make hypothesis testing easier; but no program can think for the experimenter. Anybody performing a statistical hypothesis test must understand what p values mean in regards to their statistical results as well as potential limitations of statistical hypothesis testing.

A p value of 0.05 is frequently used during statistical hypothesis testing. This p value indicates that if there is no effect (or if the null hypothesis is true), you’d obtain the observed difference or more in 5% of studies due to random...

The 2-3-2 format vs. the 2-2-1-1-1 in the NBA Finals

From 1985 until 2013, the NBA Finals used a 2-3-2 format to decide the NBA Champion. That is, the first 2 games are played at one team’s arena, followed by 3 in a row at the other team’s, then the last two at the first team’s. However, this year they are changing to the 2-2-1-1-1 format, where each team plays 2 of the first four games at home, then they alternate each game for games 5-7.

So how does this change affect the series? Obviously, it doesn’t change the probability of either team winning or losing. At the end of the day there are still 4 games at one team’s home arena, and 3 at...

Multiple Regression Analysis and Response Optimization Examples using the Assistant in Minitab 17

In Minitab, the Assistant menu is your interactive guide to choosing the right tool, analyzing data correctly, and interpreting the results. If you’re feeling a bit rusty with choosing and using a particular analysis, the Assistant is your friend!

Previously, I’ve written about the new linear model features in Minitab 17. In this post, I’ll work through a multiple regression analysis example and optimize the response variable to highlight the new features in the Assistant.

Choose a Regression Analysis

As part of a solar energy test, researchers measured the total heat flux. They found that heat...

The Five Coolest Things You Can Do When You Right-click a Graph in Minitab Statistical Software

Minitab graphs are powerful tools for investigating your process further and removing any doubt about the steps you should take to improve it. With that in mind, you’ll want to know every feature about Minitab graphs that can help you share and communicate your results effectively. While many ways to modify your graph are on the Editor menu, some of the best features become available when you right-click your graph.

Here are the five coolest things you can do when you right-click a graph in Minitab Statistical Software.

Send graph to...

Once your graph is ready for your report or presentation,...

"Hidden Helpers" in Minitab Statistical Software

Minitab Statistical Software offers many features that can save you time and effort when you’re learning statistics or analyzing data. However, when we demonstrate many of these short cuts, tools, and capabilities at shows and events, we find that even some longtime users aren’t aware of them.

I asked members of our sales team and technical support staff to list some of Minitab’s most helpful, yet frequently overlooked features. How many do you use—or want to start using?

Can You Repeat That?

Frequently, you’ll need to modify or re-run some part of an analysis you conducted. You can easily return...

Common Statistical Mistakes You Should Avoid

It's all too easy to make mistakes involving statistics. Powerful statistical software can remove a lot of the difficulty surrounding statistical calculation, reducing the risk of mathematical errors—but  correctly interpreting the results of an analysis can be even more challenging. 

No one knows that better than Minitab's technical trainers. All of our trainers are seasoned statisticians with years of quality improvement experience. They spend most of the year traveling around the country (and around the world) to help people learn to make the best use of Minitab software for analyzing data...

An Unlikely Statistician: Florence Nightingale

Many of my close friends and family members are nurses, and I’ve noticed (via Facebook of course) that many recently celebrated National Nurses’ Week, which ran Tuesday, May 6 through Monday, May 12—the actual birthday of Florence Nightingale.

Florence Nightingale is known as the founder of modern nursing, but you might not know that she is also a celebrated statistician. When I started reading more about her contributions to statistics, I was surprised to find that she used statistics to not only learn more about how many people died during wartime, and why, but also as a way to visually...

Gage This or Gage That? How the Number of Distinct Categories Relates to the %Study Variation

We cannot improve what we cannot measure. Therefore, it is critical that we conduct a measurement systems analysis (MSA) before we start analyzing our data to make any kind of decisions.

When conducting an MSA for continuous measurements, we typically using a Gage R&R Study. And in these Gage R&R Studies, we look at output such as the percentage study variation (%Study Var, or %SV) and the Number of Distinct Categories (ndc) to assess whether our measurement system is adequate.

Looking at these 2 values to assess a measurement system often leads to questions like "Should I look at both values? ...

Using Predict in Minitab 17 to Validate a Statistical Model

Last time I posted, I showed you how to divide a data set into training and validation samples in Minitab with the promise that next time I would show you a way to use the validation sample. Regression is a good analysis for this, because a validation data set can help you to verify that you’ve selected the best model. I’m going to use a hypothetical example so that you can see how it works when we really know the correct model to use. This will let me show you how Minitab 17’s Predict makes it easy to get the numbers that you need to evaluate your model with the training data set.

(The steps...

Five Guidelines for Using P values

There is high pressure to find low P values. Obtaining a low P value for a hypothesis test is make or break because it can lead to funding, articles, and prestige. Statistical significance is everything!

My two previous posts looked at several issues related to P values:

In this post, I’ll look at whether P values are still helpful and provide guidelines on how to use them with these issues in mind.

Sir Ronald A Fisher

Are P Values Still Valuable?

Given...

Exponential: How a Poor Memory Helps to Model Failure Data

These days, my memory isn't what it used to be. Besides that, my memory isn't what it used to be. 

But my incurable case of CRS (Can't Remember Stuff) is not nearly as bad as that of the exponential distribution.

When modelling failure data for reliability analysis, the exponential distribution is completely memoryless. It retains no record of the previous failure of an item.

That might sound like a bad thing. But this special characteristic makes the distribution extremely useful for modelling the behavior of items that have a constant failure rate.

Using the Exponential Distribution to Model...

When Will I Ever See This Statistics Software Again?

Minitab Statistical Software was born out of a desire to make statistics easier to learn: by making the calculations faster and easier with computers, the trio of educators who created the first version of Minitab sought to free students from intensive computations to focus on learning key statistical concepts. That approach resonated with statistics instructors, and today Minitab is the standard for teaching and learning statistics at more than 4,000 universities all over the world.

But many students seem to believe Minitab is used only in education. Search Twitter for "Minitab," and you're...

Proving My Toddler Really Doesn’t Know her Left Foot from her Right

"Do it myself!

If only I had a nickel for every time I heard that phrase from my toddler in a given day. From throwing away trash, to putting frozen waffles in the toaster, to feeding the dog, I hear it so often that I could possibly retire with all the nickels I’d collect.

And of course, I hear this proclamation every single time my 2-year-old puts on her shoes.

What happens when a toddler tries to put on their own shoes? Well, at least in the case of my little one, the left shoe goes on the right foot, and the right shoe on the left foot, followed by a triumphant “Do it myself! Yay!!!” And the...

Chaos at the Kentucky Derby? Bet on It!

If betting wasn't allowed on horse racing, the Kentucky Derby would likely be a little-known event of interest only to a small group of horse racing enthusiasts. But like the Tour de France, the World Cup, and the Masters Tournament, even those with little or no knowledge of the sport in general seem drawn to the excitement over its premier event—the mint juleps, the hats...and of course, the betting.

As most of you probably already know, then, a big part of betting is the odds placed on a particular horse, so that a bet on the favorite to win the race would pay out significantly less than a...

Not All P Values are Created Equal

The interpretation of P values would seem to be fairly standard between different studies. Even if two hypothesis tests study different subject matter, we tend to assume that you can interpret a P value of 0.03 the same way for both tests. A P value is a P value, right?

Not so fast! While Minitab statistical software can correctly calculate all P values, it can’t factor in the larger context of the study. You and your common sense need to do that!

In this post, I’ll demonstrate that P values tell us very different things depending on the larger context.

Recap: P Values Are Not the Probability of...